Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/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/lsm_hooks.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  */
 45 static 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 
 56 /**
 57  * cap_capable - Determine whether a task has a particular effective capability
 58  * @cred: The credentials to use
 59  * @ns:  The user namespace in which we need the capability
 60  * @cap: The capability to check for
 61  * @audit: Whether to write an audit message or not
 62  *
 63  * Determine whether the nominated task has the specified capability amongst
 64  * its effective set, returning 0 if it does, -ve if it does not.
 65  *
 66  * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
 67  * and has_capability() functions.  That is, it has the reverse semantics:
 68  * cap_has_capability() returns 0 when a task has a capability, but the
 69  * kernel's capable() and has_capability() returns 1 for this case.
 70  */
 71 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
 72                 int cap, int audit)
 73 {
 74         struct user_namespace *ns = targ_ns;
 75 
 76         /* See if cred has the capability in the target user namespace
 77          * by examining the target user namespace and all of the target
 78          * user namespace's parents.
 79          */
 80         for (;;) {
 81                 /* Do we have the necessary capabilities? */
 82                 if (ns == cred->user_ns)
 83                         return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
 84 
 85                 /* Have we tried all of the parent namespaces? */
 86                 if (ns == &init_user_ns)
 87                         return -EPERM;
 88 
 89                 /* 
 90                  * The owner of the user namespace in the parent of the
 91                  * user namespace has all caps.
 92                  */
 93                 if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
 94                         return 0;
 95 
 96                 /*
 97                  * If you have a capability in a parent user ns, then you have
 98                  * it over all children user namespaces as well.
 99                  */
100                 ns = ns->parent;
101         }
102 
103         /* We never get here */
104 }
105 
106 /**
107  * cap_settime - Determine whether the current process may set the system clock
108  * @ts: The time to set
109  * @tz: The timezone to set
110  *
111  * Determine whether the current process may set the system clock and timezone
112  * information, returning 0 if permission granted, -ve if denied.
113  */
114 int cap_settime(const struct timespec64 *ts, const struct timezone *tz)
115 {
116         if (!capable(CAP_SYS_TIME))
117                 return -EPERM;
118         return 0;
119 }
120 
121 /**
122  * cap_ptrace_access_check - Determine whether the current process may access
123  *                         another
124  * @child: The process to be accessed
125  * @mode: The mode of attachment.
126  *
127  * If we are in the same or an ancestor user_ns and have all the target
128  * task's capabilities, then ptrace access is allowed.
129  * If we have the ptrace capability to the target user_ns, then ptrace
130  * access is allowed.
131  * Else denied.
132  *
133  * Determine whether a process may access another, returning 0 if permission
134  * granted, -ve if denied.
135  */
136 int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
137 {
138         int ret = 0;
139         const struct cred *cred, *child_cred;
140         const kernel_cap_t *caller_caps;
141 
142         rcu_read_lock();
143         cred = current_cred();
144         child_cred = __task_cred(child);
145         if (mode & PTRACE_MODE_FSCREDS)
146                 caller_caps = &cred->cap_effective;
147         else
148                 caller_caps = &cred->cap_permitted;
149         if (cred->user_ns == child_cred->user_ns &&
150             cap_issubset(child_cred->cap_permitted, *caller_caps))
151                 goto out;
152         if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
153                 goto out;
154         ret = -EPERM;
155 out:
156         rcu_read_unlock();
157         return ret;
158 }
159 
160 /**
161  * cap_ptrace_traceme - Determine whether another process may trace the current
162  * @parent: The task proposed to be the tracer
163  *
164  * If parent is in the same or an ancestor user_ns and has all current's
165  * capabilities, then ptrace access is allowed.
166  * If parent has the ptrace capability to current's user_ns, then ptrace
167  * access is allowed.
168  * Else denied.
169  *
170  * Determine whether the nominated task is permitted to trace the current
171  * process, returning 0 if permission is granted, -ve if denied.
172  */
173 int cap_ptrace_traceme(struct task_struct *parent)
174 {
175         int ret = 0;
176         const struct cred *cred, *child_cred;
177 
178         rcu_read_lock();
179         cred = __task_cred(parent);
180         child_cred = current_cred();
181         if (cred->user_ns == child_cred->user_ns &&
182             cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
183                 goto out;
184         if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE))
185                 goto out;
186         ret = -EPERM;
187 out:
188         rcu_read_unlock();
189         return ret;
190 }
191 
192 /**
193  * cap_capget - Retrieve a task's capability sets
194  * @target: The task from which to retrieve the capability sets
195  * @effective: The place to record the effective set
196  * @inheritable: The place to record the inheritable set
197  * @permitted: The place to record the permitted set
198  *
199  * This function retrieves the capabilities of the nominated task and returns
200  * them to the caller.
201  */
202 int cap_capget(struct task_struct *target, kernel_cap_t *effective,
203                kernel_cap_t *inheritable, kernel_cap_t *permitted)
204 {
205         const struct cred *cred;
206 
207         /* Derived from kernel/capability.c:sys_capget. */
208         rcu_read_lock();
209         cred = __task_cred(target);
210         *effective   = cred->cap_effective;
211         *inheritable = cred->cap_inheritable;
212         *permitted   = cred->cap_permitted;
213         rcu_read_unlock();
214         return 0;
215 }
216 
217 /*
218  * Determine whether the inheritable capabilities are limited to the old
219  * permitted set.  Returns 1 if they are limited, 0 if they are not.
220  */
221 static inline int cap_inh_is_capped(void)
222 {
223 
224         /* they are so limited unless the current task has the CAP_SETPCAP
225          * capability
226          */
227         if (cap_capable(current_cred(), current_cred()->user_ns,
228                         CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
229                 return 0;
230         return 1;
231 }
232 
233 /**
234  * cap_capset - Validate and apply proposed changes to current's capabilities
235  * @new: The proposed new credentials; alterations should be made here
236  * @old: The current task's current credentials
237  * @effective: A pointer to the proposed new effective capabilities set
238  * @inheritable: A pointer to the proposed new inheritable capabilities set
239  * @permitted: A pointer to the proposed new permitted capabilities set
240  *
241  * This function validates and applies a proposed mass change to the current
242  * process's capability sets.  The changes are made to the proposed new
243  * credentials, and assuming no error, will be committed by the caller of LSM.
244  */
245 int cap_capset(struct cred *new,
246                const struct cred *old,
247                const kernel_cap_t *effective,
248                const kernel_cap_t *inheritable,
249                const kernel_cap_t *permitted)
250 {
251         if (cap_inh_is_capped() &&
252             !cap_issubset(*inheritable,
253                           cap_combine(old->cap_inheritable,
254                                       old->cap_permitted)))
255                 /* incapable of using this inheritable set */
256                 return -EPERM;
257 
258         if (!cap_issubset(*inheritable,
259                           cap_combine(old->cap_inheritable,
260                                       old->cap_bset)))
261                 /* no new pI capabilities outside bounding set */
262                 return -EPERM;
263 
264         /* verify restrictions on target's new Permitted set */
265         if (!cap_issubset(*permitted, old->cap_permitted))
266                 return -EPERM;
267 
268         /* verify the _new_Effective_ is a subset of the _new_Permitted_ */
269         if (!cap_issubset(*effective, *permitted))
270                 return -EPERM;
271 
272         new->cap_effective   = *effective;
273         new->cap_inheritable = *inheritable;
274         new->cap_permitted   = *permitted;
275 
276         /*
277          * Mask off ambient bits that are no longer both permitted and
278          * inheritable.
279          */
280         new->cap_ambient = cap_intersect(new->cap_ambient,
281                                          cap_intersect(*permitted,
282                                                        *inheritable));
283         if (WARN_ON(!cap_ambient_invariant_ok(new)))
284                 return -EINVAL;
285         return 0;
286 }
287 
288 /*
289  * Clear proposed capability sets for execve().
290  */
291 static inline void bprm_clear_caps(struct linux_binprm *bprm)
292 {
293         cap_clear(bprm->cred->cap_permitted);
294         bprm->cap_effective = false;
295 }
296 
297 /**
298  * cap_inode_need_killpriv - Determine if inode change affects privileges
299  * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
300  *
301  * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
302  * affects the security markings on that inode, and if it is, should
303  * inode_killpriv() be invoked or the change rejected?
304  *
305  * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and
306  * -ve to deny the change.
307  */
308 int cap_inode_need_killpriv(struct dentry *dentry)
309 {
310         struct inode *inode = d_backing_inode(dentry);
311         int error;
312 
313         error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
314         return error > 0;
315 }
316 
317 /**
318  * cap_inode_killpriv - Erase the security markings on an inode
319  * @dentry: The inode/dentry to alter
320  *
321  * Erase the privilege-enhancing security markings on an inode.
322  *
323  * Returns 0 if successful, -ve on error.
324  */
325 int cap_inode_killpriv(struct dentry *dentry)
326 {
327         int error;
328 
329         error = __vfs_removexattr(dentry, XATTR_NAME_CAPS);
330         if (error == -EOPNOTSUPP)
331                 error = 0;
332         return error;
333 }
334 
335 /*
336  * Calculate the new process capability sets from the capability sets attached
337  * to a file.
338  */
339 static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
340                                           struct linux_binprm *bprm,
341                                           bool *effective,
342                                           bool *has_cap)
343 {
344         struct cred *new = bprm->cred;
345         unsigned i;
346         int ret = 0;
347 
348         if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
349                 *effective = true;
350 
351         if (caps->magic_etc & VFS_CAP_REVISION_MASK)
352                 *has_cap = true;
353 
354         CAP_FOR_EACH_U32(i) {
355                 __u32 permitted = caps->permitted.cap[i];
356                 __u32 inheritable = caps->inheritable.cap[i];
357 
358                 /*
359                  * pP' = (X & fP) | (pI & fI)
360                  * The addition of pA' is handled later.
361                  */
362                 new->cap_permitted.cap[i] =
363                         (new->cap_bset.cap[i] & permitted) |
364                         (new->cap_inheritable.cap[i] & inheritable);
365 
366                 if (permitted & ~new->cap_permitted.cap[i])
367                         /* insufficient to execute correctly */
368                         ret = -EPERM;
369         }
370 
371         /*
372          * For legacy apps, with no internal support for recognizing they
373          * do not have enough capabilities, we return an error if they are
374          * missing some "forced" (aka file-permitted) capabilities.
375          */
376         return *effective ? ret : 0;
377 }
378 
379 /*
380  * Extract the on-exec-apply capability sets for an executable file.
381  */
382 int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
383 {
384         struct inode *inode = d_backing_inode(dentry);
385         __u32 magic_etc;
386         unsigned tocopy, i;
387         int size;
388         struct vfs_cap_data caps;
389 
390         memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
391 
392         if (!inode)
393                 return -ENODATA;
394 
395         size = __vfs_getxattr((struct dentry *)dentry, inode,
396                               XATTR_NAME_CAPS, &caps, XATTR_CAPS_SZ);
397         if (size == -ENODATA || size == -EOPNOTSUPP)
398                 /* no data, that's ok */
399                 return -ENODATA;
400         if (size < 0)
401                 return size;
402 
403         if (size < sizeof(magic_etc))
404                 return -EINVAL;
405 
406         cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);
407 
408         switch (magic_etc & VFS_CAP_REVISION_MASK) {
409         case VFS_CAP_REVISION_1:
410                 if (size != XATTR_CAPS_SZ_1)
411                         return -EINVAL;
412                 tocopy = VFS_CAP_U32_1;
413                 break;
414         case VFS_CAP_REVISION_2:
415                 if (size != XATTR_CAPS_SZ_2)
416                         return -EINVAL;
417                 tocopy = VFS_CAP_U32_2;
418                 break;
419         default:
420                 return -EINVAL;
421         }
422 
423         CAP_FOR_EACH_U32(i) {
424                 if (i >= tocopy)
425                         break;
426                 cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
427                 cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
428         }
429 
430         cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
431         cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
432 
433         return 0;
434 }
435 
436 /*
437  * Attempt to get the on-exec apply capability sets for an executable file from
438  * its xattrs and, if present, apply them to the proposed credentials being
439  * constructed by execve().
440  */
441 static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap)
442 {
443         int rc = 0;
444         struct cpu_vfs_cap_data vcaps;
445 
446         bprm_clear_caps(bprm);
447 
448         if (!file_caps_enabled)
449                 return 0;
450 
451         if (!mnt_may_suid(bprm->file->f_path.mnt))
452                 return 0;
453 
454         /*
455          * This check is redundant with mnt_may_suid() but is kept to make
456          * explicit that capability bits are limited to s_user_ns and its
457          * descendants.
458          */
459         if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
460                 return 0;
461 
462         rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
463         if (rc < 0) {
464                 if (rc == -EINVAL)
465                         printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
466                                 __func__, rc, bprm->filename);
467                 else if (rc == -ENODATA)
468                         rc = 0;
469                 goto out;
470         }
471 
472         rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap);
473         if (rc == -EINVAL)
474                 printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
475                        __func__, rc, bprm->filename);
476 
477 out:
478         if (rc)
479                 bprm_clear_caps(bprm);
480 
481         return rc;
482 }
483 
484 /**
485  * cap_bprm_set_creds - Set up the proposed credentials for execve().
486  * @bprm: The execution parameters, including the proposed creds
487  *
488  * Set up the proposed credentials for a new execution context being
489  * constructed by execve().  The proposed creds in @bprm->cred is altered,
490  * which won't take effect immediately.  Returns 0 if successful, -ve on error.
491  */
492 int cap_bprm_set_creds(struct linux_binprm *bprm)
493 {
494         const struct cred *old = current_cred();
495         struct cred *new = bprm->cred;
496         bool effective, has_cap = false, is_setid;
497         int ret;
498         kuid_t root_uid;
499 
500         if (WARN_ON(!cap_ambient_invariant_ok(old)))
501                 return -EPERM;
502 
503         effective = false;
504         ret = get_file_caps(bprm, &effective, &has_cap);
505         if (ret < 0)
506                 return ret;
507 
508         root_uid = make_kuid(new->user_ns, 0);
509 
510         if (!issecure(SECURE_NOROOT)) {
511                 /*
512                  * If the legacy file capability is set, then don't set privs
513                  * for a setuid root binary run by a non-root user.  Do set it
514                  * for a root user just to cause least surprise to an admin.
515                  */
516                 if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
517                         warn_setuid_and_fcaps_mixed(bprm->filename);
518                         goto skip;
519                 }
520                 /*
521                  * To support inheritance of root-permissions and suid-root
522                  * executables under compatibility mode, we override the
523                  * capability sets for the file.
524                  *
525                  * If only the real uid is 0, we do not set the effective bit.
526                  */
527                 if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
528                         /* pP' = (cap_bset & ~0) | (pI & ~0) */
529                         new->cap_permitted = cap_combine(old->cap_bset,
530                                                          old->cap_inheritable);
531                 }
532                 if (uid_eq(new->euid, root_uid))
533                         effective = true;
534         }
535 skip:
536 
537         /* if we have fs caps, clear dangerous personality flags */
538         if (!cap_issubset(new->cap_permitted, old->cap_permitted))
539                 bprm->per_clear |= PER_CLEAR_ON_SETID;
540 
541 
542         /* Don't let someone trace a set[ug]id/setpcap binary with the revised
543          * credentials unless they have the appropriate permit.
544          *
545          * In addition, if NO_NEW_PRIVS, then ensure we get no new privs.
546          */
547         is_setid = !uid_eq(new->euid, old->uid) || !gid_eq(new->egid, old->gid);
548 
549         if ((is_setid ||
550              !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
551             bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
552                 /* downgrade; they get no more than they had, and maybe less */
553                 if (!capable(CAP_SETUID) ||
554                     (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) {
555                         new->euid = new->uid;
556                         new->egid = new->gid;
557                 }
558                 new->cap_permitted = cap_intersect(new->cap_permitted,
559                                                    old->cap_permitted);
560         }
561 
562         new->suid = new->fsuid = new->euid;
563         new->sgid = new->fsgid = new->egid;
564 
565         /* File caps or setid cancels ambient. */
566         if (has_cap || is_setid)
567                 cap_clear(new->cap_ambient);
568 
569         /*
570          * Now that we've computed pA', update pP' to give:
571          *   pP' = (X & fP) | (pI & fI) | pA'
572          */
573         new->cap_permitted = cap_combine(new->cap_permitted, new->cap_ambient);
574 
575         /*
576          * Set pE' = (fE ? pP' : pA').  Because pA' is zero if fE is set,
577          * this is the same as pE' = (fE ? pP' : 0) | pA'.
578          */
579         if (effective)
580                 new->cap_effective = new->cap_permitted;
581         else
582                 new->cap_effective = new->cap_ambient;
583 
584         if (WARN_ON(!cap_ambient_invariant_ok(new)))
585                 return -EPERM;
586 
587         bprm->cap_effective = effective;
588 
589         /*
590          * Audit candidate if current->cap_effective is set
591          *
592          * We do not bother to audit if 3 things are true:
593          *   1) cap_effective has all caps
594          *   2) we are root
595          *   3) root is supposed to have all caps (SECURE_NOROOT)
596          * Since this is just a normal root execing a process.
597          *
598          * Number 1 above might fail if you don't have a full bset, but I think
599          * that is interesting information to audit.
600          */
601         if (!cap_issubset(new->cap_effective, new->cap_ambient)) {
602                 if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
603                     !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
604                     issecure(SECURE_NOROOT)) {
605                         ret = audit_log_bprm_fcaps(bprm, new, old);
606                         if (ret < 0)
607                                 return ret;
608                 }
609         }
610 
611         new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
612 
613         if (WARN_ON(!cap_ambient_invariant_ok(new)))
614                 return -EPERM;
615 
616         return 0;
617 }
618 
619 /**
620  * cap_bprm_secureexec - Determine whether a secure execution is required
621  * @bprm: The execution parameters
622  *
623  * Determine whether a secure execution is required, return 1 if it is, and 0
624  * if it is not.
625  *
626  * The credentials have been committed by this point, and so are no longer
627  * available through @bprm->cred.
628  */
629 int cap_bprm_secureexec(struct linux_binprm *bprm)
630 {
631         const struct cred *cred = current_cred();
632         kuid_t root_uid = make_kuid(cred->user_ns, 0);
633 
634         if (!uid_eq(cred->uid, root_uid)) {
635                 if (bprm->cap_effective)
636                         return 1;
637                 if (!cap_issubset(cred->cap_permitted, cred->cap_ambient))
638                         return 1;
639         }
640 
641         return (!uid_eq(cred->euid, cred->uid) ||
642                 !gid_eq(cred->egid, cred->gid));
643 }
644 
645 /**
646  * cap_inode_setxattr - Determine whether an xattr may be altered
647  * @dentry: The inode/dentry being altered
648  * @name: The name of the xattr to be changed
649  * @value: The value that the xattr will be changed to
650  * @size: The size of value
651  * @flags: The replacement flag
652  *
653  * Determine whether an xattr may be altered or set on an inode, returning 0 if
654  * permission is granted, -ve if denied.
655  *
656  * This is used to make sure security xattrs don't get updated or set by those
657  * who aren't privileged to do so.
658  */
659 int cap_inode_setxattr(struct dentry *dentry, const char *name,
660                        const void *value, size_t size, int flags)
661 {
662         if (!strcmp(name, XATTR_NAME_CAPS)) {
663                 if (!capable(CAP_SETFCAP))
664                         return -EPERM;
665                 return 0;
666         }
667 
668         if (!strncmp(name, XATTR_SECURITY_PREFIX,
669                      sizeof(XATTR_SECURITY_PREFIX) - 1) &&
670             !capable(CAP_SYS_ADMIN))
671                 return -EPERM;
672         return 0;
673 }
674 
675 /**
676  * cap_inode_removexattr - Determine whether an xattr may be removed
677  * @dentry: The inode/dentry being altered
678  * @name: The name of the xattr to be changed
679  *
680  * Determine whether an xattr may be removed from an inode, returning 0 if
681  * permission is granted, -ve if denied.
682  *
683  * This is used to make sure security xattrs don't get removed by those who
684  * aren't privileged to remove them.
685  */
686 int cap_inode_removexattr(struct dentry *dentry, const char *name)
687 {
688         if (!strcmp(name, XATTR_NAME_CAPS)) {
689                 if (!capable(CAP_SETFCAP))
690                         return -EPERM;
691                 return 0;
692         }
693 
694         if (!strncmp(name, XATTR_SECURITY_PREFIX,
695                      sizeof(XATTR_SECURITY_PREFIX) - 1) &&
696             !capable(CAP_SYS_ADMIN))
697                 return -EPERM;
698         return 0;
699 }
700 
701 /*
702  * cap_emulate_setxuid() fixes the effective / permitted capabilities of
703  * a process after a call to setuid, setreuid, or setresuid.
704  *
705  *  1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
706  *  {r,e,s}uid != 0, the permitted and effective capabilities are
707  *  cleared.
708  *
709  *  2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
710  *  capabilities of the process are cleared.
711  *
712  *  3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
713  *  capabilities are set to the permitted capabilities.
714  *
715  *  fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
716  *  never happen.
717  *
718  *  -astor
719  *
720  * cevans - New behaviour, Oct '99
721  * A process may, via prctl(), elect to keep its capabilities when it
722  * calls setuid() and switches away from uid==0. Both permitted and
723  * effective sets will be retained.
724  * Without this change, it was impossible for a daemon to drop only some
725  * of its privilege. The call to setuid(!=0) would drop all privileges!
726  * Keeping uid 0 is not an option because uid 0 owns too many vital
727  * files..
728  * Thanks to Olaf Kirch and Peter Benie for spotting this.
729  */
730 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
731 {
732         kuid_t root_uid = make_kuid(old->user_ns, 0);
733 
734         if ((uid_eq(old->uid, root_uid) ||
735              uid_eq(old->euid, root_uid) ||
736              uid_eq(old->suid, root_uid)) &&
737             (!uid_eq(new->uid, root_uid) &&
738              !uid_eq(new->euid, root_uid) &&
739              !uid_eq(new->suid, root_uid))) {
740                 if (!issecure(SECURE_KEEP_CAPS)) {
741                         cap_clear(new->cap_permitted);
742                         cap_clear(new->cap_effective);
743                 }
744 
745                 /*
746                  * Pre-ambient programs expect setresuid to nonroot followed
747                  * by exec to drop capabilities.  We should make sure that
748                  * this remains the case.
749                  */
750                 cap_clear(new->cap_ambient);
751         }
752         if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
753                 cap_clear(new->cap_effective);
754         if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
755                 new->cap_effective = new->cap_permitted;
756 }
757 
758 /**
759  * cap_task_fix_setuid - Fix up the results of setuid() call
760  * @new: The proposed credentials
761  * @old: The current task's current credentials
762  * @flags: Indications of what has changed
763  *
764  * Fix up the results of setuid() call before the credential changes are
765  * actually applied, returning 0 to grant the changes, -ve to deny them.
766  */
767 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
768 {
769         switch (flags) {
770         case LSM_SETID_RE:
771         case LSM_SETID_ID:
772         case LSM_SETID_RES:
773                 /* juggle the capabilities to follow [RES]UID changes unless
774                  * otherwise suppressed */
775                 if (!issecure(SECURE_NO_SETUID_FIXUP))
776                         cap_emulate_setxuid(new, old);
777                 break;
778 
779         case LSM_SETID_FS:
780                 /* juggle the capabilties to follow FSUID changes, unless
781                  * otherwise suppressed
782                  *
783                  * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
784                  *          if not, we might be a bit too harsh here.
785                  */
786                 if (!issecure(SECURE_NO_SETUID_FIXUP)) {
787                         kuid_t root_uid = make_kuid(old->user_ns, 0);
788                         if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
789                                 new->cap_effective =
790                                         cap_drop_fs_set(new->cap_effective);
791 
792                         if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
793                                 new->cap_effective =
794                                         cap_raise_fs_set(new->cap_effective,
795                                                          new->cap_permitted);
796                 }
797                 break;
798 
799         default:
800                 return -EINVAL;
801         }
802 
803         return 0;
804 }
805 
806 /*
807  * Rationale: code calling task_setscheduler, task_setioprio, and
808  * task_setnice, assumes that
809  *   . if capable(cap_sys_nice), then those actions should be allowed
810  *   . if not capable(cap_sys_nice), but acting on your own processes,
811  *      then those actions should be allowed
812  * This is insufficient now since you can call code without suid, but
813  * yet with increased caps.
814  * So we check for increased caps on the target process.
815  */
816 static int cap_safe_nice(struct task_struct *p)
817 {
818         int is_subset, ret = 0;
819 
820         rcu_read_lock();
821         is_subset = cap_issubset(__task_cred(p)->cap_permitted,
822                                  current_cred()->cap_permitted);
823         if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
824                 ret = -EPERM;
825         rcu_read_unlock();
826 
827         return ret;
828 }
829 
830 /**
831  * cap_task_setscheduler - Detemine if scheduler policy change is permitted
832  * @p: The task to affect
833  *
834  * Detemine if the requested scheduler policy change is permitted for the
835  * specified task, returning 0 if permission is granted, -ve if denied.
836  */
837 int cap_task_setscheduler(struct task_struct *p)
838 {
839         return cap_safe_nice(p);
840 }
841 
842 /**
843  * cap_task_ioprio - Detemine if I/O priority change is permitted
844  * @p: The task to affect
845  * @ioprio: The I/O priority to set
846  *
847  * Detemine if the requested I/O priority change is permitted for the specified
848  * task, returning 0 if permission is granted, -ve if denied.
849  */
850 int cap_task_setioprio(struct task_struct *p, int ioprio)
851 {
852         return cap_safe_nice(p);
853 }
854 
855 /**
856  * cap_task_ioprio - Detemine if task priority change is permitted
857  * @p: The task to affect
858  * @nice: The nice value to set
859  *
860  * Detemine if the requested task priority change is permitted for the
861  * specified task, returning 0 if permission is granted, -ve if denied.
862  */
863 int cap_task_setnice(struct task_struct *p, int nice)
864 {
865         return cap_safe_nice(p);
866 }
867 
868 /*
869  * Implement PR_CAPBSET_DROP.  Attempt to remove the specified capability from
870  * the current task's bounding set.  Returns 0 on success, -ve on error.
871  */
872 static int cap_prctl_drop(unsigned long cap)
873 {
874         struct cred *new;
875 
876         if (!ns_capable(current_user_ns(), CAP_SETPCAP))
877                 return -EPERM;
878         if (!cap_valid(cap))
879                 return -EINVAL;
880 
881         new = prepare_creds();
882         if (!new)
883                 return -ENOMEM;
884         cap_lower(new->cap_bset, cap);
885         return commit_creds(new);
886 }
887 
888 /**
889  * cap_task_prctl - Implement process control functions for this security module
890  * @option: The process control function requested
891  * @arg2, @arg3, @arg4, @arg5: The argument data for this function
892  *
893  * Allow process control functions (sys_prctl()) to alter capabilities; may
894  * also deny access to other functions not otherwise implemented here.
895  *
896  * Returns 0 or +ve on success, -ENOSYS if this function is not implemented
897  * here, other -ve on error.  If -ENOSYS is returned, sys_prctl() and other LSM
898  * modules will consider performing the function.
899  */
900 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
901                    unsigned long arg4, unsigned long arg5)
902 {
903         const struct cred *old = current_cred();
904         struct cred *new;
905 
906         switch (option) {
907         case PR_CAPBSET_READ:
908                 if (!cap_valid(arg2))
909                         return -EINVAL;
910                 return !!cap_raised(old->cap_bset, arg2);
911 
912         case PR_CAPBSET_DROP:
913                 return cap_prctl_drop(arg2);
914 
915         /*
916          * The next four prctl's remain to assist with transitioning a
917          * system from legacy UID=0 based privilege (when filesystem
918          * capabilities are not in use) to a system using filesystem
919          * capabilities only - as the POSIX.1e draft intended.
920          *
921          * Note:
922          *
923          *  PR_SET_SECUREBITS =
924          *      issecure_mask(SECURE_KEEP_CAPS_LOCKED)
925          *    | issecure_mask(SECURE_NOROOT)
926          *    | issecure_mask(SECURE_NOROOT_LOCKED)
927          *    | issecure_mask(SECURE_NO_SETUID_FIXUP)
928          *    | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
929          *
930          * will ensure that the current process and all of its
931          * children will be locked into a pure
932          * capability-based-privilege environment.
933          */
934         case PR_SET_SECUREBITS:
935                 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
936                      & (old->securebits ^ arg2))                        /*[1]*/
937                     || ((old->securebits & SECURE_ALL_LOCKS & ~arg2))   /*[2]*/
938                     || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))   /*[3]*/
939                     || (cap_capable(current_cred(),
940                                     current_cred()->user_ns, CAP_SETPCAP,
941                                     SECURITY_CAP_AUDIT) != 0)           /*[4]*/
942                         /*
943                          * [1] no changing of bits that are locked
944                          * [2] no unlocking of locks
945                          * [3] no setting of unsupported bits
946                          * [4] doing anything requires privilege (go read about
947                          *     the "sendmail capabilities bug")
948                          */
949                     )
950                         /* cannot change a locked bit */
951                         return -EPERM;
952 
953                 new = prepare_creds();
954                 if (!new)
955                         return -ENOMEM;
956                 new->securebits = arg2;
957                 return commit_creds(new);
958 
959         case PR_GET_SECUREBITS:
960                 return old->securebits;
961 
962         case PR_GET_KEEPCAPS:
963                 return !!issecure(SECURE_KEEP_CAPS);
964 
965         case PR_SET_KEEPCAPS:
966                 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
967                         return -EINVAL;
968                 if (issecure(SECURE_KEEP_CAPS_LOCKED))
969                         return -EPERM;
970 
971                 new = prepare_creds();
972                 if (!new)
973                         return -ENOMEM;
974                 if (arg2)
975                         new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
976                 else
977                         new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
978                 return commit_creds(new);
979 
980         case PR_CAP_AMBIENT:
981                 if (arg2 == PR_CAP_AMBIENT_CLEAR_ALL) {
982                         if (arg3 | arg4 | arg5)
983                                 return -EINVAL;
984 
985                         new = prepare_creds();
986                         if (!new)
987                                 return -ENOMEM;
988                         cap_clear(new->cap_ambient);
989                         return commit_creds(new);
990                 }
991 
992                 if (((!cap_valid(arg3)) | arg4 | arg5))
993                         return -EINVAL;
994 
995                 if (arg2 == PR_CAP_AMBIENT_IS_SET) {
996                         return !!cap_raised(current_cred()->cap_ambient, arg3);
997                 } else if (arg2 != PR_CAP_AMBIENT_RAISE &&
998                            arg2 != PR_CAP_AMBIENT_LOWER) {
999                         return -EINVAL;
1000                 } else {
1001                         if (arg2 == PR_CAP_AMBIENT_RAISE &&
1002                             (!cap_raised(current_cred()->cap_permitted, arg3) ||
1003                              !cap_raised(current_cred()->cap_inheritable,
1004                                          arg3) ||
1005                              issecure(SECURE_NO_CAP_AMBIENT_RAISE)))
1006                                 return -EPERM;
1007 
1008                         new = prepare_creds();
1009                         if (!new)
1010                                 return -ENOMEM;
1011                         if (arg2 == PR_CAP_AMBIENT_RAISE)
1012                                 cap_raise(new->cap_ambient, arg3);
1013                         else
1014                                 cap_lower(new->cap_ambient, arg3);
1015                         return commit_creds(new);
1016                 }
1017 
1018         default:
1019                 /* No functionality available - continue with default */
1020                 return -ENOSYS;
1021         }
1022 }
1023 
1024 /**
1025  * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
1026  * @mm: The VM space in which the new mapping is to be made
1027  * @pages: The size of the mapping
1028  *
1029  * Determine whether the allocation of a new virtual mapping by the current
1030  * task is permitted, returning 1 if permission is granted, 0 if not.
1031  */
1032 int cap_vm_enough_memory(struct mm_struct *mm, long pages)
1033 {
1034         int cap_sys_admin = 0;
1035 
1036         if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
1037                         SECURITY_CAP_NOAUDIT) == 0)
1038                 cap_sys_admin = 1;
1039         return cap_sys_admin;
1040 }
1041 
1042 /*
1043  * cap_mmap_addr - check if able to map given addr
1044  * @addr: address attempting to be mapped
1045  *
1046  * If the process is attempting to map memory below dac_mmap_min_addr they need
1047  * CAP_SYS_RAWIO.  The other parameters to this function are unused by the
1048  * capability security module.  Returns 0 if this mapping should be allowed
1049  * -EPERM if not.
1050  */
1051 int cap_mmap_addr(unsigned long addr)
1052 {
1053         int ret = 0;
1054 
1055         if (addr < dac_mmap_min_addr) {
1056                 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
1057                                   SECURITY_CAP_AUDIT);
1058                 /* set PF_SUPERPRIV if it turns out we allow the low mmap */
1059                 if (ret == 0)
1060                         current->flags |= PF_SUPERPRIV;
1061         }
1062         return ret;
1063 }
1064 
1065 int cap_mmap_file(struct file *file, unsigned long reqprot,
1066                   unsigned long prot, unsigned long flags)
1067 {
1068         return 0;
1069 }
1070 
1071 #ifdef CONFIG_SECURITY
1072 
1073 struct security_hook_list capability_hooks[] = {
1074         LSM_HOOK_INIT(capable, cap_capable),
1075         LSM_HOOK_INIT(settime, cap_settime),
1076         LSM_HOOK_INIT(ptrace_access_check, cap_ptrace_access_check),
1077         LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
1078         LSM_HOOK_INIT(capget, cap_capget),
1079         LSM_HOOK_INIT(capset, cap_capset),
1080         LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds),
1081         LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec),
1082         LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
1083         LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
1084         LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),
1085         LSM_HOOK_INIT(mmap_file, cap_mmap_file),
1086         LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid),
1087         LSM_HOOK_INIT(task_prctl, cap_task_prctl),
1088         LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler),
1089         LSM_HOOK_INIT(task_setioprio, cap_task_setioprio),
1090         LSM_HOOK_INIT(task_setnice, cap_task_setnice),
1091         LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory),
1092 };
1093 
1094 void __init capability_add_hooks(void)
1095 {
1096         security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks));
1097 }
1098 
1099 #endif /* CONFIG_SECURITY */
1100 

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