Root/fs/exec.c

1/*
2 * linux/fs/exec.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
7/*
8 * #!-checking implemented by tytso.
9 */
10/*
11 * Demand-loading implemented 01.12.91 - no need to read anything but
12 * the header into memory. The inode of the executable is put into
13 * "current->executable", and page faults do the actual loading. Clean.
14 *
15 * Once more I can proudly say that linux stood up to being changed: it
16 * was less than 2 hours work to get demand-loading completely implemented.
17 *
18 * Demand loading changed July 1993 by Eric Youngdale. Use mmap instead,
19 * current->executable is only used by the procfs. This allows a dispatch
20 * table to check for several different types of binary formats. We keep
21 * trying until we recognize the file or we run out of supported binary
22 * formats.
23 */
24
25#include <linux/slab.h>
26#include <linux/file.h>
27#include <linux/fdtable.h>
28#include <linux/mm.h>
29#include <linux/stat.h>
30#include <linux/fcntl.h>
31#include <linux/smp_lock.h>
32#include <linux/swap.h>
33#include <linux/string.h>
34#include <linux/init.h>
35#include <linux/pagemap.h>
36#include <linux/perf_counter.h>
37#include <linux/highmem.h>
38#include <linux/spinlock.h>
39#include <linux/key.h>
40#include <linux/personality.h>
41#include <linux/binfmts.h>
42#include <linux/utsname.h>
43#include <linux/pid_namespace.h>
44#include <linux/module.h>
45#include <linux/namei.h>
46#include <linux/proc_fs.h>
47#include <linux/mount.h>
48#include <linux/security.h>
49#include <linux/ima.h>
50#include <linux/syscalls.h>
51#include <linux/tsacct_kern.h>
52#include <linux/cn_proc.h>
53#include <linux/audit.h>
54#include <linux/tracehook.h>
55#include <linux/kmod.h>
56#include <linux/fsnotify.h>
57#include <linux/fs_struct.h>
58
59#include <asm/uaccess.h>
60#include <asm/mmu_context.h>
61#include <asm/tlb.h>
62#include "internal.h"
63
64int core_uses_pid;
65char core_pattern[CORENAME_MAX_SIZE] = "core";
66int suid_dumpable = 0;
67
68/* The maximal length of core_pattern is also specified in sysctl.c */
69
70static LIST_HEAD(formats);
71static DEFINE_RWLOCK(binfmt_lock);
72
73int __register_binfmt(struct linux_binfmt * fmt, int insert)
74{
75    if (!fmt)
76        return -EINVAL;
77    write_lock(&binfmt_lock);
78    insert ? list_add(&fmt->lh, &formats) :
79         list_add_tail(&fmt->lh, &formats);
80    write_unlock(&binfmt_lock);
81    return 0;
82}
83
84EXPORT_SYMBOL(__register_binfmt);
85
86void unregister_binfmt(struct linux_binfmt * fmt)
87{
88    write_lock(&binfmt_lock);
89    list_del(&fmt->lh);
90    write_unlock(&binfmt_lock);
91}
92
93EXPORT_SYMBOL(unregister_binfmt);
94
95static inline void put_binfmt(struct linux_binfmt * fmt)
96{
97    module_put(fmt->module);
98}
99
100/*
101 * Note that a shared library must be both readable and executable due to
102 * security reasons.
103 *
104 * Also note that we take the address to load from from the file itself.
105 */
106SYSCALL_DEFINE1(uselib, const char __user *, library)
107{
108    struct file *file;
109    char *tmp = getname(library);
110    int error = PTR_ERR(tmp);
111
112    if (IS_ERR(tmp))
113        goto out;
114
115    file = do_filp_open(AT_FDCWD, tmp,
116                O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
117                MAY_READ | MAY_EXEC | MAY_OPEN);
118    putname(tmp);
119    error = PTR_ERR(file);
120    if (IS_ERR(file))
121        goto out;
122
123    error = -EINVAL;
124    if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
125        goto exit;
126
127    error = -EACCES;
128    if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
129        goto exit;
130
131    fsnotify_open(file->f_path.dentry);
132
133    error = -ENOEXEC;
134    if(file->f_op) {
135        struct linux_binfmt * fmt;
136
137        read_lock(&binfmt_lock);
138        list_for_each_entry(fmt, &formats, lh) {
139            if (!fmt->load_shlib)
140                continue;
141            if (!try_module_get(fmt->module))
142                continue;
143            read_unlock(&binfmt_lock);
144            error = fmt->load_shlib(file);
145            read_lock(&binfmt_lock);
146            put_binfmt(fmt);
147            if (error != -ENOEXEC)
148                break;
149        }
150        read_unlock(&binfmt_lock);
151    }
152exit:
153    fput(file);
154out:
155      return error;
156}
157
158#ifdef CONFIG_MMU
159
160static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
161        int write)
162{
163    struct page *page;
164    int ret;
165
166#ifdef CONFIG_STACK_GROWSUP
167    if (write) {
168        ret = expand_stack_downwards(bprm->vma, pos);
169        if (ret < 0)
170            return NULL;
171    }
172#endif
173    ret = get_user_pages(current, bprm->mm, pos,
174            1, write, 1, &page, NULL);
175    if (ret <= 0)
176        return NULL;
177
178    if (write) {
179        unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
180        struct rlimit *rlim;
181
182        /*
183         * We've historically supported up to 32 pages (ARG_MAX)
184         * of argument strings even with small stacks
185         */
186        if (size <= ARG_MAX)
187            return page;
188
189        /*
190         * Limit to 1/4-th the stack size for the argv+env strings.
191         * This ensures that:
192         * - the remaining binfmt code will not run out of stack space,
193         * - the program will have a reasonable amount of stack left
194         * to work from.
195         */
196        rlim = current->signal->rlim;
197        if (size > rlim[RLIMIT_STACK].rlim_cur / 4) {
198            put_page(page);
199            return NULL;
200        }
201    }
202
203    return page;
204}
205
206static void put_arg_page(struct page *page)
207{
208    put_page(page);
209}
210
211static void free_arg_page(struct linux_binprm *bprm, int i)
212{
213}
214
215static void free_arg_pages(struct linux_binprm *bprm)
216{
217}
218
219static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
220        struct page *page)
221{
222    flush_cache_page(bprm->vma, pos, page_to_pfn(page));
223}
224
225static int __bprm_mm_init(struct linux_binprm *bprm)
226{
227    int err;
228    struct vm_area_struct *vma = NULL;
229    struct mm_struct *mm = bprm->mm;
230
231    bprm->vma = vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
232    if (!vma)
233        return -ENOMEM;
234
235    down_write(&mm->mmap_sem);
236    vma->vm_mm = mm;
237
238    /*
239     * Place the stack at the largest stack address the architecture
240     * supports. Later, we'll move this to an appropriate place. We don't
241     * use STACK_TOP because that can depend on attributes which aren't
242     * configured yet.
243     */
244    vma->vm_end = STACK_TOP_MAX;
245    vma->vm_start = vma->vm_end - PAGE_SIZE;
246    vma->vm_flags = VM_STACK_FLAGS;
247    vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
248    err = insert_vm_struct(mm, vma);
249    if (err)
250        goto err;
251
252    mm->stack_vm = mm->total_vm = 1;
253    up_write(&mm->mmap_sem);
254    bprm->p = vma->vm_end - sizeof(void *);
255    return 0;
256err:
257    up_write(&mm->mmap_sem);
258    bprm->vma = NULL;
259    kmem_cache_free(vm_area_cachep, vma);
260    return err;
261}
262
263static bool valid_arg_len(struct linux_binprm *bprm, long len)
264{
265    return len <= MAX_ARG_STRLEN;
266}
267
268#else
269
270static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
271        int write)
272{
273    struct page *page;
274
275    page = bprm->page[pos / PAGE_SIZE];
276    if (!page && write) {
277        page = alloc_page(GFP_HIGHUSER|__GFP_ZERO);
278        if (!page)
279            return NULL;
280        bprm->page[pos / PAGE_SIZE] = page;
281    }
282
283    return page;
284}
285
286static void put_arg_page(struct page *page)
287{
288}
289
290static void free_arg_page(struct linux_binprm *bprm, int i)
291{
292    if (bprm->page[i]) {
293        __free_page(bprm->page[i]);
294        bprm->page[i] = NULL;
295    }
296}
297
298static void free_arg_pages(struct linux_binprm *bprm)
299{
300    int i;
301
302    for (i = 0; i < MAX_ARG_PAGES; i++)
303        free_arg_page(bprm, i);
304}
305
306static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
307        struct page *page)
308{
309}
310
311static int __bprm_mm_init(struct linux_binprm *bprm)
312{
313    bprm->p = PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *);
314    return 0;
315}
316
317static bool valid_arg_len(struct linux_binprm *bprm, long len)
318{
319    return len <= bprm->p;
320}
321
322#endif /* CONFIG_MMU */
323
324/*
325 * Create a new mm_struct and populate it with a temporary stack
326 * vm_area_struct. We don't have enough context at this point to set the stack
327 * flags, permissions, and offset, so we use temporary values. We'll update
328 * them later in setup_arg_pages().
329 */
330int bprm_mm_init(struct linux_binprm *bprm)
331{
332    int err;
333    struct mm_struct *mm = NULL;
334
335    bprm->mm = mm = mm_alloc();
336    err = -ENOMEM;
337    if (!mm)
338        goto err;
339
340    err = init_new_context(current, mm);
341    if (err)
342        goto err;
343
344    err = __bprm_mm_init(bprm);
345    if (err)
346        goto err;
347
348    return 0;
349
350err:
351    if (mm) {
352        bprm->mm = NULL;
353        mmdrop(mm);
354    }
355
356    return err;
357}
358
359/*
360 * count() counts the number of strings in array ARGV.
361 */
362static int count(char __user * __user * argv, int max)
363{
364    int i = 0;
365
366    if (argv != NULL) {
367        for (;;) {
368            char __user * p;
369
370            if (get_user(p, argv))
371                return -EFAULT;
372            if (!p)
373                break;
374            argv++;
375            if (i++ >= max)
376                return -E2BIG;
377            cond_resched();
378        }
379    }
380    return i;
381}
382
383/*
384 * 'copy_strings()' copies argument/environment strings from the old
385 * processes's memory to the new process's stack. The call to get_user_pages()
386 * ensures the destination page is created and not swapped out.
387 */
388static int copy_strings(int argc, char __user * __user * argv,
389            struct linux_binprm *bprm)
390{
391    struct page *kmapped_page = NULL;
392    char *kaddr = NULL;
393    unsigned long kpos = 0;
394    int ret;
395
396    while (argc-- > 0) {
397        char __user *str;
398        int len;
399        unsigned long pos;
400
401        if (get_user(str, argv+argc) ||
402                !(len = strnlen_user(str, MAX_ARG_STRLEN))) {
403            ret = -EFAULT;
404            goto out;
405        }
406
407        if (!valid_arg_len(bprm, len)) {
408            ret = -E2BIG;
409            goto out;
410        }
411
412        /* We're going to work our way backwords. */
413        pos = bprm->p;
414        str += len;
415        bprm->p -= len;
416
417        while (len > 0) {
418            int offset, bytes_to_copy;
419
420            offset = pos % PAGE_SIZE;
421            if (offset == 0)
422                offset = PAGE_SIZE;
423
424            bytes_to_copy = offset;
425            if (bytes_to_copy > len)
426                bytes_to_copy = len;
427
428            offset -= bytes_to_copy;
429            pos -= bytes_to_copy;
430            str -= bytes_to_copy;
431            len -= bytes_to_copy;
432
433            if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
434                struct page *page;
435
436                page = get_arg_page(bprm, pos, 1);
437                if (!page) {
438                    ret = -E2BIG;
439                    goto out;
440                }
441
442                if (kmapped_page) {
443                    flush_kernel_dcache_page(kmapped_page);
444                    kunmap(kmapped_page);
445                    put_arg_page(kmapped_page);
446                }
447                kmapped_page = page;
448                kaddr = kmap(kmapped_page);
449                kpos = pos & PAGE_MASK;
450                flush_arg_page(bprm, kpos, kmapped_page);
451            }
452            if (copy_from_user(kaddr+offset, str, bytes_to_copy)) {
453                ret = -EFAULT;
454                goto out;
455            }
456        }
457    }
458    ret = 0;
459out:
460    if (kmapped_page) {
461        flush_kernel_dcache_page(kmapped_page);
462        kunmap(kmapped_page);
463        put_arg_page(kmapped_page);
464    }
465    return ret;
466}
467
468/*
469 * Like copy_strings, but get argv and its values from kernel memory.
470 */
471int copy_strings_kernel(int argc,char ** argv, struct linux_binprm *bprm)
472{
473    int r;
474    mm_segment_t oldfs = get_fs();
475    set_fs(KERNEL_DS);
476    r = copy_strings(argc, (char __user * __user *)argv, bprm);
477    set_fs(oldfs);
478    return r;
479}
480EXPORT_SYMBOL(copy_strings_kernel);
481
482#ifdef CONFIG_MMU
483
484/*
485 * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX. Once
486 * the binfmt code determines where the new stack should reside, we shift it to
487 * its final location. The process proceeds as follows:
488 *
489 * 1) Use shift to calculate the new vma endpoints.
490 * 2) Extend vma to cover both the old and new ranges. This ensures the
491 * arguments passed to subsequent functions are consistent.
492 * 3) Move vma's page tables to the new range.
493 * 4) Free up any cleared pgd range.
494 * 5) Shrink the vma to cover only the new range.
495 */
496static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
497{
498    struct mm_struct *mm = vma->vm_mm;
499    unsigned long old_start = vma->vm_start;
500    unsigned long old_end = vma->vm_end;
501    unsigned long length = old_end - old_start;
502    unsigned long new_start = old_start - shift;
503    unsigned long new_end = old_end - shift;
504    struct mmu_gather *tlb;
505
506    BUG_ON(new_start > new_end);
507
508    /*
509     * ensure there are no vmas between where we want to go
510     * and where we are
511     */
512    if (vma != find_vma(mm, new_start))
513        return -EFAULT;
514
515    /*
516     * cover the whole range: [new_start, old_end)
517     */
518    vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL);
519
520    /*
521     * move the page tables downwards, on failure we rely on
522     * process cleanup to remove whatever mess we made.
523     */
524    if (length != move_page_tables(vma, old_start,
525                       vma, new_start, length))
526        return -ENOMEM;
527
528    lru_add_drain();
529    tlb = tlb_gather_mmu(mm, 0);
530    if (new_end > old_start) {
531        /*
532         * when the old and new regions overlap clear from new_end.
533         */
534        free_pgd_range(tlb, new_end, old_end, new_end,
535            vma->vm_next ? vma->vm_next->vm_start : 0);
536    } else {
537        /*
538         * otherwise, clean from old_start; this is done to not touch
539         * the address space in [new_end, old_start) some architectures
540         * have constraints on va-space that make this illegal (IA64) -
541         * for the others its just a little faster.
542         */
543        free_pgd_range(tlb, old_start, old_end, new_end,
544            vma->vm_next ? vma->vm_next->vm_start : 0);
545    }
546    tlb_finish_mmu(tlb, new_end, old_end);
547
548    /*
549     * shrink the vma to just the new range.
550     */
551    vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);
552
553    return 0;
554}
555
556#define EXTRA_STACK_VM_PAGES 20 /* random */
557
558/*
559 * Finalizes the stack vm_area_struct. The flags and permissions are updated,
560 * the stack is optionally relocated, and some extra space is added.
561 */
562int setup_arg_pages(struct linux_binprm *bprm,
563            unsigned long stack_top,
564            int executable_stack)
565{
566    unsigned long ret;
567    unsigned long stack_shift;
568    struct mm_struct *mm = current->mm;
569    struct vm_area_struct *vma = bprm->vma;
570    struct vm_area_struct *prev = NULL;
571    unsigned long vm_flags;
572    unsigned long stack_base;
573
574#ifdef CONFIG_STACK_GROWSUP
575    /* Limit stack size to 1GB */
576    stack_base = current->signal->rlim[RLIMIT_STACK].rlim_max;
577    if (stack_base > (1 << 30))
578        stack_base = 1 << 30;
579
580    /* Make sure we didn't let the argument array grow too large. */
581    if (vma->vm_end - vma->vm_start > stack_base)
582        return -ENOMEM;
583
584    stack_base = PAGE_ALIGN(stack_top - stack_base);
585
586    stack_shift = vma->vm_start - stack_base;
587    mm->arg_start = bprm->p - stack_shift;
588    bprm->p = vma->vm_end - stack_shift;
589#else
590    stack_top = arch_align_stack(stack_top);
591    stack_top = PAGE_ALIGN(stack_top);
592    stack_shift = vma->vm_end - stack_top;
593
594    bprm->p -= stack_shift;
595    mm->arg_start = bprm->p;
596#endif
597
598    if (bprm->loader)
599        bprm->loader -= stack_shift;
600    bprm->exec -= stack_shift;
601
602    down_write(&mm->mmap_sem);
603    vm_flags = VM_STACK_FLAGS;
604
605    /*
606     * Adjust stack execute permissions; explicitly enable for
607     * EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X and leave alone
608     * (arch default) otherwise.
609     */
610    if (unlikely(executable_stack == EXSTACK_ENABLE_X))
611        vm_flags |= VM_EXEC;
612    else if (executable_stack == EXSTACK_DISABLE_X)
613        vm_flags &= ~VM_EXEC;
614    vm_flags |= mm->def_flags;
615
616    ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
617            vm_flags);
618    if (ret)
619        goto out_unlock;
620    BUG_ON(prev != vma);
621
622    /* Move stack pages down in memory. */
623    if (stack_shift) {
624        ret = shift_arg_pages(vma, stack_shift);
625        if (ret) {
626            up_write(&mm->mmap_sem);
627            return ret;
628        }
629    }
630
631#ifdef CONFIG_STACK_GROWSUP
632    stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
633#else
634    stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
635#endif
636    ret = expand_stack(vma, stack_base);
637    if (ret)
638        ret = -EFAULT;
639
640out_unlock:
641    up_write(&mm->mmap_sem);
642    return 0;
643}
644EXPORT_SYMBOL(setup_arg_pages);
645
646#endif /* CONFIG_MMU */
647
648struct file *open_exec(const char *name)
649{
650    struct file *file;
651    int err;
652
653    file = do_filp_open(AT_FDCWD, name,
654                O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
655                MAY_EXEC | MAY_OPEN);
656    if (IS_ERR(file))
657        goto out;
658
659    err = -EACCES;
660    if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
661        goto exit;
662
663    if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
664        goto exit;
665
666    fsnotify_open(file->f_path.dentry);
667
668    err = deny_write_access(file);
669    if (err)
670        goto exit;
671
672out:
673    return file;
674
675exit:
676    fput(file);
677    return ERR_PTR(err);
678}
679EXPORT_SYMBOL(open_exec);
680
681int kernel_read(struct file *file, loff_t offset,
682        char *addr, unsigned long count)
683{
684    mm_segment_t old_fs;
685    loff_t pos = offset;
686    int result;
687
688    old_fs = get_fs();
689    set_fs(get_ds());
690    /* The cast to a user pointer is valid due to the set_fs() */
691    result = vfs_read(file, (void __user *)addr, count, &pos);
692    set_fs(old_fs);
693    return result;
694}
695
696EXPORT_SYMBOL(kernel_read);
697
698static int exec_mmap(struct mm_struct *mm)
699{
700    struct task_struct *tsk;
701    struct mm_struct * old_mm, *active_mm;
702
703    /* Notify parent that we're no longer interested in the old VM */
704    tsk = current;
705    old_mm = current->mm;
706    mm_release(tsk, old_mm);
707
708    if (old_mm) {
709        /*
710         * Make sure that if there is a core dump in progress
711         * for the old mm, we get out and die instead of going
712         * through with the exec. We must hold mmap_sem around
713         * checking core_state and changing tsk->mm.
714         */
715        down_read(&old_mm->mmap_sem);
716        if (unlikely(old_mm->core_state)) {
717            up_read(&old_mm->mmap_sem);
718            return -EINTR;
719        }
720    }
721    task_lock(tsk);
722    active_mm = tsk->active_mm;
723    tsk->mm = mm;
724    tsk->active_mm = mm;
725    activate_mm(active_mm, mm);
726    task_unlock(tsk);
727    arch_pick_mmap_layout(mm);
728    if (old_mm) {
729        up_read(&old_mm->mmap_sem);
730        BUG_ON(active_mm != old_mm);
731        mm_update_next_owner(old_mm);
732        mmput(old_mm);
733        return 0;
734    }
735    mmdrop(active_mm);
736    return 0;
737}
738
739/*
740 * This function makes sure the current process has its own signal table,
741 * so that flush_signal_handlers can later reset the handlers without
742 * disturbing other processes. (Other processes might share the signal
743 * table via the CLONE_SIGHAND option to clone().)
744 */
745static int de_thread(struct task_struct *tsk)
746{
747    struct signal_struct *sig = tsk->signal;
748    struct sighand_struct *oldsighand = tsk->sighand;
749    spinlock_t *lock = &oldsighand->siglock;
750    int count;
751
752    if (thread_group_empty(tsk))
753        goto no_thread_group;
754
755    /*
756     * Kill all other threads in the thread group.
757     */
758    spin_lock_irq(lock);
759    if (signal_group_exit(sig)) {
760        /*
761         * Another group action in progress, just
762         * return so that the signal is processed.
763         */
764        spin_unlock_irq(lock);
765        return -EAGAIN;
766    }
767    sig->group_exit_task = tsk;
768    zap_other_threads(tsk);
769
770    /* Account for the thread group leader hanging around: */
771    count = thread_group_leader(tsk) ? 1 : 2;
772    sig->notify_count = count;
773    while (atomic_read(&sig->count) > count) {
774        __set_current_state(TASK_UNINTERRUPTIBLE);
775        spin_unlock_irq(lock);
776        schedule();
777        spin_lock_irq(lock);
778    }
779    spin_unlock_irq(lock);
780
781    /*
782     * At this point all other threads have exited, all we have to
783     * do is to wait for the thread group leader to become inactive,
784     * and to assume its PID:
785     */
786    if (!thread_group_leader(tsk)) {
787        struct task_struct *leader = tsk->group_leader;
788
789        sig->notify_count = -1; /* for exit_notify() */
790        for (;;) {
791            write_lock_irq(&tasklist_lock);
792            if (likely(leader->exit_state))
793                break;
794            __set_current_state(TASK_UNINTERRUPTIBLE);
795            write_unlock_irq(&tasklist_lock);
796            schedule();
797        }
798
799        /*
800         * The only record we have of the real-time age of a
801         * process, regardless of execs it's done, is start_time.
802         * All the past CPU time is accumulated in signal_struct
803         * from sister threads now dead. But in this non-leader
804         * exec, nothing survives from the original leader thread,
805         * whose birth marks the true age of this process now.
806         * When we take on its identity by switching to its PID, we
807         * also take its birthdate (always earlier than our own).
808         */
809        tsk->start_time = leader->start_time;
810
811        BUG_ON(!same_thread_group(leader, tsk));
812        BUG_ON(has_group_leader_pid(tsk));
813        /*
814         * An exec() starts a new thread group with the
815         * TGID of the previous thread group. Rehash the
816         * two threads with a switched PID, and release
817         * the former thread group leader:
818         */
819
820        /* Become a process group leader with the old leader's pid.
821         * The old leader becomes a thread of the this thread group.
822         * Note: The old leader also uses this pid until release_task
823         * is called. Odd but simple and correct.
824         */
825        detach_pid(tsk, PIDTYPE_PID);
826        tsk->pid = leader->pid;
827        attach_pid(tsk, PIDTYPE_PID, task_pid(leader));
828        transfer_pid(leader, tsk, PIDTYPE_PGID);
829        transfer_pid(leader, tsk, PIDTYPE_SID);
830        list_replace_rcu(&leader->tasks, &tsk->tasks);
831
832        tsk->group_leader = tsk;
833        leader->group_leader = tsk;
834
835        tsk->exit_signal = SIGCHLD;
836
837        BUG_ON(leader->exit_state != EXIT_ZOMBIE);
838        leader->exit_state = EXIT_DEAD;
839        write_unlock_irq(&tasklist_lock);
840
841        release_task(leader);
842    }
843
844    sig->group_exit_task = NULL;
845    sig->notify_count = 0;
846
847no_thread_group:
848    exit_itimers(sig);
849    flush_itimer_signals();
850
851    if (atomic_read(&oldsighand->count) != 1) {
852        struct sighand_struct *newsighand;
853        /*
854         * This ->sighand is shared with the CLONE_SIGHAND
855         * but not CLONE_THREAD task, switch to the new one.
856         */
857        newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
858        if (!newsighand)
859            return -ENOMEM;
860
861        atomic_set(&newsighand->count, 1);
862        memcpy(newsighand->action, oldsighand->action,
863               sizeof(newsighand->action));
864
865        write_lock_irq(&tasklist_lock);
866        spin_lock(&oldsighand->siglock);
867        rcu_assign_pointer(tsk->sighand, newsighand);
868        spin_unlock(&oldsighand->siglock);
869        write_unlock_irq(&tasklist_lock);
870
871        __cleanup_sighand(oldsighand);
872    }
873
874    BUG_ON(!thread_group_leader(tsk));
875    return 0;
876}
877
878/*
879 * These functions flushes out all traces of the currently running executable
880 * so that a new one can be started
881 */
882static void flush_old_files(struct files_struct * files)
883{
884    long j = -1;
885    struct fdtable *fdt;
886
887    spin_lock(&files->file_lock);
888    for (;;) {
889        unsigned long set, i;
890
891        j++;
892        i = j * __NFDBITS;
893        fdt = files_fdtable(files);
894        if (i >= fdt->max_fds)
895            break;
896        set = fdt->close_on_exec->fds_bits[j];
897        if (!set)
898            continue;
899        fdt->close_on_exec->fds_bits[j] = 0;
900        spin_unlock(&files->file_lock);
901        for ( ; set ; i++,set >>= 1) {
902            if (set & 1) {
903                sys_close(i);
904            }
905        }
906        spin_lock(&files->file_lock);
907
908    }
909    spin_unlock(&files->file_lock);
910}
911
912char *get_task_comm(char *buf, struct task_struct *tsk)
913{
914    /* buf must be at least sizeof(tsk->comm) in size */
915    task_lock(tsk);
916    strncpy(buf, tsk->comm, sizeof(tsk->comm));
917    task_unlock(tsk);
918    return buf;
919}
920
921void set_task_comm(struct task_struct *tsk, char *buf)
922{
923    task_lock(tsk);
924    strlcpy(tsk->comm, buf, sizeof(tsk->comm));
925    task_unlock(tsk);
926    perf_counter_comm(tsk);
927}
928
929int flush_old_exec(struct linux_binprm * bprm)
930{
931    char * name;
932    int i, ch, retval;
933    char tcomm[sizeof(current->comm)];
934
935    /*
936     * Make sure we have a private signal table and that
937     * we are unassociated from the previous thread group.
938     */
939    retval = de_thread(current);
940    if (retval)
941        goto out;
942
943    set_mm_exe_file(bprm->mm, bprm->file);
944
945    /*
946     * Release all of the old mmap stuff
947     */
948    retval = exec_mmap(bprm->mm);
949    if (retval)
950        goto out;
951
952    bprm->mm = NULL; /* We're using it now */
953
954    /* This is the point of no return */
955    current->sas_ss_sp = current->sas_ss_size = 0;
956
957    if (current_euid() == current_uid() && current_egid() == current_gid())
958        set_dumpable(current->mm, 1);
959    else
960        set_dumpable(current->mm, suid_dumpable);
961
962    name = bprm->filename;
963
964    /* Copies the binary name from after last slash */
965    for (i=0; (ch = *(name++)) != '\0';) {
966        if (ch == '/')
967            i = 0; /* overwrite what we wrote */
968        else
969            if (i < (sizeof(tcomm) - 1))
970                tcomm[i++] = ch;
971    }
972    tcomm[i] = '\0';
973    set_task_comm(current, tcomm);
974
975    current->flags &= ~PF_RANDOMIZE;
976    flush_thread();
977
978    /* Set the new mm task size. We have to do that late because it may
979     * depend on TIF_32BIT which is only updated in flush_thread() on
980     * some architectures like powerpc
981     */
982    current->mm->task_size = TASK_SIZE;
983
984    /* install the new credentials */
985    if (bprm->cred->uid != current_euid() ||
986        bprm->cred->gid != current_egid()) {
987        current->pdeath_signal = 0;
988    } else if (file_permission(bprm->file, MAY_READ) ||
989           bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP) {
990        set_dumpable(current->mm, suid_dumpable);
991    }
992
993    current->personality &= ~bprm->per_clear;
994
995    /*
996     * Flush performance counters when crossing a
997     * security domain:
998     */
999    if (!get_dumpable(current->mm))
1000        perf_counter_exit_task(current);
1001
1002    /* An exec changes our domain. We are no longer part of the thread
1003       group */
1004
1005    current->self_exec_id++;
1006            
1007    flush_signal_handlers(current, 0);
1008    flush_old_files(current->files);
1009
1010    return 0;
1011
1012out:
1013    return retval;
1014}
1015
1016EXPORT_SYMBOL(flush_old_exec);
1017
1018/*
1019 * Prepare credentials and lock ->cred_guard_mutex.
1020 * install_exec_creds() commits the new creds and drops the lock.
1021 * Or, if exec fails before, free_bprm() should release ->cred and
1022 * and unlock.
1023 */
1024int prepare_bprm_creds(struct linux_binprm *bprm)
1025{
1026    if (mutex_lock_interruptible(&current->cred_guard_mutex))
1027        return -ERESTARTNOINTR;
1028
1029    bprm->cred = prepare_exec_creds();
1030    if (likely(bprm->cred))
1031        return 0;
1032
1033    mutex_unlock(&current->cred_guard_mutex);
1034    return -ENOMEM;
1035}
1036
1037void free_bprm(struct linux_binprm *bprm)
1038{
1039    free_arg_pages(bprm);
1040    if (bprm->cred) {
1041        mutex_unlock(&current->cred_guard_mutex);
1042        abort_creds(bprm->cred);
1043    }
1044    kfree(bprm);
1045}
1046
1047/*
1048 * install the new credentials for this executable
1049 */
1050void install_exec_creds(struct linux_binprm *bprm)
1051{
1052    security_bprm_committing_creds(bprm);
1053
1054    commit_creds(bprm->cred);
1055    bprm->cred = NULL;
1056    /*
1057     * cred_guard_mutex must be held at least to this point to prevent
1058     * ptrace_attach() from altering our determination of the task's
1059     * credentials; any time after this it may be unlocked.
1060     */
1061    security_bprm_committed_creds(bprm);
1062    mutex_unlock(&current->cred_guard_mutex);
1063}
1064EXPORT_SYMBOL(install_exec_creds);
1065
1066/*
1067 * determine how safe it is to execute the proposed program
1068 * - the caller must hold current->cred_guard_mutex to protect against
1069 * PTRACE_ATTACH
1070 */
1071int check_unsafe_exec(struct linux_binprm *bprm)
1072{
1073    struct task_struct *p = current, *t;
1074    unsigned n_fs;
1075    int res = 0;
1076
1077    bprm->unsafe = tracehook_unsafe_exec(p);
1078
1079    n_fs = 1;
1080    write_lock(&p->fs->lock);
1081    rcu_read_lock();
1082    for (t = next_thread(p); t != p; t = next_thread(t)) {
1083        if (t->fs == p->fs)
1084            n_fs++;
1085    }
1086    rcu_read_unlock();
1087
1088    if (p->fs->users > n_fs) {
1089        bprm->unsafe |= LSM_UNSAFE_SHARE;
1090    } else {
1091        res = -EAGAIN;
1092        if (!p->fs->in_exec) {
1093            p->fs->in_exec = 1;
1094            res = 1;
1095        }
1096    }
1097    write_unlock(&p->fs->lock);
1098
1099    return res;
1100}
1101
1102/*
1103 * Fill the binprm structure from the inode.
1104 * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
1105 *
1106 * This may be called multiple times for binary chains (scripts for example).
1107 */
1108int prepare_binprm(struct linux_binprm *bprm)
1109{
1110    umode_t mode;
1111    struct inode * inode = bprm->file->f_path.dentry->d_inode;
1112    int retval;
1113
1114    mode = inode->i_mode;
1115    if (bprm->file->f_op == NULL)
1116        return -EACCES;
1117
1118    /* clear any previous set[ug]id data from a previous binary */
1119    bprm->cred->euid = current_euid();
1120    bprm->cred->egid = current_egid();
1121
1122    if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) {
1123        /* Set-uid? */
1124        if (mode & S_ISUID) {
1125            bprm->per_clear |= PER_CLEAR_ON_SETID;
1126            bprm->cred->euid = inode->i_uid;
1127        }
1128
1129        /* Set-gid? */
1130        /*
1131         * If setgid is set but no group execute bit then this
1132         * is a candidate for mandatory locking, not a setgid
1133         * executable.
1134         */
1135        if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
1136            bprm->per_clear |= PER_CLEAR_ON_SETID;
1137            bprm->cred->egid = inode->i_gid;
1138        }
1139    }
1140
1141    /* fill in binprm security blob */
1142    retval = security_bprm_set_creds(bprm);
1143    if (retval)
1144        return retval;
1145    bprm->cred_prepared = 1;
1146
1147    memset(bprm->buf, 0, BINPRM_BUF_SIZE);
1148    return kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
1149}
1150
1151EXPORT_SYMBOL(prepare_binprm);
1152
1153/*
1154 * Arguments are '\0' separated strings found at the location bprm->p
1155 * points to; chop off the first by relocating brpm->p to right after
1156 * the first '\0' encountered.
1157 */
1158int remove_arg_zero(struct linux_binprm *bprm)
1159{
1160    int ret = 0;
1161    unsigned long offset;
1162    char *kaddr;
1163    struct page *page;
1164
1165    if (!bprm->argc)
1166        return 0;
1167
1168    do {
1169        offset = bprm->p & ~PAGE_MASK;
1170        page = get_arg_page(bprm, bprm->p, 0);
1171        if (!page) {
1172            ret = -EFAULT;
1173            goto out;
1174        }
1175        kaddr = kmap_atomic(page, KM_USER0);
1176
1177        for (; offset < PAGE_SIZE && kaddr[offset];
1178                offset++, bprm->p++)
1179            ;
1180
1181        kunmap_atomic(kaddr, KM_USER0);
1182        put_arg_page(page);
1183
1184        if (offset == PAGE_SIZE)
1185            free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
1186    } while (offset == PAGE_SIZE);
1187
1188    bprm->p++;
1189    bprm->argc--;
1190    ret = 0;
1191
1192out:
1193    return ret;
1194}
1195EXPORT_SYMBOL(remove_arg_zero);
1196
1197/*
1198 * cycle the list of binary formats handler, until one recognizes the image
1199 */
1200int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
1201{
1202    unsigned int depth = bprm->recursion_depth;
1203    int try,retval;
1204    struct linux_binfmt *fmt;
1205
1206    retval = security_bprm_check(bprm);
1207    if (retval)
1208        return retval;
1209    retval = ima_bprm_check(bprm);
1210    if (retval)
1211        return retval;
1212
1213    /* kernel module loader fixup */
1214    /* so we don't try to load run modprobe in kernel space. */
1215    set_fs(USER_DS);
1216
1217    retval = audit_bprm(bprm);
1218    if (retval)
1219        return retval;
1220
1221    retval = -ENOENT;
1222    for (try=0; try<2; try++) {
1223        read_lock(&binfmt_lock);
1224        list_for_each_entry(fmt, &formats, lh) {
1225            int (*fn)(struct linux_binprm *, struct pt_regs *) = fmt->load_binary;
1226            if (!fn)
1227                continue;
1228            if (!try_module_get(fmt->module))
1229                continue;
1230            read_unlock(&binfmt_lock);
1231            retval = fn(bprm, regs);
1232            /*
1233             * Restore the depth counter to its starting value
1234             * in this call, so we don't have to rely on every
1235             * load_binary function to restore it on return.
1236             */
1237            bprm->recursion_depth = depth;
1238            if (retval >= 0) {
1239                if (depth == 0)
1240                    tracehook_report_exec(fmt, bprm, regs);
1241                put_binfmt(fmt);
1242                allow_write_access(bprm->file);
1243                if (bprm->file)
1244                    fput(bprm->file);
1245                bprm->file = NULL;
1246                current->did_exec = 1;
1247                proc_exec_connector(current);
1248                return retval;
1249            }
1250            read_lock(&binfmt_lock);
1251            put_binfmt(fmt);
1252            if (retval != -ENOEXEC || bprm->mm == NULL)
1253                break;
1254            if (!bprm->file) {
1255                read_unlock(&binfmt_lock);
1256                return retval;
1257            }
1258        }
1259        read_unlock(&binfmt_lock);
1260        if (retval != -ENOEXEC || bprm->mm == NULL) {
1261            break;
1262#ifdef CONFIG_MODULES
1263        } else {
1264#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
1265            if (printable(bprm->buf[0]) &&
1266                printable(bprm->buf[1]) &&
1267                printable(bprm->buf[2]) &&
1268                printable(bprm->buf[3]))
1269                break; /* -ENOEXEC */
1270            request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
1271#endif
1272        }
1273    }
1274    return retval;
1275}
1276
1277EXPORT_SYMBOL(search_binary_handler);
1278
1279/*
1280 * sys_execve() executes a new program.
1281 */
1282int do_execve(char * filename,
1283    char __user *__user *argv,
1284    char __user *__user *envp,
1285    struct pt_regs * regs)
1286{
1287    struct linux_binprm *bprm;
1288    struct file *file;
1289    struct files_struct *displaced;
1290    bool clear_in_exec;
1291    int retval;
1292
1293    retval = unshare_files(&displaced);
1294    if (retval)
1295        goto out_ret;
1296
1297    retval = -ENOMEM;
1298    bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
1299    if (!bprm)
1300        goto out_files;
1301
1302    retval = prepare_bprm_creds(bprm);
1303    if (retval)
1304        goto out_free;
1305
1306    retval = check_unsafe_exec(bprm);
1307    if (retval < 0)
1308        goto out_free;
1309    clear_in_exec = retval;
1310    current->in_execve = 1;
1311
1312    file = open_exec(filename);
1313    retval = PTR_ERR(file);
1314    if (IS_ERR(file))
1315        goto out_unmark;
1316
1317    sched_exec();
1318
1319    bprm->file = file;
1320    bprm->filename = filename;
1321    bprm->interp = filename;
1322
1323    retval = bprm_mm_init(bprm);
1324    if (retval)
1325        goto out_file;
1326
1327    bprm->argc = count(argv, MAX_ARG_STRINGS);
1328    if ((retval = bprm->argc) < 0)
1329        goto out;
1330
1331    bprm->envc = count(envp, MAX_ARG_STRINGS);
1332    if ((retval = bprm->envc) < 0)
1333        goto out;
1334
1335    retval = prepare_binprm(bprm);
1336    if (retval < 0)
1337        goto out;
1338
1339    retval = copy_strings_kernel(1, &bprm->filename, bprm);
1340    if (retval < 0)
1341        goto out;
1342
1343    bprm->exec = bprm->p;
1344    retval = copy_strings(bprm->envc, envp, bprm);
1345    if (retval < 0)
1346        goto out;
1347
1348    retval = copy_strings(bprm->argc, argv, bprm);
1349    if (retval < 0)
1350        goto out;
1351
1352    current->flags &= ~PF_KTHREAD;
1353    retval = search_binary_handler(bprm,regs);
1354    if (retval < 0)
1355        goto out;
1356
1357    /* execve succeeded */
1358    current->fs->in_exec = 0;
1359    current->in_execve = 0;
1360    acct_update_integrals(current);
1361    free_bprm(bprm);
1362    if (displaced)
1363        put_files_struct(displaced);
1364    return retval;
1365
1366out:
1367    if (bprm->mm)
1368        mmput (bprm->mm);
1369
1370out_file:
1371    if (bprm->file) {
1372        allow_write_access(bprm->file);
1373        fput(bprm->file);
1374    }
1375
1376out_unmark:
1377    if (clear_in_exec)
1378        current->fs->in_exec = 0;
1379    current->in_execve = 0;
1380
1381out_free:
1382    free_bprm(bprm);
1383
1384out_files:
1385    if (displaced)
1386        reset_files_struct(displaced);
1387out_ret:
1388    return retval;
1389}
1390
1391int set_binfmt(struct linux_binfmt *new)
1392{
1393    struct linux_binfmt *old = current->binfmt;
1394
1395    if (new) {
1396        if (!try_module_get(new->module))
1397            return -1;
1398    }
1399    current->binfmt = new;
1400    if (old)
1401        module_put(old->module);
1402    return 0;
1403}
1404
1405EXPORT_SYMBOL(set_binfmt);
1406
1407/* format_corename will inspect the pattern parameter, and output a
1408 * name into corename, which must have space for at least
1409 * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
1410 */
1411static int format_corename(char *corename, long signr)
1412{
1413    const struct cred *cred = current_cred();
1414    const char *pat_ptr = core_pattern;
1415    int ispipe = (*pat_ptr == '|');
1416    char *out_ptr = corename;
1417    char *const out_end = corename + CORENAME_MAX_SIZE;
1418    int rc;
1419    int pid_in_pattern = 0;
1420
1421    /* Repeat as long as we have more pattern to process and more output
1422       space */
1423    while (*pat_ptr) {
1424        if (*pat_ptr != '%') {
1425            if (out_ptr == out_end)
1426                goto out;
1427            *out_ptr++ = *pat_ptr++;
1428        } else {
1429            switch (*++pat_ptr) {
1430            case 0:
1431                goto out;
1432            /* Double percent, output one percent */
1433            case '%':
1434                if (out_ptr == out_end)
1435                    goto out;
1436                *out_ptr++ = '%';
1437                break;
1438            /* pid */
1439            case 'p':
1440                pid_in_pattern = 1;
1441                rc = snprintf(out_ptr, out_end - out_ptr,
1442                          "%d", task_tgid_vnr(current));
1443                if (rc > out_end - out_ptr)
1444                    goto out;
1445                out_ptr += rc;
1446                break;
1447            /* uid */
1448            case 'u':
1449                rc = snprintf(out_ptr, out_end - out_ptr,
1450                          "%d", cred->uid);
1451                if (rc > out_end - out_ptr)
1452                    goto out;
1453                out_ptr += rc;
1454                break;
1455            /* gid */
1456            case 'g':
1457                rc = snprintf(out_ptr, out_end - out_ptr,
1458                          "%d", cred->gid);
1459                if (rc > out_end - out_ptr)
1460                    goto out;
1461                out_ptr += rc;
1462                break;
1463            /* signal that caused the coredump */
1464            case 's':
1465                rc = snprintf(out_ptr, out_end - out_ptr,
1466                          "%ld", signr);
1467                if (rc > out_end - out_ptr)
1468                    goto out;
1469                out_ptr += rc;
1470                break;
1471            /* UNIX time of coredump */
1472            case 't': {
1473                struct timeval tv;
1474                do_gettimeofday(&tv);
1475                rc = snprintf(out_ptr, out_end - out_ptr,
1476                          "%lu", tv.tv_sec);
1477                if (rc > out_end - out_ptr)
1478                    goto out;
1479                out_ptr += rc;
1480                break;
1481            }
1482            /* hostname */
1483            case 'h':
1484                down_read(&uts_sem);
1485                rc = snprintf(out_ptr, out_end - out_ptr,
1486                          "%s", utsname()->nodename);
1487                up_read(&uts_sem);
1488                if (rc > out_end - out_ptr)
1489                    goto out;
1490                out_ptr += rc;
1491                break;
1492            /* executable */
1493            case 'e':
1494                rc = snprintf(out_ptr, out_end - out_ptr,
1495                          "%s", current->comm);
1496                if (rc > out_end - out_ptr)
1497                    goto out;
1498                out_ptr += rc;
1499                break;
1500            /* core limit size */
1501            case 'c':
1502                rc = snprintf(out_ptr, out_end - out_ptr,
1503                          "%lu", current->signal->rlim[RLIMIT_CORE].rlim_cur);
1504                if (rc > out_end - out_ptr)
1505                    goto out;
1506                out_ptr += rc;
1507                break;
1508            default:
1509                break;
1510            }
1511            ++pat_ptr;
1512        }
1513    }
1514    /* Backward compatibility with core_uses_pid:
1515     *
1516     * If core_pattern does not include a %p (as is the default)
1517     * and core_uses_pid is set, then .%pid will be appended to
1518     * the filename. Do not do this for piped commands. */
1519    if (!ispipe && !pid_in_pattern && core_uses_pid) {
1520        rc = snprintf(out_ptr, out_end - out_ptr,
1521                  ".%d", task_tgid_vnr(current));
1522        if (rc > out_end - out_ptr)
1523            goto out;
1524        out_ptr += rc;
1525    }
1526out:
1527    *out_ptr = 0;
1528    return ispipe;
1529}
1530
1531static int zap_process(struct task_struct *start)
1532{
1533    struct task_struct *t;
1534    int nr = 0;
1535
1536    start->signal->flags = SIGNAL_GROUP_EXIT;
1537    start->signal->group_stop_count = 0;
1538
1539    t = start;
1540    do {
1541        if (t != current && t->mm) {
1542            sigaddset(&t->pending.signal, SIGKILL);
1543            signal_wake_up(t, 1);
1544            nr++;
1545        }
1546    } while_each_thread(start, t);
1547
1548    return nr;
1549}
1550
1551static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
1552                struct core_state *core_state, int exit_code)
1553{
1554    struct task_struct *g, *p;
1555    unsigned long flags;
1556    int nr = -EAGAIN;
1557
1558    spin_lock_irq(&tsk->sighand->siglock);
1559    if (!signal_group_exit(tsk->signal)) {
1560        mm->core_state = core_state;
1561        tsk->signal->group_exit_code = exit_code;
1562        nr = zap_process(tsk);
1563    }
1564    spin_unlock_irq(&tsk->sighand->siglock);
1565    if (unlikely(nr < 0))
1566        return nr;
1567
1568    if (atomic_read(&mm->mm_users) == nr + 1)
1569        goto done;
1570    /*
1571     * We should find and kill all tasks which use this mm, and we should
1572     * count them correctly into ->nr_threads. We don't take tasklist
1573     * lock, but this is safe wrt:
1574     *
1575     * fork:
1576     * None of sub-threads can fork after zap_process(leader). All
1577     * processes which were created before this point should be
1578     * visible to zap_threads() because copy_process() adds the new
1579     * process to the tail of init_task.tasks list, and lock/unlock
1580     * of ->siglock provides a memory barrier.
1581     *
1582     * do_exit:
1583     * The caller holds mm->mmap_sem. This means that the task which
1584     * uses this mm can't pass exit_mm(), so it can't exit or clear
1585     * its ->mm.
1586     *
1587     * de_thread:
1588     * It does list_replace_rcu(&leader->tasks, &current->tasks),
1589     * we must see either old or new leader, this does not matter.
1590     * However, it can change p->sighand, so lock_task_sighand(p)
1591     * must be used. Since p->mm != NULL and we hold ->mmap_sem
1592     * it can't fail.
1593     *
1594     * Note also that "g" can be the old leader with ->mm == NULL
1595     * and already unhashed and thus removed from ->thread_group.
1596     * This is OK, __unhash_process()->list_del_rcu() does not
1597     * clear the ->next pointer, we will find the new leader via
1598     * next_thread().
1599     */
1600    rcu_read_lock();
1601    for_each_process(g) {
1602        if (g == tsk->group_leader)
1603            continue;
1604        if (g->flags & PF_KTHREAD)
1605            continue;
1606        p = g;
1607        do {
1608            if (p->mm) {
1609                if (unlikely(p->mm == mm)) {
1610                    lock_task_sighand(p, &flags);
1611                    nr += zap_process(p);
1612                    unlock_task_sighand(p, &flags);
1613                }
1614                break;
1615            }
1616        } while_each_thread(g, p);
1617    }
1618    rcu_read_unlock();
1619done:
1620    atomic_set(&core_state->nr_threads, nr);
1621    return nr;
1622}
1623
1624static int coredump_wait(int exit_code, struct core_state *core_state)
1625{
1626    struct task_struct *tsk = current;
1627    struct mm_struct *mm = tsk->mm;
1628    struct completion *vfork_done;
1629    int core_waiters;
1630
1631    init_completion(&core_state->startup);
1632    core_state->dumper.task = tsk;
1633    core_state->dumper.next = NULL;
1634    core_waiters = zap_threads(tsk, mm, core_state, exit_code);
1635    up_write(&mm->mmap_sem);
1636
1637    if (unlikely(core_waiters < 0))
1638        goto fail;
1639
1640    /*
1641     * Make sure nobody is waiting for us to release the VM,
1642     * otherwise we can deadlock when we wait on each other
1643     */
1644    vfork_done = tsk->vfork_done;
1645    if (vfork_done) {
1646        tsk->vfork_done = NULL;
1647        complete(vfork_done);
1648    }
1649
1650    if (core_waiters)
1651        wait_for_completion(&core_state->startup);
1652fail:
1653    return core_waiters;
1654}
1655
1656static void coredump_finish(struct mm_struct *mm)
1657{
1658    struct core_thread *curr, *next;
1659    struct task_struct *task;
1660
1661    next = mm->core_state->dumper.next;
1662    while ((curr = next) != NULL) {
1663        next = curr->next;
1664        task = curr->task;
1665        /*
1666         * see exit_mm(), curr->task must not see
1667         * ->task == NULL before we read ->next.
1668         */
1669        smp_mb();
1670        curr->task = NULL;
1671        wake_up_process(task);
1672    }
1673
1674    mm->core_state = NULL;
1675}
1676
1677/*
1678 * set_dumpable converts traditional three-value dumpable to two flags and
1679 * stores them into mm->flags. It modifies lower two bits of mm->flags, but
1680 * these bits are not changed atomically. So get_dumpable can observe the
1681 * intermediate state. To avoid doing unexpected behavior, get get_dumpable
1682 * return either old dumpable or new one by paying attention to the order of
1683 * modifying the bits.
1684 *
1685 * dumpable | mm->flags (binary)
1686 * old new | initial interim final
1687 * ---------+-----------------------
1688 * 0 1 | 00 01 01
1689 * 0 2 | 00 10(*) 11
1690 * 1 0 | 01 00 00
1691 * 1 2 | 01 11 11
1692 * 2 0 | 11 10(*) 00
1693 * 2 1 | 11 11 01
1694 *
1695 * (*) get_dumpable regards interim value of 10 as 11.
1696 */
1697void set_dumpable(struct mm_struct *mm, int value)
1698{
1699    switch (value) {
1700    case 0:
1701        clear_bit(MMF_DUMPABLE, &mm->flags);
1702        smp_wmb();
1703        clear_bit(MMF_DUMP_SECURELY, &mm->flags);
1704        break;
1705    case 1:
1706        set_bit(MMF_DUMPABLE, &mm->flags);
1707        smp_wmb();
1708        clear_bit(MMF_DUMP_SECURELY, &mm->flags);
1709        break;
1710    case 2:
1711        set_bit(MMF_DUMP_SECURELY, &mm->flags);
1712        smp_wmb();
1713        set_bit(MMF_DUMPABLE, &mm->flags);
1714        break;
1715    }
1716}
1717
1718int get_dumpable(struct mm_struct *mm)
1719{
1720    int ret;
1721
1722    ret = mm->flags & 0x3;
1723    return (ret >= 2) ? 2 : ret;
1724}
1725
1726void do_coredump(long signr, int exit_code, struct pt_regs *regs)
1727{
1728    struct core_state core_state;
1729    char corename[CORENAME_MAX_SIZE + 1];
1730    struct mm_struct *mm = current->mm;
1731    struct linux_binfmt * binfmt;
1732    struct inode * inode;
1733    struct file * file;
1734    const struct cred *old_cred;
1735    struct cred *cred;
1736    int retval = 0;
1737    int flag = 0;
1738    int ispipe = 0;
1739    unsigned long core_limit = current->signal->rlim[RLIMIT_CORE].rlim_cur;
1740    char **helper_argv = NULL;
1741    int helper_argc = 0;
1742    char *delimit;
1743
1744    audit_core_dumps(signr);
1745
1746    binfmt = current->binfmt;
1747    if (!binfmt || !binfmt->core_dump)
1748        goto fail;
1749
1750    cred = prepare_creds();
1751    if (!cred) {
1752        retval = -ENOMEM;
1753        goto fail;
1754    }
1755
1756    down_write(&mm->mmap_sem);
1757    /*
1758     * If another thread got here first, or we are not dumpable, bail out.
1759     */
1760    if (mm->core_state || !get_dumpable(mm)) {
1761        up_write(&mm->mmap_sem);
1762        put_cred(cred);
1763        goto fail;
1764    }
1765
1766    /*
1767     * We cannot trust fsuid as being the "true" uid of the
1768     * process nor do we know its entire history. We only know it
1769     * was tainted so we dump it as root in mode 2.
1770     */
1771    if (get_dumpable(mm) == 2) { /* Setuid core dump mode */
1772        flag = O_EXCL; /* Stop rewrite attacks */
1773        cred->fsuid = 0; /* Dump root private */
1774    }
1775
1776    retval = coredump_wait(exit_code, &core_state);
1777    if (retval < 0) {
1778        put_cred(cred);
1779        goto fail;
1780    }
1781
1782    old_cred = override_creds(cred);
1783
1784    /*
1785     * Clear any false indication of pending signals that might
1786     * be seen by the filesystem code called to write the core file.
1787     */
1788    clear_thread_flag(TIF_SIGPENDING);
1789
1790    /*
1791     * lock_kernel() because format_corename() is controlled by sysctl, which
1792     * uses lock_kernel()
1793     */
1794     lock_kernel();
1795    ispipe = format_corename(corename, signr);
1796    unlock_kernel();
1797    /*
1798     * Don't bother to check the RLIMIT_CORE value if core_pattern points
1799     * to a pipe. Since we're not writing directly to the filesystem
1800     * RLIMIT_CORE doesn't really apply, as no actual core file will be
1801     * created unless the pipe reader choses to write out the core file
1802     * at which point file size limits and permissions will be imposed
1803     * as it does with any other process
1804     */
1805    if ((!ispipe) && (core_limit < binfmt->min_coredump))
1806        goto fail_unlock;
1807
1808     if (ispipe) {
1809        helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
1810        if (!helper_argv) {
1811            printk(KERN_WARNING "%s failed to allocate memory\n",
1812                   __func__);
1813            goto fail_unlock;
1814        }
1815        /* Terminate the string before the first option */
1816        delimit = strchr(corename, ' ');
1817        if (delimit)
1818            *delimit = '\0';
1819        delimit = strrchr(helper_argv[0], '/');
1820        if (delimit)
1821            delimit++;
1822        else
1823            delimit = helper_argv[0];
1824        if (!strcmp(delimit, current->comm)) {
1825            printk(KERN_NOTICE "Recursive core dump detected, "
1826                    "aborting\n");
1827            goto fail_unlock;
1828        }
1829
1830        core_limit = RLIM_INFINITY;
1831
1832        /* SIGPIPE can happen, but it's just never processed */
1833         if (call_usermodehelper_pipe(corename+1, helper_argv, NULL,
1834                &file)) {
1835             printk(KERN_INFO "Core dump to %s pipe failed\n",
1836                   corename);
1837             goto fail_unlock;
1838         }
1839     } else
1840         file = filp_open(corename,
1841                 O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
1842                 0600);
1843    if (IS_ERR(file))
1844        goto fail_unlock;
1845    inode = file->f_path.dentry->d_inode;
1846    if (inode->i_nlink > 1)
1847        goto close_fail; /* multiple links - don't dump */
1848    if (!ispipe && d_unhashed(file->f_path.dentry))
1849        goto close_fail;
1850
1851    /* AK: actually i see no reason to not allow this for named pipes etc.,
1852       but keep the previous behaviour for now. */
1853    if (!ispipe && !S_ISREG(inode->i_mode))
1854        goto close_fail;
1855    /*
1856     * Dont allow local users get cute and trick others to coredump
1857     * into their pre-created files:
1858     */
1859    if (inode->i_uid != current_fsuid())
1860        goto close_fail;
1861    if (!file->f_op)
1862        goto close_fail;
1863    if (!file->f_op->write)
1864        goto close_fail;
1865    if (!ispipe && do_truncate(file->f_path.dentry, 0, 0, file) != 0)
1866        goto close_fail;
1867
1868    retval = binfmt->core_dump(signr, regs, file, core_limit);
1869
1870    if (retval)
1871        current->signal->group_exit_code |= 0x80;
1872close_fail:
1873    filp_close(file, NULL);
1874fail_unlock:
1875    if (helper_argv)
1876        argv_free(helper_argv);
1877
1878    revert_creds(old_cred);
1879    put_cred(cred);
1880    coredump_finish(mm);
1881fail:
1882    return;
1883}
1884

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