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/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  */
 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 int 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  */
 76 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
 77                 int cap, int audit)
 78 {
 79         struct user_namespace *ns = targ_ns;
 80 
 81         /* See if cred has the capability in the target user namespace
 82          * by examining the target user namespace and all of the target
 83          * user namespace's parents.
 84          */
 85         for (;;) {
 86                 /* Do we have the necessary capabilities? */
 87                 if (ns == cred->user_ns)
 88                         return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
 89 
 90                 /* Have we tried all of the parent namespaces? */
 91                 if (ns == &init_user_ns)
 92                         return -EPERM;
 93 
 94                 /* 
 95                  * The owner of the user namespace in the parent of the
 96                  * user namespace has all caps.
 97                  */
 98                 if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
 99                         return 0;
100 
101                 /*
102                  * If you have a capability in a parent user ns, then you have
103                  * it over all children user namespaces as well.
104                  */
105                 ns = ns->parent;
106         }
107 
108         /* We never get here */
109 }
110 
111 /**
112  * cap_settime - Determine whether the current process may set the system clock
113  * @ts: The time to set
114  * @tz: The timezone to set
115  *
116  * Determine whether the current process may set the system clock and timezone
117  * information, returning 0 if permission granted, -ve if denied.
118  */
119 int cap_settime(const struct timespec *ts, const struct timezone *tz)
120 {
121         if (!capable(CAP_SYS_TIME))
122                 return -EPERM;
123         return 0;
124 }
125 
126 /**
127  * cap_ptrace_access_check - Determine whether the current process may access
128  *                         another
129  * @child: The process to be accessed
130  * @mode: The mode of attachment.
131  *
132  * If we are in the same or an ancestor user_ns and have all the target
133  * task's capabilities, then ptrace access is allowed.
134  * If we have the ptrace capability to the target user_ns, then ptrace
135  * access is allowed.
136  * Else denied.
137  *
138  * Determine whether a process may access another, returning 0 if permission
139  * granted, -ve if denied.
140  */
141 int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
142 {
143         int ret = 0;
144         const struct cred *cred, *child_cred;
145 
146         rcu_read_lock();
147         cred = current_cred();
148         child_cred = __task_cred(child);
149         if (cred->user_ns == child_cred->user_ns &&
150             cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
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         return 0;
276 }
277 
278 /*
279  * Clear proposed capability sets for execve().
280  */
281 static inline void bprm_clear_caps(struct linux_binprm *bprm)
282 {
283         cap_clear(bprm->cred->cap_permitted);
284         bprm->cap_effective = false;
285 }
286 
287 /**
288  * cap_inode_need_killpriv - Determine if inode change affects privileges
289  * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
290  *
291  * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
292  * affects the security markings on that inode, and if it is, should
293  * inode_killpriv() be invoked or the change rejected?
294  *
295  * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and
296  * -ve to deny the change.
297  */
298 int cap_inode_need_killpriv(struct dentry *dentry)
299 {
300         struct inode *inode = d_backing_inode(dentry);
301         int error;
302 
303         if (!inode->i_op->getxattr)
304                return 0;
305 
306         error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0);
307         if (error <= 0)
308                 return 0;
309         return 1;
310 }
311 
312 /**
313  * cap_inode_killpriv - Erase the security markings on an inode
314  * @dentry: The inode/dentry to alter
315  *
316  * Erase the privilege-enhancing security markings on an inode.
317  *
318  * Returns 0 if successful, -ve on error.
319  */
320 int cap_inode_killpriv(struct dentry *dentry)
321 {
322         struct inode *inode = d_backing_inode(dentry);
323 
324         if (!inode->i_op->removexattr)
325                return 0;
326 
327         return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
328 }
329 
330 /*
331  * Calculate the new process capability sets from the capability sets attached
332  * to a file.
333  */
334 static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
335                                           struct linux_binprm *bprm,
336                                           bool *effective,
337                                           bool *has_cap)
338 {
339         struct cred *new = bprm->cred;
340         unsigned i;
341         int ret = 0;
342 
343         if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
344                 *effective = true;
345 
346         if (caps->magic_etc & VFS_CAP_REVISION_MASK)
347                 *has_cap = true;
348 
349         CAP_FOR_EACH_U32(i) {
350                 __u32 permitted = caps->permitted.cap[i];
351                 __u32 inheritable = caps->inheritable.cap[i];
352 
353                 /*
354                  * pP' = (X & fP) | (pI & fI)
355                  */
356                 new->cap_permitted.cap[i] =
357                         (new->cap_bset.cap[i] & permitted) |
358                         (new->cap_inheritable.cap[i] & inheritable);
359 
360                 if (permitted & ~new->cap_permitted.cap[i])
361                         /* insufficient to execute correctly */
362                         ret = -EPERM;
363         }
364 
365         /*
366          * For legacy apps, with no internal support for recognizing they
367          * do not have enough capabilities, we return an error if they are
368          * missing some "forced" (aka file-permitted) capabilities.
369          */
370         return *effective ? ret : 0;
371 }
372 
373 /*
374  * Extract the on-exec-apply capability sets for an executable file.
375  */
376 int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
377 {
378         struct inode *inode = d_backing_inode(dentry);
379         __u32 magic_etc;
380         unsigned tocopy, i;
381         int size;
382         struct vfs_cap_data caps;
383 
384         memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
385 
386         if (!inode || !inode->i_op->getxattr)
387                 return -ENODATA;
388 
389         size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps,
390                                    XATTR_CAPS_SZ);
391         if (size == -ENODATA || size == -EOPNOTSUPP)
392                 /* no data, that's ok */
393                 return -ENODATA;
394         if (size < 0)
395                 return size;
396 
397         if (size < sizeof(magic_etc))
398                 return -EINVAL;
399 
400         cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);
401 
402         switch (magic_etc & VFS_CAP_REVISION_MASK) {
403         case VFS_CAP_REVISION_1:
404                 if (size != XATTR_CAPS_SZ_1)
405                         return -EINVAL;
406                 tocopy = VFS_CAP_U32_1;
407                 break;
408         case VFS_CAP_REVISION_2:
409                 if (size != XATTR_CAPS_SZ_2)
410                         return -EINVAL;
411                 tocopy = VFS_CAP_U32_2;
412                 break;
413         default:
414                 return -EINVAL;
415         }
416 
417         CAP_FOR_EACH_U32(i) {
418                 if (i >= tocopy)
419                         break;
420                 cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
421                 cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
422         }
423 
424         cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
425         cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
426 
427         return 0;
428 }
429 
430 /*
431  * Attempt to get the on-exec apply capability sets for an executable file from
432  * its xattrs and, if present, apply them to the proposed credentials being
433  * constructed by execve().
434  */
435 static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap)
436 {
437         int rc = 0;
438         struct cpu_vfs_cap_data vcaps;
439 
440         bprm_clear_caps(bprm);
441 
442         if (!file_caps_enabled)
443                 return 0;
444 
445         if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
446                 return 0;
447 
448         rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
449         if (rc < 0) {
450                 if (rc == -EINVAL)
451                         printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
452                                 __func__, rc, bprm->filename);
453                 else if (rc == -ENODATA)
454                         rc = 0;
455                 goto out;
456         }
457 
458         rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap);
459         if (rc == -EINVAL)
460                 printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
461                        __func__, rc, bprm->filename);
462 
463 out:
464         if (rc)
465                 bprm_clear_caps(bprm);
466 
467         return rc;
468 }
469 
470 /**
471  * cap_bprm_set_creds - Set up the proposed credentials for execve().
472  * @bprm: The execution parameters, including the proposed creds
473  *
474  * Set up the proposed credentials for a new execution context being
475  * constructed by execve().  The proposed creds in @bprm->cred is altered,
476  * which won't take effect immediately.  Returns 0 if successful, -ve on error.
477  */
478 int cap_bprm_set_creds(struct linux_binprm *bprm)
479 {
480         const struct cred *old = current_cred();
481         struct cred *new = bprm->cred;
482         bool effective, has_cap = false;
483         int ret;
484         kuid_t root_uid;
485 
486         effective = false;
487         ret = get_file_caps(bprm, &effective, &has_cap);
488         if (ret < 0)
489                 return ret;
490 
491         root_uid = make_kuid(new->user_ns, 0);
492 
493         if (!issecure(SECURE_NOROOT)) {
494                 /*
495                  * If the legacy file capability is set, then don't set privs
496                  * for a setuid root binary run by a non-root user.  Do set it
497                  * for a root user just to cause least surprise to an admin.
498                  */
499                 if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
500                         warn_setuid_and_fcaps_mixed(bprm->filename);
501                         goto skip;
502                 }
503                 /*
504                  * To support inheritance of root-permissions and suid-root
505                  * executables under compatibility mode, we override the
506                  * capability sets for the file.
507                  *
508                  * If only the real uid is 0, we do not set the effective bit.
509                  */
510                 if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
511                         /* pP' = (cap_bset & ~0) | (pI & ~0) */
512                         new->cap_permitted = cap_combine(old->cap_bset,
513                                                          old->cap_inheritable);
514                 }
515                 if (uid_eq(new->euid, root_uid))
516                         effective = true;
517         }
518 skip:
519 
520         /* if we have fs caps, clear dangerous personality flags */
521         if (!cap_issubset(new->cap_permitted, old->cap_permitted))
522                 bprm->per_clear |= PER_CLEAR_ON_SETID;
523 
524 
525         /* Don't let someone trace a set[ug]id/setpcap binary with the revised
526          * credentials unless they have the appropriate permit.
527          *
528          * In addition, if NO_NEW_PRIVS, then ensure we get no new privs.
529          */
530         if ((!uid_eq(new->euid, old->uid) ||
531              !gid_eq(new->egid, old->gid) ||
532              !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
533             bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
534                 /* downgrade; they get no more than they had, and maybe less */
535                 if (!capable(CAP_SETUID) ||
536                     (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) {
537                         new->euid = new->uid;
538                         new->egid = new->gid;
539                 }
540                 new->cap_permitted = cap_intersect(new->cap_permitted,
541                                                    old->cap_permitted);
542         }
543 
544         new->suid = new->fsuid = new->euid;
545         new->sgid = new->fsgid = new->egid;
546 
547         if (effective)
548                 new->cap_effective = new->cap_permitted;
549         else
550                 cap_clear(new->cap_effective);
551         bprm->cap_effective = effective;
552 
553         /*
554          * Audit candidate if current->cap_effective is set
555          *
556          * We do not bother to audit if 3 things are true:
557          *   1) cap_effective has all caps
558          *   2) we are root
559          *   3) root is supposed to have all caps (SECURE_NOROOT)
560          * Since this is just a normal root execing a process.
561          *
562          * Number 1 above might fail if you don't have a full bset, but I think
563          * that is interesting information to audit.
564          */
565         if (!cap_isclear(new->cap_effective)) {
566                 if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
567                     !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
568                     issecure(SECURE_NOROOT)) {
569                         ret = audit_log_bprm_fcaps(bprm, new, old);
570                         if (ret < 0)
571                                 return ret;
572                 }
573         }
574 
575         new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
576         return 0;
577 }
578 
579 /**
580  * cap_bprm_secureexec - Determine whether a secure execution is required
581  * @bprm: The execution parameters
582  *
583  * Determine whether a secure execution is required, return 1 if it is, and 0
584  * if it is not.
585  *
586  * The credentials have been committed by this point, and so are no longer
587  * available through @bprm->cred.
588  */
589 int cap_bprm_secureexec(struct linux_binprm *bprm)
590 {
591         const struct cred *cred = current_cred();
592         kuid_t root_uid = make_kuid(cred->user_ns, 0);
593 
594         if (!uid_eq(cred->uid, root_uid)) {
595                 if (bprm->cap_effective)
596                         return 1;
597                 if (!cap_isclear(cred->cap_permitted))
598                         return 1;
599         }
600 
601         return (!uid_eq(cred->euid, cred->uid) ||
602                 !gid_eq(cred->egid, cred->gid));
603 }
604 
605 /**
606  * cap_inode_setxattr - Determine whether an xattr may be altered
607  * @dentry: The inode/dentry being altered
608  * @name: The name of the xattr to be changed
609  * @value: The value that the xattr will be changed to
610  * @size: The size of value
611  * @flags: The replacement flag
612  *
613  * Determine whether an xattr may be altered or set on an inode, returning 0 if
614  * permission is granted, -ve if denied.
615  *
616  * This is used to make sure security xattrs don't get updated or set by those
617  * who aren't privileged to do so.
618  */
619 int cap_inode_setxattr(struct dentry *dentry, const char *name,
620                        const void *value, size_t size, int flags)
621 {
622         if (!strcmp(name, XATTR_NAME_CAPS)) {
623                 if (!capable(CAP_SETFCAP))
624                         return -EPERM;
625                 return 0;
626         }
627 
628         if (!strncmp(name, XATTR_SECURITY_PREFIX,
629                      sizeof(XATTR_SECURITY_PREFIX) - 1) &&
630             !capable(CAP_SYS_ADMIN))
631                 return -EPERM;
632         return 0;
633 }
634 
635 /**
636  * cap_inode_removexattr - Determine whether an xattr may be removed
637  * @dentry: The inode/dentry being altered
638  * @name: The name of the xattr to be changed
639  *
640  * Determine whether an xattr may be removed from an inode, returning 0 if
641  * permission is granted, -ve if denied.
642  *
643  * This is used to make sure security xattrs don't get removed by those who
644  * aren't privileged to remove them.
645  */
646 int cap_inode_removexattr(struct dentry *dentry, const char *name)
647 {
648         if (!strcmp(name, XATTR_NAME_CAPS)) {
649                 if (!capable(CAP_SETFCAP))
650                         return -EPERM;
651                 return 0;
652         }
653 
654         if (!strncmp(name, XATTR_SECURITY_PREFIX,
655                      sizeof(XATTR_SECURITY_PREFIX) - 1) &&
656             !capable(CAP_SYS_ADMIN))
657                 return -EPERM;
658         return 0;
659 }
660 
661 /*
662  * cap_emulate_setxuid() fixes the effective / permitted capabilities of
663  * a process after a call to setuid, setreuid, or setresuid.
664  *
665  *  1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
666  *  {r,e,s}uid != 0, the permitted and effective capabilities are
667  *  cleared.
668  *
669  *  2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
670  *  capabilities of the process are cleared.
671  *
672  *  3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
673  *  capabilities are set to the permitted capabilities.
674  *
675  *  fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
676  *  never happen.
677  *
678  *  -astor
679  *
680  * cevans - New behaviour, Oct '99
681  * A process may, via prctl(), elect to keep its capabilities when it
682  * calls setuid() and switches away from uid==0. Both permitted and
683  * effective sets will be retained.
684  * Without this change, it was impossible for a daemon to drop only some
685  * of its privilege. The call to setuid(!=0) would drop all privileges!
686  * Keeping uid 0 is not an option because uid 0 owns too many vital
687  * files..
688  * Thanks to Olaf Kirch and Peter Benie for spotting this.
689  */
690 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
691 {
692         kuid_t root_uid = make_kuid(old->user_ns, 0);
693 
694         if ((uid_eq(old->uid, root_uid) ||
695              uid_eq(old->euid, root_uid) ||
696              uid_eq(old->suid, root_uid)) &&
697             (!uid_eq(new->uid, root_uid) &&
698              !uid_eq(new->euid, root_uid) &&
699              !uid_eq(new->suid, root_uid)) &&
700             !issecure(SECURE_KEEP_CAPS)) {
701                 cap_clear(new->cap_permitted);
702                 cap_clear(new->cap_effective);
703         }
704         if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
705                 cap_clear(new->cap_effective);
706         if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
707                 new->cap_effective = new->cap_permitted;
708 }
709 
710 /**
711  * cap_task_fix_setuid - Fix up the results of setuid() call
712  * @new: The proposed credentials
713  * @old: The current task's current credentials
714  * @flags: Indications of what has changed
715  *
716  * Fix up the results of setuid() call before the credential changes are
717  * actually applied, returning 0 to grant the changes, -ve to deny them.
718  */
719 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
720 {
721         switch (flags) {
722         case LSM_SETID_RE:
723         case LSM_SETID_ID:
724         case LSM_SETID_RES:
725                 /* juggle the capabilities to follow [RES]UID changes unless
726                  * otherwise suppressed */
727                 if (!issecure(SECURE_NO_SETUID_FIXUP))
728                         cap_emulate_setxuid(new, old);
729                 break;
730 
731         case LSM_SETID_FS:
732                 /* juggle the capabilties to follow FSUID changes, unless
733                  * otherwise suppressed
734                  *
735                  * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
736                  *          if not, we might be a bit too harsh here.
737                  */
738                 if (!issecure(SECURE_NO_SETUID_FIXUP)) {
739                         kuid_t root_uid = make_kuid(old->user_ns, 0);
740                         if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
741                                 new->cap_effective =
742                                         cap_drop_fs_set(new->cap_effective);
743 
744                         if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
745                                 new->cap_effective =
746                                         cap_raise_fs_set(new->cap_effective,
747                                                          new->cap_permitted);
748                 }
749                 break;
750 
751         default:
752                 return -EINVAL;
753         }
754 
755         return 0;
756 }
757 
758 /*
759  * Rationale: code calling task_setscheduler, task_setioprio, and
760  * task_setnice, assumes that
761  *   . if capable(cap_sys_nice), then those actions should be allowed
762  *   . if not capable(cap_sys_nice), but acting on your own processes,
763  *      then those actions should be allowed
764  * This is insufficient now since you can call code without suid, but
765  * yet with increased caps.
766  * So we check for increased caps on the target process.
767  */
768 static int cap_safe_nice(struct task_struct *p)
769 {
770         int is_subset, ret = 0;
771 
772         rcu_read_lock();
773         is_subset = cap_issubset(__task_cred(p)->cap_permitted,
774                                  current_cred()->cap_permitted);
775         if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
776                 ret = -EPERM;
777         rcu_read_unlock();
778 
779         return ret;
780 }
781 
782 /**
783  * cap_task_setscheduler - Detemine if scheduler policy change is permitted
784  * @p: The task to affect
785  *
786  * Detemine if the requested scheduler policy change is permitted for the
787  * specified task, returning 0 if permission is granted, -ve if denied.
788  */
789 int cap_task_setscheduler(struct task_struct *p)
790 {
791         return cap_safe_nice(p);
792 }
793 
794 /**
795  * cap_task_ioprio - Detemine if I/O priority change is permitted
796  * @p: The task to affect
797  * @ioprio: The I/O priority to set
798  *
799  * Detemine if the requested I/O priority change is permitted for the specified
800  * task, returning 0 if permission is granted, -ve if denied.
801  */
802 int cap_task_setioprio(struct task_struct *p, int ioprio)
803 {
804         return cap_safe_nice(p);
805 }
806 
807 /**
808  * cap_task_ioprio - Detemine if task priority change is permitted
809  * @p: The task to affect
810  * @nice: The nice value to set
811  *
812  * Detemine if the requested task priority change is permitted for the
813  * specified task, returning 0 if permission is granted, -ve if denied.
814  */
815 int cap_task_setnice(struct task_struct *p, int nice)
816 {
817         return cap_safe_nice(p);
818 }
819 
820 /*
821  * Implement PR_CAPBSET_DROP.  Attempt to remove the specified capability from
822  * the current task's bounding set.  Returns 0 on success, -ve on error.
823  */
824 static int cap_prctl_drop(unsigned long cap)
825 {
826         struct cred *new;
827 
828         if (!ns_capable(current_user_ns(), CAP_SETPCAP))
829                 return -EPERM;
830         if (!cap_valid(cap))
831                 return -EINVAL;
832 
833         new = prepare_creds();
834         if (!new)
835                 return -ENOMEM;
836         cap_lower(new->cap_bset, cap);
837         return commit_creds(new);
838 }
839 
840 /**
841  * cap_task_prctl - Implement process control functions for this security module
842  * @option: The process control function requested
843  * @arg2, @arg3, @arg4, @arg5: The argument data for this function
844  *
845  * Allow process control functions (sys_prctl()) to alter capabilities; may
846  * also deny access to other functions not otherwise implemented here.
847  *
848  * Returns 0 or +ve on success, -ENOSYS if this function is not implemented
849  * here, other -ve on error.  If -ENOSYS is returned, sys_prctl() and other LSM
850  * modules will consider performing the function.
851  */
852 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
853                    unsigned long arg4, unsigned long arg5)
854 {
855         const struct cred *old = current_cred();
856         struct cred *new;
857 
858         switch (option) {
859         case PR_CAPBSET_READ:
860                 if (!cap_valid(arg2))
861                         return -EINVAL;
862                 return !!cap_raised(old->cap_bset, arg2);
863 
864         case PR_CAPBSET_DROP:
865                 return cap_prctl_drop(arg2);
866 
867         /*
868          * The next four prctl's remain to assist with transitioning a
869          * system from legacy UID=0 based privilege (when filesystem
870          * capabilities are not in use) to a system using filesystem
871          * capabilities only - as the POSIX.1e draft intended.
872          *
873          * Note:
874          *
875          *  PR_SET_SECUREBITS =
876          *      issecure_mask(SECURE_KEEP_CAPS_LOCKED)
877          *    | issecure_mask(SECURE_NOROOT)
878          *    | issecure_mask(SECURE_NOROOT_LOCKED)
879          *    | issecure_mask(SECURE_NO_SETUID_FIXUP)
880          *    | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
881          *
882          * will ensure that the current process and all of its
883          * children will be locked into a pure
884          * capability-based-privilege environment.
885          */
886         case PR_SET_SECUREBITS:
887                 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
888                      & (old->securebits ^ arg2))                        /*[1]*/
889                     || ((old->securebits & SECURE_ALL_LOCKS & ~arg2))   /*[2]*/
890                     || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))   /*[3]*/
891                     || (cap_capable(current_cred(),
892                                     current_cred()->user_ns, CAP_SETPCAP,
893                                     SECURITY_CAP_AUDIT) != 0)           /*[4]*/
894                         /*
895                          * [1] no changing of bits that are locked
896                          * [2] no unlocking of locks
897                          * [3] no setting of unsupported bits
898                          * [4] doing anything requires privilege (go read about
899                          *     the "sendmail capabilities bug")
900                          */
901                     )
902                         /* cannot change a locked bit */
903                         return -EPERM;
904 
905                 new = prepare_creds();
906                 if (!new)
907                         return -ENOMEM;
908                 new->securebits = arg2;
909                 return commit_creds(new);
910 
911         case PR_GET_SECUREBITS:
912                 return old->securebits;
913 
914         case PR_GET_KEEPCAPS:
915                 return !!issecure(SECURE_KEEP_CAPS);
916 
917         case PR_SET_KEEPCAPS:
918                 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
919                         return -EINVAL;
920                 if (issecure(SECURE_KEEP_CAPS_LOCKED))
921                         return -EPERM;
922 
923                 new = prepare_creds();
924                 if (!new)
925                         return -ENOMEM;
926                 if (arg2)
927                         new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
928                 else
929                         new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
930                 return commit_creds(new);
931 
932         default:
933                 /* No functionality available - continue with default */
934                 return -ENOSYS;
935         }
936 }
937 
938 /**
939  * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
940  * @mm: The VM space in which the new mapping is to be made
941  * @pages: The size of the mapping
942  *
943  * Determine whether the allocation of a new virtual mapping by the current
944  * task is permitted, returning 0 if permission is granted, -ve if not.
945  */
946 int cap_vm_enough_memory(struct mm_struct *mm, long pages)
947 {
948         int cap_sys_admin = 0;
949 
950         if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
951                         SECURITY_CAP_NOAUDIT) == 0)
952                 cap_sys_admin = 1;
953         return __vm_enough_memory(mm, pages, cap_sys_admin);
954 }
955 
956 /*
957  * cap_mmap_addr - check if able to map given addr
958  * @addr: address attempting to be mapped
959  *
960  * If the process is attempting to map memory below dac_mmap_min_addr they need
961  * CAP_SYS_RAWIO.  The other parameters to this function are unused by the
962  * capability security module.  Returns 0 if this mapping should be allowed
963  * -EPERM if not.
964  */
965 int cap_mmap_addr(unsigned long addr)
966 {
967         int ret = 0;
968 
969         if (addr < dac_mmap_min_addr) {
970                 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
971                                   SECURITY_CAP_AUDIT);
972                 /* set PF_SUPERPRIV if it turns out we allow the low mmap */
973                 if (ret == 0)
974                         current->flags |= PF_SUPERPRIV;
975         }
976         return ret;
977 }
978 
979 int cap_mmap_file(struct file *file, unsigned long reqprot,
980                   unsigned long prot, unsigned long flags)
981 {
982         return 0;
983 }
984 

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