Root/security/commoncap.c

1/* Common capabilities, needed by capability.o.
2 *
3 * This program is free software; you can redistribute it and/or modify
4 * it under the terms of the GNU General Public License as published by
5 * the Free Software Foundation; either version 2 of the License, or
6 * (at your option) any later version.
7 *
8 */
9
10#include <linux/capability.h>
11#include <linux/audit.h>
12#include <linux/module.h>
13#include <linux/init.h>
14#include <linux/kernel.h>
15#include <linux/security.h>
16#include <linux/file.h>
17#include <linux/mm.h>
18#include <linux/mman.h>
19#include <linux/pagemap.h>
20#include <linux/swap.h>
21#include <linux/skbuff.h>
22#include <linux/netlink.h>
23#include <linux/ptrace.h>
24#include <linux/xattr.h>
25#include <linux/hugetlb.h>
26#include <linux/mount.h>
27#include <linux/sched.h>
28#include <linux/prctl.h>
29#include <linux/securebits.h>
30#include <linux/user_namespace.h>
31#include <linux/binfmts.h>
32#include <linux/personality.h>
33
34/*
35 * If a non-root user executes a setuid-root binary in
36 * !secure(SECURE_NOROOT) mode, then we raise capabilities.
37 * However if fE is also set, then the intent is for only
38 * the file capabilities to be applied, and the setuid-root
39 * bit is left on either to change the uid (plausible) or
40 * to get full privilege on a kernel without file capabilities
41 * support. So in that case we do not raise capabilities.
42 *
43 * Warn if that happens, once per boot.
44 */
45static void warn_setuid_and_fcaps_mixed(const char *fname)
46{
47    static int warned;
48    if (!warned) {
49        printk(KERN_INFO "warning: `%s' has both setuid-root and"
50            " effective capabilities. Therefore not raising all"
51            " capabilities.\n", fname);
52        warned = 1;
53    }
54}
55
56int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
57{
58    return 0;
59}
60
61/**
62 * cap_capable - Determine whether a task has a particular effective capability
63 * @cred: The credentials to use
64 * @ns: The user namespace in which we need the capability
65 * @cap: The capability to check for
66 * @audit: Whether to write an audit message or not
67 *
68 * Determine whether the nominated task has the specified capability amongst
69 * its effective set, returning 0 if it does, -ve if it does not.
70 *
71 * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
72 * and has_capability() functions. That is, it has the reverse semantics:
73 * cap_has_capability() returns 0 when a task has a capability, but the
74 * kernel's capable() and has_capability() returns 1 for this case.
75 */
76int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
77        int cap, int audit)
78{
79    for (;;) {
80        /* The owner of the user namespace has all caps. */
81        if (targ_ns != &init_user_ns && uid_eq(targ_ns->owner, cred->euid))
82            return 0;
83
84        /* Do we have the necessary capabilities? */
85        if (targ_ns == cred->user_ns)
86            return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
87
88        /* Have we tried all of the parent namespaces? */
89        if (targ_ns == &init_user_ns)
90            return -EPERM;
91
92        /*
93         *If you have a capability in a parent user ns, then you have
94         * it over all children user namespaces as well.
95         */
96        targ_ns = targ_ns->parent;
97    }
98
99    /* We never get here */
100}
101
102/**
103 * cap_settime - Determine whether the current process may set the system clock
104 * @ts: The time to set
105 * @tz: The timezone to set
106 *
107 * Determine whether the current process may set the system clock and timezone
108 * information, returning 0 if permission granted, -ve if denied.
109 */
110int cap_settime(const struct timespec *ts, const struct timezone *tz)
111{
112    if (!capable(CAP_SYS_TIME))
113        return -EPERM;
114    return 0;
115}
116
117/**
118 * cap_ptrace_access_check - Determine whether the current process may access
119 * another
120 * @child: The process to be accessed
121 * @mode: The mode of attachment.
122 *
123 * If we are in the same or an ancestor user_ns and have all the target
124 * task's capabilities, then ptrace access is allowed.
125 * If we have the ptrace capability to the target user_ns, then ptrace
126 * access is allowed.
127 * Else denied.
128 *
129 * Determine whether a process may access another, returning 0 if permission
130 * granted, -ve if denied.
131 */
132int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
133{
134    int ret = 0;
135    const struct cred *cred, *child_cred;
136
137    rcu_read_lock();
138    cred = current_cred();
139    child_cred = __task_cred(child);
140    if (cred->user_ns == child_cred->user_ns &&
141        cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
142        goto out;
143    if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
144        goto out;
145    ret = -EPERM;
146out:
147    rcu_read_unlock();
148    return ret;
149}
150
151/**
152 * cap_ptrace_traceme - Determine whether another process may trace the current
153 * @parent: The task proposed to be the tracer
154 *
155 * If parent is in the same or an ancestor user_ns and has all current's
156 * capabilities, then ptrace access is allowed.
157 * If parent has the ptrace capability to current's user_ns, then ptrace
158 * access is allowed.
159 * Else denied.
160 *
161 * Determine whether the nominated task is permitted to trace the current
162 * process, returning 0 if permission is granted, -ve if denied.
163 */
164int cap_ptrace_traceme(struct task_struct *parent)
165{
166    int ret = 0;
167    const struct cred *cred, *child_cred;
168
169    rcu_read_lock();
170    cred = __task_cred(parent);
171    child_cred = current_cred();
172    if (cred->user_ns == child_cred->user_ns &&
173        cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
174        goto out;
175    if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE))
176        goto out;
177    ret = -EPERM;
178out:
179    rcu_read_unlock();
180    return ret;
181}
182
183/**
184 * cap_capget - Retrieve a task's capability sets
185 * @target: The task from which to retrieve the capability sets
186 * @effective: The place to record the effective set
187 * @inheritable: The place to record the inheritable set
188 * @permitted: The place to record the permitted set
189 *
190 * This function retrieves the capabilities of the nominated task and returns
191 * them to the caller.
192 */
193int cap_capget(struct task_struct *target, kernel_cap_t *effective,
194           kernel_cap_t *inheritable, kernel_cap_t *permitted)
195{
196    const struct cred *cred;
197
198    /* Derived from kernel/capability.c:sys_capget. */
199    rcu_read_lock();
200    cred = __task_cred(target);
201    *effective = cred->cap_effective;
202    *inheritable = cred->cap_inheritable;
203    *permitted = cred->cap_permitted;
204    rcu_read_unlock();
205    return 0;
206}
207
208/*
209 * Determine whether the inheritable capabilities are limited to the old
210 * permitted set. Returns 1 if they are limited, 0 if they are not.
211 */
212static inline int cap_inh_is_capped(void)
213{
214
215    /* they are so limited unless the current task has the CAP_SETPCAP
216     * capability
217     */
218    if (cap_capable(current_cred(), current_cred()->user_ns,
219            CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
220        return 0;
221    return 1;
222}
223
224/**
225 * cap_capset - Validate and apply proposed changes to current's capabilities
226 * @new: The proposed new credentials; alterations should be made here
227 * @old: The current task's current credentials
228 * @effective: A pointer to the proposed new effective capabilities set
229 * @inheritable: A pointer to the proposed new inheritable capabilities set
230 * @permitted: A pointer to the proposed new permitted capabilities set
231 *
232 * This function validates and applies a proposed mass change to the current
233 * process's capability sets. The changes are made to the proposed new
234 * credentials, and assuming no error, will be committed by the caller of LSM.
235 */
236int cap_capset(struct cred *new,
237           const struct cred *old,
238           const kernel_cap_t *effective,
239           const kernel_cap_t *inheritable,
240           const kernel_cap_t *permitted)
241{
242    if (cap_inh_is_capped() &&
243        !cap_issubset(*inheritable,
244              cap_combine(old->cap_inheritable,
245                      old->cap_permitted)))
246        /* incapable of using this inheritable set */
247        return -EPERM;
248
249    if (!cap_issubset(*inheritable,
250              cap_combine(old->cap_inheritable,
251                      old->cap_bset)))
252        /* no new pI capabilities outside bounding set */
253        return -EPERM;
254
255    /* verify restrictions on target's new Permitted set */
256    if (!cap_issubset(*permitted, old->cap_permitted))
257        return -EPERM;
258
259    /* verify the _new_Effective_ is a subset of the _new_Permitted_ */
260    if (!cap_issubset(*effective, *permitted))
261        return -EPERM;
262
263    new->cap_effective = *effective;
264    new->cap_inheritable = *inheritable;
265    new->cap_permitted = *permitted;
266    return 0;
267}
268
269/*
270 * Clear proposed capability sets for execve().
271 */
272static inline void bprm_clear_caps(struct linux_binprm *bprm)
273{
274    cap_clear(bprm->cred->cap_permitted);
275    bprm->cap_effective = false;
276}
277
278/**
279 * cap_inode_need_killpriv - Determine if inode change affects privileges
280 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
281 *
282 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
283 * affects the security markings on that inode, and if it is, should
284 * inode_killpriv() be invoked or the change rejected?
285 *
286 * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and
287 * -ve to deny the change.
288 */
289int cap_inode_need_killpriv(struct dentry *dentry)
290{
291    struct inode *inode = dentry->d_inode;
292    int error;
293
294    if (!inode->i_op->getxattr)
295           return 0;
296
297    error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0);
298    if (error <= 0)
299        return 0;
300    return 1;
301}
302
303/**
304 * cap_inode_killpriv - Erase the security markings on an inode
305 * @dentry: The inode/dentry to alter
306 *
307 * Erase the privilege-enhancing security markings on an inode.
308 *
309 * Returns 0 if successful, -ve on error.
310 */
311int cap_inode_killpriv(struct dentry *dentry)
312{
313    struct inode *inode = dentry->d_inode;
314
315    if (!inode->i_op->removexattr)
316           return 0;
317
318    return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
319}
320
321/*
322 * Calculate the new process capability sets from the capability sets attached
323 * to a file.
324 */
325static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
326                      struct linux_binprm *bprm,
327                      bool *effective,
328                      bool *has_cap)
329{
330    struct cred *new = bprm->cred;
331    unsigned i;
332    int ret = 0;
333
334    if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
335        *effective = true;
336
337    if (caps->magic_etc & VFS_CAP_REVISION_MASK)
338        *has_cap = true;
339
340    CAP_FOR_EACH_U32(i) {
341        __u32 permitted = caps->permitted.cap[i];
342        __u32 inheritable = caps->inheritable.cap[i];
343
344        /*
345         * pP' = (X & fP) | (pI & fI)
346         */
347        new->cap_permitted.cap[i] =
348            (new->cap_bset.cap[i] & permitted) |
349            (new->cap_inheritable.cap[i] & inheritable);
350
351        if (permitted & ~new->cap_permitted.cap[i])
352            /* insufficient to execute correctly */
353            ret = -EPERM;
354    }
355
356    /*
357     * For legacy apps, with no internal support for recognizing they
358     * do not have enough capabilities, we return an error if they are
359     * missing some "forced" (aka file-permitted) capabilities.
360     */
361    return *effective ? ret : 0;
362}
363
364/*
365 * Extract the on-exec-apply capability sets for an executable file.
366 */
367int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
368{
369    struct inode *inode = dentry->d_inode;
370    __u32 magic_etc;
371    unsigned tocopy, i;
372    int size;
373    struct vfs_cap_data caps;
374
375    memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
376
377    if (!inode || !inode->i_op->getxattr)
378        return -ENODATA;
379
380    size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps,
381                   XATTR_CAPS_SZ);
382    if (size == -ENODATA || size == -EOPNOTSUPP)
383        /* no data, that's ok */
384        return -ENODATA;
385    if (size < 0)
386        return size;
387
388    if (size < sizeof(magic_etc))
389        return -EINVAL;
390
391    cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);
392
393    switch (magic_etc & VFS_CAP_REVISION_MASK) {
394    case VFS_CAP_REVISION_1:
395        if (size != XATTR_CAPS_SZ_1)
396            return -EINVAL;
397        tocopy = VFS_CAP_U32_1;
398        break;
399    case VFS_CAP_REVISION_2:
400        if (size != XATTR_CAPS_SZ_2)
401            return -EINVAL;
402        tocopy = VFS_CAP_U32_2;
403        break;
404    default:
405        return -EINVAL;
406    }
407
408    CAP_FOR_EACH_U32(i) {
409        if (i >= tocopy)
410            break;
411        cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
412        cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
413    }
414
415    return 0;
416}
417
418/*
419 * Attempt to get the on-exec apply capability sets for an executable file from
420 * its xattrs and, if present, apply them to the proposed credentials being
421 * constructed by execve().
422 */
423static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap)
424{
425    struct dentry *dentry;
426    int rc = 0;
427    struct cpu_vfs_cap_data vcaps;
428
429    bprm_clear_caps(bprm);
430
431    if (!file_caps_enabled)
432        return 0;
433
434    if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID)
435        return 0;
436
437    dentry = dget(bprm->file->f_dentry);
438
439    rc = get_vfs_caps_from_disk(dentry, &vcaps);
440    if (rc < 0) {
441        if (rc == -EINVAL)
442            printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
443                __func__, rc, bprm->filename);
444        else if (rc == -ENODATA)
445            rc = 0;
446        goto out;
447    }
448
449    rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap);
450    if (rc == -EINVAL)
451        printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
452               __func__, rc, bprm->filename);
453
454out:
455    dput(dentry);
456    if (rc)
457        bprm_clear_caps(bprm);
458
459    return rc;
460}
461
462/**
463 * cap_bprm_set_creds - Set up the proposed credentials for execve().
464 * @bprm: The execution parameters, including the proposed creds
465 *
466 * Set up the proposed credentials for a new execution context being
467 * constructed by execve(). The proposed creds in @bprm->cred is altered,
468 * which won't take effect immediately. Returns 0 if successful, -ve on error.
469 */
470int cap_bprm_set_creds(struct linux_binprm *bprm)
471{
472    const struct cred *old = current_cred();
473    struct cred *new = bprm->cred;
474    bool effective, has_cap = false;
475    int ret;
476    kuid_t root_uid;
477
478    effective = false;
479    ret = get_file_caps(bprm, &effective, &has_cap);
480    if (ret < 0)
481        return ret;
482
483    root_uid = make_kuid(new->user_ns, 0);
484
485    if (!issecure(SECURE_NOROOT)) {
486        /*
487         * If the legacy file capability is set, then don't set privs
488         * for a setuid root binary run by a non-root user. Do set it
489         * for a root user just to cause least surprise to an admin.
490         */
491        if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
492            warn_setuid_and_fcaps_mixed(bprm->filename);
493            goto skip;
494        }
495        /*
496         * To support inheritance of root-permissions and suid-root
497         * executables under compatibility mode, we override the
498         * capability sets for the file.
499         *
500         * If only the real uid is 0, we do not set the effective bit.
501         */
502        if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
503            /* pP' = (cap_bset & ~0) | (pI & ~0) */
504            new->cap_permitted = cap_combine(old->cap_bset,
505                             old->cap_inheritable);
506        }
507        if (uid_eq(new->euid, root_uid))
508            effective = true;
509    }
510skip:
511
512    /* if we have fs caps, clear dangerous personality flags */
513    if (!cap_issubset(new->cap_permitted, old->cap_permitted))
514        bprm->per_clear |= PER_CLEAR_ON_SETID;
515
516
517    /* Don't let someone trace a set[ug]id/setpcap binary with the revised
518     * credentials unless they have the appropriate permit.
519     *
520     * In addition, if NO_NEW_PRIVS, then ensure we get no new privs.
521     */
522    if ((!uid_eq(new->euid, old->uid) ||
523         !gid_eq(new->egid, old->gid) ||
524         !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
525        bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
526        /* downgrade; they get no more than they had, and maybe less */
527        if (!capable(CAP_SETUID) ||
528            (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) {
529            new->euid = new->uid;
530            new->egid = new->gid;
531        }
532        new->cap_permitted = cap_intersect(new->cap_permitted,
533                           old->cap_permitted);
534    }
535
536    new->suid = new->fsuid = new->euid;
537    new->sgid = new->fsgid = new->egid;
538
539    if (effective)
540        new->cap_effective = new->cap_permitted;
541    else
542        cap_clear(new->cap_effective);
543    bprm->cap_effective = effective;
544
545    /*
546     * Audit candidate if current->cap_effective is set
547     *
548     * We do not bother to audit if 3 things are true:
549     * 1) cap_effective has all caps
550     * 2) we are root
551     * 3) root is supposed to have all caps (SECURE_NOROOT)
552     * Since this is just a normal root execing a process.
553     *
554     * Number 1 above might fail if you don't have a full bset, but I think
555     * that is interesting information to audit.
556     */
557    if (!cap_isclear(new->cap_effective)) {
558        if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
559            !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
560            issecure(SECURE_NOROOT)) {
561            ret = audit_log_bprm_fcaps(bprm, new, old);
562            if (ret < 0)
563                return ret;
564        }
565    }
566
567    new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
568    return 0;
569}
570
571/**
572 * cap_bprm_secureexec - Determine whether a secure execution is required
573 * @bprm: The execution parameters
574 *
575 * Determine whether a secure execution is required, return 1 if it is, and 0
576 * if it is not.
577 *
578 * The credentials have been committed by this point, and so are no longer
579 * available through @bprm->cred.
580 */
581int cap_bprm_secureexec(struct linux_binprm *bprm)
582{
583    const struct cred *cred = current_cred();
584    kuid_t root_uid = make_kuid(cred->user_ns, 0);
585
586    if (!uid_eq(cred->uid, root_uid)) {
587        if (bprm->cap_effective)
588            return 1;
589        if (!cap_isclear(cred->cap_permitted))
590            return 1;
591    }
592
593    return (!uid_eq(cred->euid, cred->uid) ||
594        !gid_eq(cred->egid, cred->gid));
595}
596
597/**
598 * cap_inode_setxattr - Determine whether an xattr may be altered
599 * @dentry: The inode/dentry being altered
600 * @name: The name of the xattr to be changed
601 * @value: The value that the xattr will be changed to
602 * @size: The size of value
603 * @flags: The replacement flag
604 *
605 * Determine whether an xattr may be altered or set on an inode, returning 0 if
606 * permission is granted, -ve if denied.
607 *
608 * This is used to make sure security xattrs don't get updated or set by those
609 * who aren't privileged to do so.
610 */
611int cap_inode_setxattr(struct dentry *dentry, const char *name,
612               const void *value, size_t size, int flags)
613{
614    if (!strcmp(name, XATTR_NAME_CAPS)) {
615        if (!capable(CAP_SETFCAP))
616            return -EPERM;
617        return 0;
618    }
619
620    if (!strncmp(name, XATTR_SECURITY_PREFIX,
621             sizeof(XATTR_SECURITY_PREFIX) - 1) &&
622        !capable(CAP_SYS_ADMIN))
623        return -EPERM;
624    return 0;
625}
626
627/**
628 * cap_inode_removexattr - Determine whether an xattr may be removed
629 * @dentry: The inode/dentry being altered
630 * @name: The name of the xattr to be changed
631 *
632 * Determine whether an xattr may be removed from an inode, returning 0 if
633 * permission is granted, -ve if denied.
634 *
635 * This is used to make sure security xattrs don't get removed by those who
636 * aren't privileged to remove them.
637 */
638int cap_inode_removexattr(struct dentry *dentry, const char *name)
639{
640    if (!strcmp(name, XATTR_NAME_CAPS)) {
641        if (!capable(CAP_SETFCAP))
642            return -EPERM;
643        return 0;
644    }
645
646    if (!strncmp(name, XATTR_SECURITY_PREFIX,
647             sizeof(XATTR_SECURITY_PREFIX) - 1) &&
648        !capable(CAP_SYS_ADMIN))
649        return -EPERM;
650    return 0;
651}
652
653/*
654 * cap_emulate_setxuid() fixes the effective / permitted capabilities of
655 * a process after a call to setuid, setreuid, or setresuid.
656 *
657 * 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
658 * {r,e,s}uid != 0, the permitted and effective capabilities are
659 * cleared.
660 *
661 * 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
662 * capabilities of the process are cleared.
663 *
664 * 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
665 * capabilities are set to the permitted capabilities.
666 *
667 * fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
668 * never happen.
669 *
670 * -astor
671 *
672 * cevans - New behaviour, Oct '99
673 * A process may, via prctl(), elect to keep its capabilities when it
674 * calls setuid() and switches away from uid==0. Both permitted and
675 * effective sets will be retained.
676 * Without this change, it was impossible for a daemon to drop only some
677 * of its privilege. The call to setuid(!=0) would drop all privileges!
678 * Keeping uid 0 is not an option because uid 0 owns too many vital
679 * files..
680 * Thanks to Olaf Kirch and Peter Benie for spotting this.
681 */
682static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
683{
684    kuid_t root_uid = make_kuid(old->user_ns, 0);
685
686    if ((uid_eq(old->uid, root_uid) ||
687         uid_eq(old->euid, root_uid) ||
688         uid_eq(old->suid, root_uid)) &&
689        (!uid_eq(new->uid, root_uid) &&
690         !uid_eq(new->euid, root_uid) &&
691         !uid_eq(new->suid, root_uid)) &&
692        !issecure(SECURE_KEEP_CAPS)) {
693        cap_clear(new->cap_permitted);
694        cap_clear(new->cap_effective);
695    }
696    if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
697        cap_clear(new->cap_effective);
698    if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
699        new->cap_effective = new->cap_permitted;
700}
701
702/**
703 * cap_task_fix_setuid - Fix up the results of setuid() call
704 * @new: The proposed credentials
705 * @old: The current task's current credentials
706 * @flags: Indications of what has changed
707 *
708 * Fix up the results of setuid() call before the credential changes are
709 * actually applied, returning 0 to grant the changes, -ve to deny them.
710 */
711int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
712{
713    switch (flags) {
714    case LSM_SETID_RE:
715    case LSM_SETID_ID:
716    case LSM_SETID_RES:
717        /* juggle the capabilities to follow [RES]UID changes unless
718         * otherwise suppressed */
719        if (!issecure(SECURE_NO_SETUID_FIXUP))
720            cap_emulate_setxuid(new, old);
721        break;
722
723    case LSM_SETID_FS:
724        /* juggle the capabilties to follow FSUID changes, unless
725         * otherwise suppressed
726         *
727         * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
728         * if not, we might be a bit too harsh here.
729         */
730        if (!issecure(SECURE_NO_SETUID_FIXUP)) {
731            kuid_t root_uid = make_kuid(old->user_ns, 0);
732            if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
733                new->cap_effective =
734                    cap_drop_fs_set(new->cap_effective);
735
736            if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
737                new->cap_effective =
738                    cap_raise_fs_set(new->cap_effective,
739                             new->cap_permitted);
740        }
741        break;
742
743    default:
744        return -EINVAL;
745    }
746
747    return 0;
748}
749
750/*
751 * Rationale: code calling task_setscheduler, task_setioprio, and
752 * task_setnice, assumes that
753 * . if capable(cap_sys_nice), then those actions should be allowed
754 * . if not capable(cap_sys_nice), but acting on your own processes,
755 * then those actions should be allowed
756 * This is insufficient now since you can call code without suid, but
757 * yet with increased caps.
758 * So we check for increased caps on the target process.
759 */
760static int cap_safe_nice(struct task_struct *p)
761{
762    int is_subset;
763
764    rcu_read_lock();
765    is_subset = cap_issubset(__task_cred(p)->cap_permitted,
766                 current_cred()->cap_permitted);
767    rcu_read_unlock();
768
769    if (!is_subset && !capable(CAP_SYS_NICE))
770        return -EPERM;
771    return 0;
772}
773
774/**
775 * cap_task_setscheduler - Detemine if scheduler policy change is permitted
776 * @p: The task to affect
777 *
778 * Detemine if the requested scheduler policy change is permitted for the
779 * specified task, returning 0 if permission is granted, -ve if denied.
780 */
781int cap_task_setscheduler(struct task_struct *p)
782{
783    return cap_safe_nice(p);
784}
785
786/**
787 * cap_task_ioprio - Detemine if I/O priority change is permitted
788 * @p: The task to affect
789 * @ioprio: The I/O priority to set
790 *
791 * Detemine if the requested I/O priority change is permitted for the specified
792 * task, returning 0 if permission is granted, -ve if denied.
793 */
794int cap_task_setioprio(struct task_struct *p, int ioprio)
795{
796    return cap_safe_nice(p);
797}
798
799/**
800 * cap_task_ioprio - Detemine if task priority change is permitted
801 * @p: The task to affect
802 * @nice: The nice value to set
803 *
804 * Detemine if the requested task priority change is permitted for the
805 * specified task, returning 0 if permission is granted, -ve if denied.
806 */
807int cap_task_setnice(struct task_struct *p, int nice)
808{
809    return cap_safe_nice(p);
810}
811
812/*
813 * Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from
814 * the current task's bounding set. Returns 0 on success, -ve on error.
815 */
816static long cap_prctl_drop(struct cred *new, unsigned long cap)
817{
818    if (!capable(CAP_SETPCAP))
819        return -EPERM;
820    if (!cap_valid(cap))
821        return -EINVAL;
822
823    cap_lower(new->cap_bset, cap);
824    return 0;
825}
826
827/**
828 * cap_task_prctl - Implement process control functions for this security module
829 * @option: The process control function requested
830 * @arg2, @arg3, @arg4, @arg5: The argument data for this function
831 *
832 * Allow process control functions (sys_prctl()) to alter capabilities; may
833 * also deny access to other functions not otherwise implemented here.
834 *
835 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented
836 * here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM
837 * modules will consider performing the function.
838 */
839int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
840           unsigned long arg4, unsigned long arg5)
841{
842    struct cred *new;
843    long error = 0;
844
845    new = prepare_creds();
846    if (!new)
847        return -ENOMEM;
848
849    switch (option) {
850    case PR_CAPBSET_READ:
851        error = -EINVAL;
852        if (!cap_valid(arg2))
853            goto error;
854        error = !!cap_raised(new->cap_bset, arg2);
855        goto no_change;
856
857    case PR_CAPBSET_DROP:
858        error = cap_prctl_drop(new, arg2);
859        if (error < 0)
860            goto error;
861        goto changed;
862
863    /*
864     * The next four prctl's remain to assist with transitioning a
865     * system from legacy UID=0 based privilege (when filesystem
866     * capabilities are not in use) to a system using filesystem
867     * capabilities only - as the POSIX.1e draft intended.
868     *
869     * Note:
870     *
871     * PR_SET_SECUREBITS =
872     * issecure_mask(SECURE_KEEP_CAPS_LOCKED)
873     * | issecure_mask(SECURE_NOROOT)
874     * | issecure_mask(SECURE_NOROOT_LOCKED)
875     * | issecure_mask(SECURE_NO_SETUID_FIXUP)
876     * | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
877     *
878     * will ensure that the current process and all of its
879     * children will be locked into a pure
880     * capability-based-privilege environment.
881     */
882    case PR_SET_SECUREBITS:
883        error = -EPERM;
884        if ((((new->securebits & SECURE_ALL_LOCKS) >> 1)
885             & (new->securebits ^ arg2)) /*[1]*/
886            || ((new->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
887            || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
888            || (cap_capable(current_cred(),
889                    current_cred()->user_ns, CAP_SETPCAP,
890                    SECURITY_CAP_AUDIT) != 0) /*[4]*/
891            /*
892             * [1] no changing of bits that are locked
893             * [2] no unlocking of locks
894             * [3] no setting of unsupported bits
895             * [4] doing anything requires privilege (go read about
896             * the "sendmail capabilities bug")
897             */
898            )
899            /* cannot change a locked bit */
900            goto error;
901        new->securebits = arg2;
902        goto changed;
903
904    case PR_GET_SECUREBITS:
905        error = new->securebits;
906        goto no_change;
907
908    case PR_GET_KEEPCAPS:
909        if (issecure(SECURE_KEEP_CAPS))
910            error = 1;
911        goto no_change;
912
913    case PR_SET_KEEPCAPS:
914        error = -EINVAL;
915        if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
916            goto error;
917        error = -EPERM;
918        if (issecure(SECURE_KEEP_CAPS_LOCKED))
919            goto error;
920        if (arg2)
921            new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
922        else
923            new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
924        goto changed;
925
926    default:
927        /* No functionality available - continue with default */
928        error = -ENOSYS;
929        goto error;
930    }
931
932    /* Functionality provided */
933changed:
934    return commit_creds(new);
935
936no_change:
937error:
938    abort_creds(new);
939    return error;
940}
941
942/**
943 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
944 * @mm: The VM space in which the new mapping is to be made
945 * @pages: The size of the mapping
946 *
947 * Determine whether the allocation of a new virtual mapping by the current
948 * task is permitted, returning 0 if permission is granted, -ve if not.
949 */
950int cap_vm_enough_memory(struct mm_struct *mm, long pages)
951{
952    int cap_sys_admin = 0;
953
954    if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
955            SECURITY_CAP_NOAUDIT) == 0)
956        cap_sys_admin = 1;
957    return __vm_enough_memory(mm, pages, cap_sys_admin);
958}
959
960/*
961 * cap_mmap_addr - check if able to map given addr
962 * @addr: address attempting to be mapped
963 *
964 * If the process is attempting to map memory below dac_mmap_min_addr they need
965 * CAP_SYS_RAWIO. The other parameters to this function are unused by the
966 * capability security module. Returns 0 if this mapping should be allowed
967 * -EPERM if not.
968 */
969int cap_mmap_addr(unsigned long addr)
970{
971    int ret = 0;
972
973    if (addr < dac_mmap_min_addr) {
974        ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
975                  SECURITY_CAP_AUDIT);
976        /* set PF_SUPERPRIV if it turns out we allow the low mmap */
977        if (ret == 0)
978            current->flags |= PF_SUPERPRIV;
979    }
980    return ret;
981}
982
983int cap_mmap_file(struct file *file, unsigned long reqprot,
984          unsigned long prot, unsigned long flags)
985{
986    return 0;
987}
988

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