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 */
warn_setuid_and_fcaps_mixed(const char * fname)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
cap_netlink_send(struct sock * sk,struct sk_buff * skb)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 */
cap_capable(const struct cred * cred,struct user_namespace * targ_ns,int cap,int audit)76 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
77 int cap, int audit)
78 {
79 for (;;) {
80 /* The creator of the user namespace has all caps. */
81 if (targ_ns != &init_user_ns && targ_ns->creator == cred->user)
82 return 0;
83
84 /* Do we have the necessary capabilities? */
85 if (targ_ns == cred->user->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->creator->user_ns;
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 */
cap_settime(const struct timespec * ts,const struct timezone * tz)110 int 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 */
cap_ptrace_access_check(struct task_struct * child,unsigned int mode)132 int 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->user_ns == child_cred->user->user_ns &&
141 cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
142 goto out;
143 if (ns_capable(child_cred->user->user_ns, CAP_SYS_PTRACE))
144 goto out;
145 ret = -EPERM;
146 out:
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 */
cap_ptrace_traceme(struct task_struct * parent)164 int 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->user_ns == child_cred->user->user_ns &&
173 cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
174 goto out;
175 if (has_ns_capability(parent, child_cred->user->user_ns, CAP_SYS_PTRACE))
176 goto out;
177 ret = -EPERM;
178 out:
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 */
cap_capget(struct task_struct * target,kernel_cap_t * effective,kernel_cap_t * inheritable,kernel_cap_t * permitted)193 int 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 */
cap_inh_is_capped(void)212 static 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->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 */
cap_capset(struct cred * new,const struct cred * old,const kernel_cap_t * effective,const kernel_cap_t * inheritable,const kernel_cap_t * permitted)236 int 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 */
bprm_clear_caps(struct linux_binprm * bprm)272 static 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 */
cap_inode_need_killpriv(struct dentry * dentry)289 int 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 */
cap_inode_killpriv(struct dentry * dentry)311 int 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 */
bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data * caps,struct linux_binprm * bprm,bool * effective,bool * has_cap)325 static 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 */
get_vfs_caps_from_disk(const struct dentry * dentry,struct cpu_vfs_cap_data * cpu_caps)367 int 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 */
get_file_caps(struct linux_binprm * bprm,bool * effective,bool * has_cap)423 static 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
454 out:
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 */
cap_bprm_set_creds(struct linux_binprm * bprm)470 int 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
477 effective = false;
478 ret = get_file_caps(bprm, &effective, &has_cap);
479 if (ret < 0)
480 return ret;
481
482 if (!issecure(SECURE_NOROOT)) {
483 /*
484 * If the legacy file capability is set, then don't set privs
485 * for a setuid root binary run by a non-root user. Do set it
486 * for a root user just to cause least surprise to an admin.
487 */
488 if (has_cap && new->uid != 0 && new->euid == 0) {
489 warn_setuid_and_fcaps_mixed(bprm->filename);
490 goto skip;
491 }
492 /*
493 * To support inheritance of root-permissions and suid-root
494 * executables under compatibility mode, we override the
495 * capability sets for the file.
496 *
497 * If only the real uid is 0, we do not set the effective bit.
498 */
499 if (new->euid == 0 || new->uid == 0) {
500 /* pP' = (cap_bset & ~0) | (pI & ~0) */
501 new->cap_permitted = cap_combine(old->cap_bset,
502 old->cap_inheritable);
503 }
504 if (new->euid == 0)
505 effective = true;
506 }
507 skip:
508
509 /* if we have fs caps, clear dangerous personality flags */
510 if (!cap_issubset(new->cap_permitted, old->cap_permitted))
511 bprm->per_clear |= PER_CLEAR_ON_SETID;
512
513
514 /* Don't let someone trace a set[ug]id/setpcap binary with the revised
515 * credentials unless they have the appropriate permit
516 */
517 if ((new->euid != old->uid ||
518 new->egid != old->gid ||
519 !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
520 bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
521 /* downgrade; they get no more than they had, and maybe less */
522 if (!capable(CAP_SETUID)) {
523 new->euid = new->uid;
524 new->egid = new->gid;
525 }
526 new->cap_permitted = cap_intersect(new->cap_permitted,
527 old->cap_permitted);
528 }
529
530 new->suid = new->fsuid = new->euid;
531 new->sgid = new->fsgid = new->egid;
532
533 if (effective)
534 new->cap_effective = new->cap_permitted;
535 else
536 cap_clear(new->cap_effective);
537 bprm->cap_effective = effective;
538
539 /*
540 * Audit candidate if current->cap_effective is set
541 *
542 * We do not bother to audit if 3 things are true:
543 * 1) cap_effective has all caps
544 * 2) we are root
545 * 3) root is supposed to have all caps (SECURE_NOROOT)
546 * Since this is just a normal root execing a process.
547 *
548 * Number 1 above might fail if you don't have a full bset, but I think
549 * that is interesting information to audit.
550 */
551 if (!cap_isclear(new->cap_effective)) {
552 if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
553 new->euid != 0 || new->uid != 0 ||
554 issecure(SECURE_NOROOT)) {
555 ret = audit_log_bprm_fcaps(bprm, new, old);
556 if (ret < 0)
557 return ret;
558 }
559 }
560
561 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
562 return 0;
563 }
564
565 /**
566 * cap_bprm_secureexec - Determine whether a secure execution is required
567 * @bprm: The execution parameters
568 *
569 * Determine whether a secure execution is required, return 1 if it is, and 0
570 * if it is not.
571 *
572 * The credentials have been committed by this point, and so are no longer
573 * available through @bprm->cred.
574 */
cap_bprm_secureexec(struct linux_binprm * bprm)575 int cap_bprm_secureexec(struct linux_binprm *bprm)
576 {
577 const struct cred *cred = current_cred();
578
579 if (cred->uid != 0) {
580 if (bprm->cap_effective)
581 return 1;
582 if (!cap_isclear(cred->cap_permitted))
583 return 1;
584 }
585
586 return (cred->euid != cred->uid ||
587 cred->egid != cred->gid);
588 }
589
590 /**
591 * cap_inode_setxattr - Determine whether an xattr may be altered
592 * @dentry: The inode/dentry being altered
593 * @name: The name of the xattr to be changed
594 * @value: The value that the xattr will be changed to
595 * @size: The size of value
596 * @flags: The replacement flag
597 *
598 * Determine whether an xattr may be altered or set on an inode, returning 0 if
599 * permission is granted, -ve if denied.
600 *
601 * This is used to make sure security xattrs don't get updated or set by those
602 * who aren't privileged to do so.
603 */
cap_inode_setxattr(struct dentry * dentry,const char * name,const void * value,size_t size,int flags)604 int cap_inode_setxattr(struct dentry *dentry, const char *name,
605 const void *value, size_t size, int flags)
606 {
607 if (!strcmp(name, XATTR_NAME_CAPS)) {
608 if (!capable(CAP_SETFCAP))
609 return -EPERM;
610 return 0;
611 }
612
613 if (!strncmp(name, XATTR_SECURITY_PREFIX,
614 sizeof(XATTR_SECURITY_PREFIX) - 1) &&
615 !capable(CAP_SYS_ADMIN))
616 return -EPERM;
617 return 0;
618 }
619
620 /**
621 * cap_inode_removexattr - Determine whether an xattr may be removed
622 * @dentry: The inode/dentry being altered
623 * @name: The name of the xattr to be changed
624 *
625 * Determine whether an xattr may be removed from an inode, returning 0 if
626 * permission is granted, -ve if denied.
627 *
628 * This is used to make sure security xattrs don't get removed by those who
629 * aren't privileged to remove them.
630 */
cap_inode_removexattr(struct dentry * dentry,const char * name)631 int cap_inode_removexattr(struct dentry *dentry, const char *name)
632 {
633 if (!strcmp(name, XATTR_NAME_CAPS)) {
634 if (!capable(CAP_SETFCAP))
635 return -EPERM;
636 return 0;
637 }
638
639 if (!strncmp(name, XATTR_SECURITY_PREFIX,
640 sizeof(XATTR_SECURITY_PREFIX) - 1) &&
641 !capable(CAP_SYS_ADMIN))
642 return -EPERM;
643 return 0;
644 }
645
646 /*
647 * cap_emulate_setxuid() fixes the effective / permitted capabilities of
648 * a process after a call to setuid, setreuid, or setresuid.
649 *
650 * 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
651 * {r,e,s}uid != 0, the permitted and effective capabilities are
652 * cleared.
653 *
654 * 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
655 * capabilities of the process are cleared.
656 *
657 * 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
658 * capabilities are set to the permitted capabilities.
659 *
660 * fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
661 * never happen.
662 *
663 * -astor
664 *
665 * cevans - New behaviour, Oct '99
666 * A process may, via prctl(), elect to keep its capabilities when it
667 * calls setuid() and switches away from uid==0. Both permitted and
668 * effective sets will be retained.
669 * Without this change, it was impossible for a daemon to drop only some
670 * of its privilege. The call to setuid(!=0) would drop all privileges!
671 * Keeping uid 0 is not an option because uid 0 owns too many vital
672 * files..
673 * Thanks to Olaf Kirch and Peter Benie for spotting this.
674 */
cap_emulate_setxuid(struct cred * new,const struct cred * old)675 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
676 {
677 if ((old->uid == 0 || old->euid == 0 || old->suid == 0) &&
678 (new->uid != 0 && new->euid != 0 && new->suid != 0) &&
679 !issecure(SECURE_KEEP_CAPS)) {
680 cap_clear(new->cap_permitted);
681 cap_clear(new->cap_effective);
682 }
683 if (old->euid == 0 && new->euid != 0)
684 cap_clear(new->cap_effective);
685 if (old->euid != 0 && new->euid == 0)
686 new->cap_effective = new->cap_permitted;
687 }
688
689 /**
690 * cap_task_fix_setuid - Fix up the results of setuid() call
691 * @new: The proposed credentials
692 * @old: The current task's current credentials
693 * @flags: Indications of what has changed
694 *
695 * Fix up the results of setuid() call before the credential changes are
696 * actually applied, returning 0 to grant the changes, -ve to deny them.
697 */
cap_task_fix_setuid(struct cred * new,const struct cred * old,int flags)698 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
699 {
700 switch (flags) {
701 case LSM_SETID_RE:
702 case LSM_SETID_ID:
703 case LSM_SETID_RES:
704 /* juggle the capabilities to follow [RES]UID changes unless
705 * otherwise suppressed */
706 if (!issecure(SECURE_NO_SETUID_FIXUP))
707 cap_emulate_setxuid(new, old);
708 break;
709
710 case LSM_SETID_FS:
711 /* juggle the capabilties to follow FSUID changes, unless
712 * otherwise suppressed
713 *
714 * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
715 * if not, we might be a bit too harsh here.
716 */
717 if (!issecure(SECURE_NO_SETUID_FIXUP)) {
718 if (old->fsuid == 0 && new->fsuid != 0)
719 new->cap_effective =
720 cap_drop_fs_set(new->cap_effective);
721
722 if (old->fsuid != 0 && new->fsuid == 0)
723 new->cap_effective =
724 cap_raise_fs_set(new->cap_effective,
725 new->cap_permitted);
726 }
727 break;
728
729 default:
730 return -EINVAL;
731 }
732
733 return 0;
734 }
735
736 /*
737 * Rationale: code calling task_setscheduler, task_setioprio, and
738 * task_setnice, assumes that
739 * . if capable(cap_sys_nice), then those actions should be allowed
740 * . if not capable(cap_sys_nice), but acting on your own processes,
741 * then those actions should be allowed
742 * This is insufficient now since you can call code without suid, but
743 * yet with increased caps.
744 * So we check for increased caps on the target process.
745 */
cap_safe_nice(struct task_struct * p)746 static int cap_safe_nice(struct task_struct *p)
747 {
748 int is_subset;
749
750 rcu_read_lock();
751 is_subset = cap_issubset(__task_cred(p)->cap_permitted,
752 current_cred()->cap_permitted);
753 rcu_read_unlock();
754
755 if (!is_subset && !capable(CAP_SYS_NICE))
756 return -EPERM;
757 return 0;
758 }
759
760 /**
761 * cap_task_setscheduler - Detemine if scheduler policy change is permitted
762 * @p: The task to affect
763 *
764 * Detemine if the requested scheduler policy change is permitted for the
765 * specified task, returning 0 if permission is granted, -ve if denied.
766 */
cap_task_setscheduler(struct task_struct * p)767 int cap_task_setscheduler(struct task_struct *p)
768 {
769 return cap_safe_nice(p);
770 }
771
772 /**
773 * cap_task_ioprio - Detemine if I/O priority change is permitted
774 * @p: The task to affect
775 * @ioprio: The I/O priority to set
776 *
777 * Detemine if the requested I/O priority change is permitted for the specified
778 * task, returning 0 if permission is granted, -ve if denied.
779 */
cap_task_setioprio(struct task_struct * p,int ioprio)780 int cap_task_setioprio(struct task_struct *p, int ioprio)
781 {
782 return cap_safe_nice(p);
783 }
784
785 /**
786 * cap_task_ioprio - Detemine if task priority change is permitted
787 * @p: The task to affect
788 * @nice: The nice value to set
789 *
790 * Detemine if the requested task priority change is permitted for the
791 * specified task, returning 0 if permission is granted, -ve if denied.
792 */
cap_task_setnice(struct task_struct * p,int nice)793 int cap_task_setnice(struct task_struct *p, int nice)
794 {
795 return cap_safe_nice(p);
796 }
797
798 /*
799 * Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from
800 * the current task's bounding set. Returns 0 on success, -ve on error.
801 */
cap_prctl_drop(struct cred * new,unsigned long cap)802 static long cap_prctl_drop(struct cred *new, unsigned long cap)
803 {
804 if (!capable(CAP_SETPCAP))
805 return -EPERM;
806 if (!cap_valid(cap))
807 return -EINVAL;
808
809 cap_lower(new->cap_bset, cap);
810 return 0;
811 }
812
813 /**
814 * cap_task_prctl - Implement process control functions for this security module
815 * @option: The process control function requested
816 * @arg2, @arg3, @arg4, @arg5: The argument data for this function
817 *
818 * Allow process control functions (sys_prctl()) to alter capabilities; may
819 * also deny access to other functions not otherwise implemented here.
820 *
821 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented
822 * here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM
823 * modules will consider performing the function.
824 */
cap_task_prctl(int option,unsigned long arg2,unsigned long arg3,unsigned long arg4,unsigned long arg5)825 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
826 unsigned long arg4, unsigned long arg5)
827 {
828 struct cred *new;
829 long error = 0;
830
831 new = prepare_creds();
832 if (!new)
833 return -ENOMEM;
834
835 switch (option) {
836 case PR_CAPBSET_READ:
837 error = -EINVAL;
838 if (!cap_valid(arg2))
839 goto error;
840 error = !!cap_raised(new->cap_bset, arg2);
841 goto no_change;
842
843 case PR_CAPBSET_DROP:
844 error = cap_prctl_drop(new, arg2);
845 if (error < 0)
846 goto error;
847 goto changed;
848
849 /*
850 * The next four prctl's remain to assist with transitioning a
851 * system from legacy UID=0 based privilege (when filesystem
852 * capabilities are not in use) to a system using filesystem
853 * capabilities only - as the POSIX.1e draft intended.
854 *
855 * Note:
856 *
857 * PR_SET_SECUREBITS =
858 * issecure_mask(SECURE_KEEP_CAPS_LOCKED)
859 * | issecure_mask(SECURE_NOROOT)
860 * | issecure_mask(SECURE_NOROOT_LOCKED)
861 * | issecure_mask(SECURE_NO_SETUID_FIXUP)
862 * | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
863 *
864 * will ensure that the current process and all of its
865 * children will be locked into a pure
866 * capability-based-privilege environment.
867 */
868 case PR_SET_SECUREBITS:
869 error = -EPERM;
870 if ((((new->securebits & SECURE_ALL_LOCKS) >> 1)
871 & (new->securebits ^ arg2)) /*[1]*/
872 || ((new->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
873 || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
874 || (cap_capable(current_cred(),
875 current_cred()->user->user_ns, CAP_SETPCAP,
876 SECURITY_CAP_AUDIT) != 0) /*[4]*/
877 /*
878 * [1] no changing of bits that are locked
879 * [2] no unlocking of locks
880 * [3] no setting of unsupported bits
881 * [4] doing anything requires privilege (go read about
882 * the "sendmail capabilities bug")
883 */
884 )
885 /* cannot change a locked bit */
886 goto error;
887 new->securebits = arg2;
888 goto changed;
889
890 case PR_GET_SECUREBITS:
891 error = new->securebits;
892 goto no_change;
893
894 case PR_GET_KEEPCAPS:
895 if (issecure(SECURE_KEEP_CAPS))
896 error = 1;
897 goto no_change;
898
899 case PR_SET_KEEPCAPS:
900 error = -EINVAL;
901 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
902 goto error;
903 error = -EPERM;
904 if (issecure(SECURE_KEEP_CAPS_LOCKED))
905 goto error;
906 if (arg2)
907 new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
908 else
909 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
910 goto changed;
911
912 default:
913 /* No functionality available - continue with default */
914 error = -ENOSYS;
915 goto error;
916 }
917
918 /* Functionality provided */
919 changed:
920 return commit_creds(new);
921
922 no_change:
923 error:
924 abort_creds(new);
925 return error;
926 }
927
928 /**
929 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
930 * @mm: The VM space in which the new mapping is to be made
931 * @pages: The size of the mapping
932 *
933 * Determine whether the allocation of a new virtual mapping by the current
934 * task is permitted, returning 0 if permission is granted, -ve if not.
935 */
cap_vm_enough_memory(struct mm_struct * mm,long pages)936 int cap_vm_enough_memory(struct mm_struct *mm, long pages)
937 {
938 int cap_sys_admin = 0;
939
940 if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
941 SECURITY_CAP_NOAUDIT) == 0)
942 cap_sys_admin = 1;
943 return __vm_enough_memory(mm, pages, cap_sys_admin);
944 }
945
946 /*
947 * cap_file_mmap - check if able to map given addr
948 * @file: unused
949 * @reqprot: unused
950 * @prot: unused
951 * @flags: unused
952 * @addr: address attempting to be mapped
953 * @addr_only: unused
954 *
955 * If the process is attempting to map memory below dac_mmap_min_addr they need
956 * CAP_SYS_RAWIO. The other parameters to this function are unused by the
957 * capability security module. Returns 0 if this mapping should be allowed
958 * -EPERM if not.
959 */
cap_file_mmap(struct file * file,unsigned long reqprot,unsigned long prot,unsigned long flags,unsigned long addr,unsigned long addr_only)960 int cap_file_mmap(struct file *file, unsigned long reqprot,
961 unsigned long prot, unsigned long flags,
962 unsigned long addr, unsigned long addr_only)
963 {
964 int ret = 0;
965
966 if (addr < dac_mmap_min_addr) {
967 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
968 SECURITY_CAP_AUDIT);
969 /* set PF_SUPERPRIV if it turns out we allow the low mmap */
970 if (ret == 0)
971 current->flags |= PF_SUPERPRIV;
972 }
973 return ret;
974 }
975