Root/fs/binfmt_misc.c

1/*
2 * binfmt_misc.c
3 *
4 * Copyright (C) 1997 Richard G√ľnther
5 *
6 * binfmt_misc detects binaries via a magic or filename extension and invokes
7 * a specified wrapper. This should obsolete binfmt_java, binfmt_em86 and
8 * binfmt_mz.
9 *
10 * 1997-04-25 first version
11 * [...]
12 * 1997-05-19 cleanup
13 * 1997-06-26 hpa: pass the real filename rather than argv[0]
14 * 1997-06-30 minor cleanup
15 * 1997-08-09 removed extension stripping, locking cleanup
16 * 2001-02-28 AV: rewritten into something that resembles C. Original didn't.
17 */
18
19#include <linux/module.h>
20#include <linux/init.h>
21#include <linux/sched.h>
22#include <linux/binfmts.h>
23#include <linux/slab.h>
24#include <linux/ctype.h>
25#include <linux/file.h>
26#include <linux/pagemap.h>
27#include <linux/namei.h>
28#include <linux/mount.h>
29#include <linux/syscalls.h>
30#include <linux/fs.h>
31
32#include <asm/uaccess.h>
33
34enum {
35    VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
36};
37
38static LIST_HEAD(entries);
39static int enabled = 1;
40
41enum {Enabled, Magic};
42#define MISC_FMT_PRESERVE_ARGV0 (1<<31)
43#define MISC_FMT_OPEN_BINARY (1<<30)
44#define MISC_FMT_CREDENTIALS (1<<29)
45
46typedef struct {
47    struct list_head list;
48    unsigned long flags; /* type, status, etc. */
49    int offset; /* offset of magic */
50    int size; /* size of magic/mask */
51    char *magic; /* magic or filename extension */
52    char *mask; /* mask, NULL for exact match */
53    char *interpreter; /* filename of interpreter */
54    char *name;
55    struct dentry *dentry;
56} Node;
57
58static DEFINE_RWLOCK(entries_lock);
59static struct file_system_type bm_fs_type;
60static struct vfsmount *bm_mnt;
61static int entry_count;
62
63/*
64 * Check if we support the binfmt
65 * if we do, return the node, else NULL
66 * locking is done in load_misc_binary
67 */
68static Node *check_file(struct linux_binprm *bprm)
69{
70    char *p = strrchr(bprm->interp, '.');
71    struct list_head *l;
72
73    list_for_each(l, &entries) {
74        Node *e = list_entry(l, Node, list);
75        char *s;
76        int j;
77
78        if (!test_bit(Enabled, &e->flags))
79            continue;
80
81        if (!test_bit(Magic, &e->flags)) {
82            if (p && !strcmp(e->magic, p + 1))
83                return e;
84            continue;
85        }
86
87        s = bprm->buf + e->offset;
88        if (e->mask) {
89            for (j = 0; j < e->size; j++)
90                if ((*s++ ^ e->magic[j]) & e->mask[j])
91                    break;
92        } else {
93            for (j = 0; j < e->size; j++)
94                if ((*s++ ^ e->magic[j]))
95                    break;
96        }
97        if (j == e->size)
98            return e;
99    }
100    return NULL;
101}
102
103/*
104 * the loader itself
105 */
106static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
107{
108    Node *fmt;
109    struct file * interp_file = NULL;
110    char iname[BINPRM_BUF_SIZE];
111    char *iname_addr = iname;
112    int retval;
113    int fd_binary = -1;
114
115    retval = -ENOEXEC;
116    if (!enabled)
117        goto _ret;
118
119    retval = -ENOEXEC;
120    if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
121        goto _ret;
122
123    /* to keep locking time low, we copy the interpreter string */
124    read_lock(&entries_lock);
125    fmt = check_file(bprm);
126    if (fmt)
127        strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
128    read_unlock(&entries_lock);
129    if (!fmt)
130        goto _ret;
131
132    if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
133        retval = remove_arg_zero(bprm);
134        if (retval)
135            goto _ret;
136    }
137
138    if (fmt->flags & MISC_FMT_OPEN_BINARY) {
139
140        /* if the binary should be opened on behalf of the
141         * interpreter than keep it open and assign descriptor
142         * to it */
143         fd_binary = get_unused_fd();
144         if (fd_binary < 0) {
145             retval = fd_binary;
146             goto _ret;
147         }
148         fd_install(fd_binary, bprm->file);
149
150        /* if the binary is not readable than enforce mm->dumpable=0
151           regardless of the interpreter's permissions */
152        if (file_permission(bprm->file, MAY_READ))
153            bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
154
155        allow_write_access(bprm->file);
156        bprm->file = NULL;
157
158        /* mark the bprm that fd should be passed to interp */
159        bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
160        bprm->interp_data = fd_binary;
161
162     } else {
163         allow_write_access(bprm->file);
164         fput(bprm->file);
165         bprm->file = NULL;
166     }
167    /* make argv[1] be the path to the binary */
168    retval = copy_strings_kernel (1, &bprm->interp, bprm);
169    if (retval < 0)
170        goto _error;
171    bprm->argc++;
172
173    /* add the interp as argv[0] */
174    retval = copy_strings_kernel (1, &iname_addr, bprm);
175    if (retval < 0)
176        goto _error;
177    bprm->argc ++;
178
179    bprm->interp = iname; /* for binfmt_script */
180
181    interp_file = open_exec (iname);
182    retval = PTR_ERR (interp_file);
183    if (IS_ERR (interp_file))
184        goto _error;
185
186    bprm->file = interp_file;
187    if (fmt->flags & MISC_FMT_CREDENTIALS) {
188        /*
189         * No need to call prepare_binprm(), it's already been
190         * done. bprm->buf is stale, update from interp_file.
191         */
192        memset(bprm->buf, 0, BINPRM_BUF_SIZE);
193        retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
194    } else
195        retval = prepare_binprm (bprm);
196
197    if (retval < 0)
198        goto _error;
199
200    bprm->recursion_depth++;
201
202    retval = search_binary_handler (bprm, regs);
203    if (retval < 0)
204        goto _error;
205
206_ret:
207    return retval;
208_error:
209    if (fd_binary > 0)
210        sys_close(fd_binary);
211    bprm->interp_flags = 0;
212    bprm->interp_data = 0;
213    goto _ret;
214}
215
216/* Command parsers */
217
218/*
219 * parses and copies one argument enclosed in del from *sp to *dp,
220 * recognising the \x special.
221 * returns pointer to the copied argument or NULL in case of an
222 * error (and sets err) or null argument length.
223 */
224static char *scanarg(char *s, char del)
225{
226    char c;
227
228    while ((c = *s++) != del) {
229        if (c == '\\' && *s == 'x') {
230            s++;
231            if (!isxdigit(*s++))
232                return NULL;
233            if (!isxdigit(*s++))
234                return NULL;
235        }
236    }
237    return s;
238}
239
240static int unquote(char *from)
241{
242    char c = 0, *s = from, *p = from;
243
244    while ((c = *s++) != '\0') {
245        if (c == '\\' && *s == 'x') {
246            s++;
247            c = toupper(*s++);
248            *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
249            c = toupper(*s++);
250            *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
251            continue;
252        }
253        *p++ = c;
254    }
255    return p - from;
256}
257
258static char * check_special_flags (char * sfs, Node * e)
259{
260    char * p = sfs;
261    int cont = 1;
262
263    /* special flags */
264    while (cont) {
265        switch (*p) {
266            case 'P':
267                p++;
268                e->flags |= MISC_FMT_PRESERVE_ARGV0;
269                break;
270            case 'O':
271                p++;
272                e->flags |= MISC_FMT_OPEN_BINARY;
273                break;
274            case 'C':
275                p++;
276                /* this flags also implies the
277                   open-binary flag */
278                e->flags |= (MISC_FMT_CREDENTIALS |
279                        MISC_FMT_OPEN_BINARY);
280                break;
281            default:
282                cont = 0;
283        }
284    }
285
286    return p;
287}
288/*
289 * This registers a new binary format, it recognises the syntax
290 * ':name:type:offset:magic:mask:interpreter:flags'
291 * where the ':' is the IFS, that can be chosen with the first char
292 */
293static Node *create_entry(const char __user *buffer, size_t count)
294{
295    Node *e;
296    int memsize, err;
297    char *buf, *p;
298    char del;
299
300    /* some sanity checks */
301    err = -EINVAL;
302    if ((count < 11) || (count > 256))
303        goto out;
304
305    err = -ENOMEM;
306    memsize = sizeof(Node) + count + 8;
307    e = kmalloc(memsize, GFP_USER);
308    if (!e)
309        goto out;
310
311    p = buf = (char *)e + sizeof(Node);
312
313    memset(e, 0, sizeof(Node));
314    if (copy_from_user(buf, buffer, count))
315        goto Efault;
316
317    del = *p++; /* delimeter */
318
319    memset(buf+count, del, 8);
320
321    e->name = p;
322    p = strchr(p, del);
323    if (!p)
324        goto Einval;
325    *p++ = '\0';
326    if (!e->name[0] ||
327        !strcmp(e->name, ".") ||
328        !strcmp(e->name, "..") ||
329        strchr(e->name, '/'))
330        goto Einval;
331    switch (*p++) {
332        case 'E': e->flags = 1<<Enabled; break;
333        case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
334        default: goto Einval;
335    }
336    if (*p++ != del)
337        goto Einval;
338    if (test_bit(Magic, &e->flags)) {
339        char *s = strchr(p, del);
340        if (!s)
341            goto Einval;
342        *s++ = '\0';
343        e->offset = simple_strtoul(p, &p, 10);
344        if (*p++)
345            goto Einval;
346        e->magic = p;
347        p = scanarg(p, del);
348        if (!p)
349            goto Einval;
350        p[-1] = '\0';
351        if (!e->magic[0])
352            goto Einval;
353        e->mask = p;
354        p = scanarg(p, del);
355        if (!p)
356            goto Einval;
357        p[-1] = '\0';
358        if (!e->mask[0])
359            e->mask = NULL;
360        e->size = unquote(e->magic);
361        if (e->mask && unquote(e->mask) != e->size)
362            goto Einval;
363        if (e->size + e->offset > BINPRM_BUF_SIZE)
364            goto Einval;
365    } else {
366        p = strchr(p, del);
367        if (!p)
368            goto Einval;
369        *p++ = '\0';
370        e->magic = p;
371        p = strchr(p, del);
372        if (!p)
373            goto Einval;
374        *p++ = '\0';
375        if (!e->magic[0] || strchr(e->magic, '/'))
376            goto Einval;
377        p = strchr(p, del);
378        if (!p)
379            goto Einval;
380        *p++ = '\0';
381    }
382    e->interpreter = p;
383    p = strchr(p, del);
384    if (!p)
385        goto Einval;
386    *p++ = '\0';
387    if (!e->interpreter[0])
388        goto Einval;
389
390
391    p = check_special_flags (p, e);
392
393    if (*p == '\n')
394        p++;
395    if (p != buf + count)
396        goto Einval;
397    return e;
398
399out:
400    return ERR_PTR(err);
401
402Efault:
403    kfree(e);
404    return ERR_PTR(-EFAULT);
405Einval:
406    kfree(e);
407    return ERR_PTR(-EINVAL);
408}
409
410/*
411 * Set status of entry/binfmt_misc:
412 * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
413 */
414static int parse_command(const char __user *buffer, size_t count)
415{
416    char s[4];
417
418    if (!count)
419        return 0;
420    if (count > 3)
421        return -EINVAL;
422    if (copy_from_user(s, buffer, count))
423        return -EFAULT;
424    if (s[count-1] == '\n')
425        count--;
426    if (count == 1 && s[0] == '0')
427        return 1;
428    if (count == 1 && s[0] == '1')
429        return 2;
430    if (count == 2 && s[0] == '-' && s[1] == '1')
431        return 3;
432    return -EINVAL;
433}
434
435/* generic stuff */
436
437static void entry_status(Node *e, char *page)
438{
439    char *dp;
440    char *status = "disabled";
441    const char * flags = "flags: ";
442
443    if (test_bit(Enabled, &e->flags))
444        status = "enabled";
445
446    if (!VERBOSE_STATUS) {
447        sprintf(page, "%s\n", status);
448        return;
449    }
450
451    sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
452    dp = page + strlen(page);
453
454    /* print the special flags */
455    sprintf (dp, "%s", flags);
456    dp += strlen (flags);
457    if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
458        *dp ++ = 'P';
459    }
460    if (e->flags & MISC_FMT_OPEN_BINARY) {
461        *dp ++ = 'O';
462    }
463    if (e->flags & MISC_FMT_CREDENTIALS) {
464        *dp ++ = 'C';
465    }
466    *dp ++ = '\n';
467
468
469    if (!test_bit(Magic, &e->flags)) {
470        sprintf(dp, "extension .%s\n", e->magic);
471    } else {
472        int i;
473
474        sprintf(dp, "offset %i\nmagic ", e->offset);
475        dp = page + strlen(page);
476        for (i = 0; i < e->size; i++) {
477            sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
478            dp += 2;
479        }
480        if (e->mask) {
481            sprintf(dp, "\nmask ");
482            dp += 6;
483            for (i = 0; i < e->size; i++) {
484                sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
485                dp += 2;
486            }
487        }
488        *dp++ = '\n';
489        *dp = '\0';
490    }
491}
492
493static struct inode *bm_get_inode(struct super_block *sb, int mode)
494{
495    struct inode * inode = new_inode(sb);
496
497    if (inode) {
498        inode->i_mode = mode;
499        inode->i_atime = inode->i_mtime = inode->i_ctime =
500            current_fs_time(inode->i_sb);
501    }
502    return inode;
503}
504
505static void bm_clear_inode(struct inode *inode)
506{
507    kfree(inode->i_private);
508}
509
510static void kill_node(Node *e)
511{
512    struct dentry *dentry;
513
514    write_lock(&entries_lock);
515    dentry = e->dentry;
516    if (dentry) {
517        list_del_init(&e->list);
518        e->dentry = NULL;
519    }
520    write_unlock(&entries_lock);
521
522    if (dentry) {
523        dentry->d_inode->i_nlink--;
524        d_drop(dentry);
525        dput(dentry);
526        simple_release_fs(&bm_mnt, &entry_count);
527    }
528}
529
530/* /<entry> */
531
532static ssize_t
533bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
534{
535    Node *e = file->f_path.dentry->d_inode->i_private;
536    ssize_t res;
537    char *page;
538
539    if (!(page = (char*) __get_free_page(GFP_KERNEL)))
540        return -ENOMEM;
541
542    entry_status(e, page);
543
544    res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
545
546    free_page((unsigned long) page);
547    return res;
548}
549
550static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
551                size_t count, loff_t *ppos)
552{
553    struct dentry *root;
554    Node *e = file->f_path.dentry->d_inode->i_private;
555    int res = parse_command(buffer, count);
556
557    switch (res) {
558        case 1: clear_bit(Enabled, &e->flags);
559            break;
560        case 2: set_bit(Enabled, &e->flags);
561            break;
562        case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
563            mutex_lock(&root->d_inode->i_mutex);
564
565            kill_node(e);
566
567            mutex_unlock(&root->d_inode->i_mutex);
568            dput(root);
569            break;
570        default: return res;
571    }
572    return count;
573}
574
575static const struct file_operations bm_entry_operations = {
576    .read = bm_entry_read,
577    .write = bm_entry_write,
578};
579
580/* /register */
581
582static ssize_t bm_register_write(struct file *file, const char __user *buffer,
583                   size_t count, loff_t *ppos)
584{
585    Node *e;
586    struct inode *inode;
587    struct dentry *root, *dentry;
588    struct super_block *sb = file->f_path.mnt->mnt_sb;
589    int err = 0;
590
591    e = create_entry(buffer, count);
592
593    if (IS_ERR(e))
594        return PTR_ERR(e);
595
596    root = dget(sb->s_root);
597    mutex_lock(&root->d_inode->i_mutex);
598    dentry = lookup_one_len(e->name, root, strlen(e->name));
599    err = PTR_ERR(dentry);
600    if (IS_ERR(dentry))
601        goto out;
602
603    err = -EEXIST;
604    if (dentry->d_inode)
605        goto out2;
606
607    inode = bm_get_inode(sb, S_IFREG | 0644);
608
609    err = -ENOMEM;
610    if (!inode)
611        goto out2;
612
613    err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
614    if (err) {
615        iput(inode);
616        inode = NULL;
617        goto out2;
618    }
619
620    e->dentry = dget(dentry);
621    inode->i_private = e;
622    inode->i_fop = &bm_entry_operations;
623
624    d_instantiate(dentry, inode);
625    write_lock(&entries_lock);
626    list_add(&e->list, &entries);
627    write_unlock(&entries_lock);
628
629    err = 0;
630out2:
631    dput(dentry);
632out:
633    mutex_unlock(&root->d_inode->i_mutex);
634    dput(root);
635
636    if (err) {
637        kfree(e);
638        return -EINVAL;
639    }
640    return count;
641}
642
643static const struct file_operations bm_register_operations = {
644    .write = bm_register_write,
645};
646
647/* /status */
648
649static ssize_t
650bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
651{
652    char *s = enabled ? "enabled\n" : "disabled\n";
653
654    return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
655}
656
657static ssize_t bm_status_write(struct file * file, const char __user * buffer,
658        size_t count, loff_t *ppos)
659{
660    int res = parse_command(buffer, count);
661    struct dentry *root;
662
663    switch (res) {
664        case 1: enabled = 0; break;
665        case 2: enabled = 1; break;
666        case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
667            mutex_lock(&root->d_inode->i_mutex);
668
669            while (!list_empty(&entries))
670                kill_node(list_entry(entries.next, Node, list));
671
672            mutex_unlock(&root->d_inode->i_mutex);
673            dput(root);
674        default: return res;
675    }
676    return count;
677}
678
679static const struct file_operations bm_status_operations = {
680    .read = bm_status_read,
681    .write = bm_status_write,
682};
683
684/* Superblock handling */
685
686static const struct super_operations s_ops = {
687    .statfs = simple_statfs,
688    .clear_inode = bm_clear_inode,
689};
690
691static int bm_fill_super(struct super_block * sb, void * data, int silent)
692{
693    static struct tree_descr bm_files[] = {
694        [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
695        [3] = {"register", &bm_register_operations, S_IWUSR},
696        /* last one */ {""}
697    };
698    int err = simple_fill_super(sb, 0x42494e4d, bm_files);
699    if (!err)
700        sb->s_op = &s_ops;
701    return err;
702}
703
704static int bm_get_sb(struct file_system_type *fs_type,
705    int flags, const char *dev_name, void *data, struct vfsmount *mnt)
706{
707    return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
708}
709
710static struct linux_binfmt misc_format = {
711    .module = THIS_MODULE,
712    .load_binary = load_misc_binary,
713};
714
715static struct file_system_type bm_fs_type = {
716    .owner = THIS_MODULE,
717    .name = "binfmt_misc",
718    .get_sb = bm_get_sb,
719    .kill_sb = kill_litter_super,
720};
721
722static int __init init_misc_binfmt(void)
723{
724    int err = register_filesystem(&bm_fs_type);
725    if (!err) {
726        err = register_binfmt(&misc_format);
727        if (err)
728            unregister_filesystem(&bm_fs_type);
729    }
730    return err;
731}
732
733static void __exit exit_misc_binfmt(void)
734{
735    unregister_binfmt(&misc_format);
736    unregister_filesystem(&bm_fs_type);
737}
738
739core_initcall(init_misc_binfmt);
740module_exit(exit_misc_binfmt);
741MODULE_LICENSE("GPL");
742

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