1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Common capabilities, needed by capability.o.
3 */
4
5 #include <linux/capability.h>
6 #include <linux/audit.h>
7 #include <linux/init.h>
8 #include <linux/kernel.h>
9 #include <linux/lsm_hooks.h>
10 #include <linux/file.h>
11 #include <linux/mm.h>
12 #include <linux/mman.h>
13 #include <linux/pagemap.h>
14 #include <linux/swap.h>
15 #include <linux/skbuff.h>
16 #include <linux/netlink.h>
17 #include <linux/ptrace.h>
18 #include <linux/xattr.h>
19 #include <linux/hugetlb.h>
20 #include <linux/mount.h>
21 #include <linux/sched.h>
22 #include <linux/prctl.h>
23 #include <linux/securebits.h>
24 #include <linux/user_namespace.h>
25 #include <linux/binfmts.h>
26 #include <linux/personality.h>
27 #include <linux/mnt_idmapping.h>
28
29 /*
30 * If a non-root user executes a setuid-root binary in
31 * !secure(SECURE_NOROOT) mode, then we raise capabilities.
32 * However if fE is also set, then the intent is for only
33 * the file capabilities to be applied, and the setuid-root
34 * bit is left on either to change the uid (plausible) or
35 * to get full privilege on a kernel without file capabilities
36 * support. So in that case we do not raise capabilities.
37 *
38 * Warn if that happens, once per boot.
39 */
warn_setuid_and_fcaps_mixed(const char * fname)40 static void warn_setuid_and_fcaps_mixed(const char *fname)
41 {
42 static int warned;
43 if (!warned) {
44 printk(KERN_INFO "warning: `%s' has both setuid-root and"
45 " effective capabilities. Therefore not raising all"
46 " capabilities.\n", fname);
47 warned = 1;
48 }
49 }
50
51 /**
52 * cap_capable - Determine whether a task has a particular effective capability
53 * @cred: The credentials to use
54 * @targ_ns: The user namespace in which we need the capability
55 * @cap: The capability to check for
56 * @opts: Bitmask of options defined in include/linux/security.h
57 *
58 * Determine whether the nominated task has the specified capability amongst
59 * its effective set, returning 0 if it does, -ve if it does not.
60 *
61 * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
62 * and has_capability() functions. That is, it has the reverse semantics:
63 * cap_has_capability() returns 0 when a task has a capability, but the
64 * kernel's capable() and has_capability() returns 1 for this case.
65 */
cap_capable(const struct cred * cred,struct user_namespace * targ_ns,int cap,unsigned int opts)66 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
67 int cap, unsigned int opts)
68 {
69 struct user_namespace *ns = targ_ns;
70
71 /* See if cred has the capability in the target user namespace
72 * by examining the target user namespace and all of the target
73 * user namespace's parents.
74 */
75 for (;;) {
76 /* Do we have the necessary capabilities? */
77 if (ns == cred->user_ns)
78 return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
79
80 /*
81 * If we're already at a lower level than we're looking for,
82 * we're done searching.
83 */
84 if (ns->level <= cred->user_ns->level)
85 return -EPERM;
86
87 /*
88 * The owner of the user namespace in the parent of the
89 * user namespace has all caps.
90 */
91 if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
92 return 0;
93
94 /*
95 * If you have a capability in a parent user ns, then you have
96 * it over all children user namespaces as well.
97 */
98 ns = ns->parent;
99 }
100
101 /* We never get here */
102 }
103
104 /**
105 * cap_settime - Determine whether the current process may set the system clock
106 * @ts: The time to set
107 * @tz: The timezone to set
108 *
109 * Determine whether the current process may set the system clock and timezone
110 * information, returning 0 if permission granted, -ve if denied.
111 */
cap_settime(const struct timespec64 * ts,const struct timezone * tz)112 int cap_settime(const struct timespec64 *ts, const struct timezone *tz)
113 {
114 if (!capable(CAP_SYS_TIME))
115 return -EPERM;
116 return 0;
117 }
118
119 /**
120 * cap_ptrace_access_check - Determine whether the current process may access
121 * another
122 * @child: The process to be accessed
123 * @mode: The mode of attachment.
124 *
125 * If we are in the same or an ancestor user_ns and have all the target
126 * task's capabilities, then ptrace access is allowed.
127 * If we have the ptrace capability to the target user_ns, then ptrace
128 * access is allowed.
129 * Else denied.
130 *
131 * Determine whether a process may access another, returning 0 if permission
132 * granted, -ve if denied.
133 */
cap_ptrace_access_check(struct task_struct * child,unsigned int mode)134 int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
135 {
136 int ret = 0;
137 const struct cred *cred, *child_cred;
138 const kernel_cap_t *caller_caps;
139
140 rcu_read_lock();
141 cred = current_cred();
142 child_cred = __task_cred(child);
143 if (mode & PTRACE_MODE_FSCREDS)
144 caller_caps = &cred->cap_effective;
145 else
146 caller_caps = &cred->cap_permitted;
147 if (cred->user_ns == child_cred->user_ns &&
148 cap_issubset(child_cred->cap_permitted, *caller_caps))
149 goto out;
150 if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
151 goto out;
152 ret = -EPERM;
153 out:
154 rcu_read_unlock();
155 return ret;
156 }
157
158 /**
159 * cap_ptrace_traceme - Determine whether another process may trace the current
160 * @parent: The task proposed to be the tracer
161 *
162 * If parent is in the same or an ancestor user_ns and has all current's
163 * capabilities, then ptrace access is allowed.
164 * If parent has the ptrace capability to current's user_ns, then ptrace
165 * access is allowed.
166 * Else denied.
167 *
168 * Determine whether the nominated task is permitted to trace the current
169 * process, returning 0 if permission is granted, -ve if denied.
170 */
cap_ptrace_traceme(struct task_struct * parent)171 int cap_ptrace_traceme(struct task_struct *parent)
172 {
173 int ret = 0;
174 const struct cred *cred, *child_cred;
175
176 rcu_read_lock();
177 cred = __task_cred(parent);
178 child_cred = current_cred();
179 if (cred->user_ns == child_cred->user_ns &&
180 cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
181 goto out;
182 if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE))
183 goto out;
184 ret = -EPERM;
185 out:
186 rcu_read_unlock();
187 return ret;
188 }
189
190 /**
191 * cap_capget - Retrieve a task's capability sets
192 * @target: The task from which to retrieve the capability sets
193 * @effective: The place to record the effective set
194 * @inheritable: The place to record the inheritable set
195 * @permitted: The place to record the permitted set
196 *
197 * This function retrieves the capabilities of the nominated task and returns
198 * them to the caller.
199 */
cap_capget(struct task_struct * target,kernel_cap_t * effective,kernel_cap_t * inheritable,kernel_cap_t * permitted)200 int cap_capget(struct task_struct *target, kernel_cap_t *effective,
201 kernel_cap_t *inheritable, kernel_cap_t *permitted)
202 {
203 const struct cred *cred;
204
205 /* Derived from kernel/capability.c:sys_capget. */
206 rcu_read_lock();
207 cred = __task_cred(target);
208 *effective = cred->cap_effective;
209 *inheritable = cred->cap_inheritable;
210 *permitted = cred->cap_permitted;
211 rcu_read_unlock();
212 return 0;
213 }
214
215 /*
216 * Determine whether the inheritable capabilities are limited to the old
217 * permitted set. Returns 1 if they are limited, 0 if they are not.
218 */
cap_inh_is_capped(void)219 static inline int cap_inh_is_capped(void)
220 {
221 /* they are so limited unless the current task has the CAP_SETPCAP
222 * capability
223 */
224 if (cap_capable(current_cred(), current_cred()->user_ns,
225 CAP_SETPCAP, CAP_OPT_NONE) == 0)
226 return 0;
227 return 1;
228 }
229
230 /**
231 * cap_capset - Validate and apply proposed changes to current's capabilities
232 * @new: The proposed new credentials; alterations should be made here
233 * @old: The current task's current credentials
234 * @effective: A pointer to the proposed new effective capabilities set
235 * @inheritable: A pointer to the proposed new inheritable capabilities set
236 * @permitted: A pointer to the proposed new permitted capabilities set
237 *
238 * This function validates and applies a proposed mass change to the current
239 * process's capability sets. The changes are made to the proposed new
240 * credentials, and assuming no error, will be committed by the caller of LSM.
241 */
cap_capset(struct cred * new,const struct cred * old,const kernel_cap_t * effective,const kernel_cap_t * inheritable,const kernel_cap_t * permitted)242 int cap_capset(struct cred *new,
243 const struct cred *old,
244 const kernel_cap_t *effective,
245 const kernel_cap_t *inheritable,
246 const kernel_cap_t *permitted)
247 {
248 if (cap_inh_is_capped() &&
249 !cap_issubset(*inheritable,
250 cap_combine(old->cap_inheritable,
251 old->cap_permitted)))
252 /* incapable of using this inheritable set */
253 return -EPERM;
254
255 if (!cap_issubset(*inheritable,
256 cap_combine(old->cap_inheritable,
257 old->cap_bset)))
258 /* no new pI capabilities outside bounding set */
259 return -EPERM;
260
261 /* verify restrictions on target's new Permitted set */
262 if (!cap_issubset(*permitted, old->cap_permitted))
263 return -EPERM;
264
265 /* verify the _new_Effective_ is a subset of the _new_Permitted_ */
266 if (!cap_issubset(*effective, *permitted))
267 return -EPERM;
268
269 new->cap_effective = *effective;
270 new->cap_inheritable = *inheritable;
271 new->cap_permitted = *permitted;
272
273 /*
274 * Mask off ambient bits that are no longer both permitted and
275 * inheritable.
276 */
277 new->cap_ambient = cap_intersect(new->cap_ambient,
278 cap_intersect(*permitted,
279 *inheritable));
280 if (WARN_ON(!cap_ambient_invariant_ok(new)))
281 return -EINVAL;
282 return 0;
283 }
284
285 /**
286 * cap_inode_need_killpriv - Determine if inode change affects privileges
287 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
288 *
289 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
290 * affects the security markings on that inode, and if it is, should
291 * inode_killpriv() be invoked or the change rejected.
292 *
293 * Return: 1 if security.capability has a value, meaning inode_killpriv()
294 * is required, 0 otherwise, meaning inode_killpriv() is not required.
295 */
cap_inode_need_killpriv(struct dentry * dentry)296 int cap_inode_need_killpriv(struct dentry *dentry)
297 {
298 struct inode *inode = d_backing_inode(dentry);
299 int error;
300
301 error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
302 return error > 0;
303 }
304
305 /**
306 * cap_inode_killpriv - Erase the security markings on an inode
307 *
308 * @mnt_userns: user namespace of the mount the inode was found from
309 * @dentry: The inode/dentry to alter
310 *
311 * Erase the privilege-enhancing security markings on an inode.
312 *
313 * If the inode has been found through an idmapped mount the user namespace of
314 * the vfsmount must be passed through @mnt_userns. This function will then
315 * take care to map the inode according to @mnt_userns before checking
316 * permissions. On non-idmapped mounts or if permission checking is to be
317 * performed on the raw inode simply passs init_user_ns.
318 *
319 * Return: 0 if successful, -ve on error.
320 */
cap_inode_killpriv(struct user_namespace * mnt_userns,struct dentry * dentry)321 int cap_inode_killpriv(struct user_namespace *mnt_userns, struct dentry *dentry)
322 {
323 int error;
324
325 error = __vfs_removexattr(mnt_userns, dentry, XATTR_NAME_CAPS);
326 if (error == -EOPNOTSUPP)
327 error = 0;
328 return error;
329 }
330
rootid_owns_currentns(kuid_t kroot)331 static bool rootid_owns_currentns(kuid_t kroot)
332 {
333 struct user_namespace *ns;
334
335 if (!uid_valid(kroot))
336 return false;
337
338 for (ns = current_user_ns(); ; ns = ns->parent) {
339 if (from_kuid(ns, kroot) == 0)
340 return true;
341 if (ns == &init_user_ns)
342 break;
343 }
344
345 return false;
346 }
347
sansflags(__u32 m)348 static __u32 sansflags(__u32 m)
349 {
350 return m & ~VFS_CAP_FLAGS_EFFECTIVE;
351 }
352
is_v2header(size_t size,const struct vfs_cap_data * cap)353 static bool is_v2header(size_t size, const struct vfs_cap_data *cap)
354 {
355 if (size != XATTR_CAPS_SZ_2)
356 return false;
357 return sansflags(le32_to_cpu(cap->magic_etc)) == VFS_CAP_REVISION_2;
358 }
359
is_v3header(size_t size,const struct vfs_cap_data * cap)360 static bool is_v3header(size_t size, const struct vfs_cap_data *cap)
361 {
362 if (size != XATTR_CAPS_SZ_3)
363 return false;
364 return sansflags(le32_to_cpu(cap->magic_etc)) == VFS_CAP_REVISION_3;
365 }
366
367 /*
368 * getsecurity: We are called for security.* before any attempt to read the
369 * xattr from the inode itself.
370 *
371 * This gives us a chance to read the on-disk value and convert it. If we
372 * return -EOPNOTSUPP, then vfs_getxattr() will call the i_op handler.
373 *
374 * Note we are not called by vfs_getxattr_alloc(), but that is only called
375 * by the integrity subsystem, which really wants the unconverted values -
376 * so that's good.
377 */
cap_inode_getsecurity(struct user_namespace * mnt_userns,struct inode * inode,const char * name,void ** buffer,bool alloc)378 int cap_inode_getsecurity(struct user_namespace *mnt_userns,
379 struct inode *inode, const char *name, void **buffer,
380 bool alloc)
381 {
382 int size, ret;
383 kuid_t kroot;
384 u32 nsmagic, magic;
385 uid_t root, mappedroot;
386 char *tmpbuf = NULL;
387 struct vfs_cap_data *cap;
388 struct vfs_ns_cap_data *nscap = NULL;
389 struct dentry *dentry;
390 struct user_namespace *fs_ns;
391
392 if (strcmp(name, "capability") != 0)
393 return -EOPNOTSUPP;
394
395 dentry = d_find_any_alias(inode);
396 if (!dentry)
397 return -EINVAL;
398
399 size = sizeof(struct vfs_ns_cap_data);
400 ret = (int)vfs_getxattr_alloc(mnt_userns, dentry, XATTR_NAME_CAPS,
401 &tmpbuf, size, GFP_NOFS);
402 dput(dentry);
403
404 if (ret < 0 || !tmpbuf) {
405 size = ret;
406 goto out_free;
407 }
408
409 fs_ns = inode->i_sb->s_user_ns;
410 cap = (struct vfs_cap_data *) tmpbuf;
411 if (is_v2header((size_t) ret, cap)) {
412 root = 0;
413 } else if (is_v3header((size_t) ret, cap)) {
414 nscap = (struct vfs_ns_cap_data *) tmpbuf;
415 root = le32_to_cpu(nscap->rootid);
416 } else {
417 size = -EINVAL;
418 goto out_free;
419 }
420
421 kroot = make_kuid(fs_ns, root);
422
423 /* If this is an idmapped mount shift the kuid. */
424 kroot = mapped_kuid_fs(mnt_userns, fs_ns, kroot);
425
426 /* If the root kuid maps to a valid uid in current ns, then return
427 * this as a nscap. */
428 mappedroot = from_kuid(current_user_ns(), kroot);
429 if (mappedroot != (uid_t)-1 && mappedroot != (uid_t)0) {
430 size = sizeof(struct vfs_ns_cap_data);
431 if (alloc) {
432 if (!nscap) {
433 /* v2 -> v3 conversion */
434 nscap = kzalloc(size, GFP_ATOMIC);
435 if (!nscap) {
436 size = -ENOMEM;
437 goto out_free;
438 }
439 nsmagic = VFS_CAP_REVISION_3;
440 magic = le32_to_cpu(cap->magic_etc);
441 if (magic & VFS_CAP_FLAGS_EFFECTIVE)
442 nsmagic |= VFS_CAP_FLAGS_EFFECTIVE;
443 memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
444 nscap->magic_etc = cpu_to_le32(nsmagic);
445 } else {
446 /* use allocated v3 buffer */
447 tmpbuf = NULL;
448 }
449 nscap->rootid = cpu_to_le32(mappedroot);
450 *buffer = nscap;
451 }
452 goto out_free;
453 }
454
455 if (!rootid_owns_currentns(kroot)) {
456 size = -EOVERFLOW;
457 goto out_free;
458 }
459
460 /* This comes from a parent namespace. Return as a v2 capability */
461 size = sizeof(struct vfs_cap_data);
462 if (alloc) {
463 if (nscap) {
464 /* v3 -> v2 conversion */
465 cap = kzalloc(size, GFP_ATOMIC);
466 if (!cap) {
467 size = -ENOMEM;
468 goto out_free;
469 }
470 magic = VFS_CAP_REVISION_2;
471 nsmagic = le32_to_cpu(nscap->magic_etc);
472 if (nsmagic & VFS_CAP_FLAGS_EFFECTIVE)
473 magic |= VFS_CAP_FLAGS_EFFECTIVE;
474 memcpy(&cap->data, &nscap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
475 cap->magic_etc = cpu_to_le32(magic);
476 } else {
477 /* use unconverted v2 */
478 tmpbuf = NULL;
479 }
480 *buffer = cap;
481 }
482 out_free:
483 kfree(tmpbuf);
484 return size;
485 }
486
487 /**
488 * rootid_from_xattr - translate root uid of vfs caps
489 *
490 * @value: vfs caps value which may be modified by this function
491 * @size: size of @ivalue
492 * @task_ns: user namespace of the caller
493 * @mnt_userns: user namespace of the mount the inode was found from
494 * @fs_userns: user namespace of the filesystem
495 *
496 * If the inode has been found through an idmapped mount the user namespace of
497 * the vfsmount must be passed through @mnt_userns. This function will then
498 * take care to map the inode according to @mnt_userns before checking
499 * permissions. On non-idmapped mounts or if permission checking is to be
500 * performed on the raw inode simply passs init_user_ns.
501 */
rootid_from_xattr(const void * value,size_t size,struct user_namespace * task_ns,struct user_namespace * mnt_userns,struct user_namespace * fs_userns)502 static kuid_t rootid_from_xattr(const void *value, size_t size,
503 struct user_namespace *task_ns,
504 struct user_namespace *mnt_userns,
505 struct user_namespace *fs_userns)
506 {
507 const struct vfs_ns_cap_data *nscap = value;
508 kuid_t rootkid;
509 uid_t rootid = 0;
510
511 if (size == XATTR_CAPS_SZ_3)
512 rootid = le32_to_cpu(nscap->rootid);
513
514 rootkid = make_kuid(task_ns, rootid);
515 return mapped_kuid_user(mnt_userns, fs_userns, rootkid);
516 }
517
validheader(size_t size,const struct vfs_cap_data * cap)518 static bool validheader(size_t size, const struct vfs_cap_data *cap)
519 {
520 return is_v2header(size, cap) || is_v3header(size, cap);
521 }
522
523 /**
524 * cap_convert_nscap - check vfs caps
525 *
526 * @mnt_userns: user namespace of the mount the inode was found from
527 * @dentry: used to retrieve inode to check permissions on
528 * @ivalue: vfs caps value which may be modified by this function
529 * @size: size of @ivalue
530 *
531 * User requested a write of security.capability. If needed, update the
532 * xattr to change from v2 to v3, or to fixup the v3 rootid.
533 *
534 * If the inode has been found through an idmapped mount the user namespace of
535 * the vfsmount must be passed through @mnt_userns. This function will then
536 * take care to map the inode according to @mnt_userns before checking
537 * permissions. On non-idmapped mounts or if permission checking is to be
538 * performed on the raw inode simply passs init_user_ns.
539 *
540 * Return: On success, return the new size; on error, return < 0.
541 */
cap_convert_nscap(struct user_namespace * mnt_userns,struct dentry * dentry,const void ** ivalue,size_t size)542 int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
543 const void **ivalue, size_t size)
544 {
545 struct vfs_ns_cap_data *nscap;
546 uid_t nsrootid;
547 const struct vfs_cap_data *cap = *ivalue;
548 __u32 magic, nsmagic;
549 struct inode *inode = d_backing_inode(dentry);
550 struct user_namespace *task_ns = current_user_ns(),
551 *fs_ns = inode->i_sb->s_user_ns;
552 kuid_t rootid;
553 size_t newsize;
554
555 if (!*ivalue)
556 return -EINVAL;
557 if (!validheader(size, cap))
558 return -EINVAL;
559 if (!capable_wrt_inode_uidgid(mnt_userns, inode, CAP_SETFCAP))
560 return -EPERM;
561 if (size == XATTR_CAPS_SZ_2 && (mnt_userns == fs_ns))
562 if (ns_capable(inode->i_sb->s_user_ns, CAP_SETFCAP))
563 /* user is privileged, just write the v2 */
564 return size;
565
566 rootid = rootid_from_xattr(*ivalue, size, task_ns, mnt_userns, fs_ns);
567 if (!uid_valid(rootid))
568 return -EINVAL;
569
570 nsrootid = from_kuid(fs_ns, rootid);
571 if (nsrootid == -1)
572 return -EINVAL;
573
574 newsize = sizeof(struct vfs_ns_cap_data);
575 nscap = kmalloc(newsize, GFP_ATOMIC);
576 if (!nscap)
577 return -ENOMEM;
578 nscap->rootid = cpu_to_le32(nsrootid);
579 nsmagic = VFS_CAP_REVISION_3;
580 magic = le32_to_cpu(cap->magic_etc);
581 if (magic & VFS_CAP_FLAGS_EFFECTIVE)
582 nsmagic |= VFS_CAP_FLAGS_EFFECTIVE;
583 nscap->magic_etc = cpu_to_le32(nsmagic);
584 memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
585
586 *ivalue = nscap;
587 return newsize;
588 }
589
590 /*
591 * Calculate the new process capability sets from the capability sets attached
592 * to a file.
593 */
bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data * caps,struct linux_binprm * bprm,bool * effective,bool * has_fcap)594 static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
595 struct linux_binprm *bprm,
596 bool *effective,
597 bool *has_fcap)
598 {
599 struct cred *new = bprm->cred;
600 unsigned i;
601 int ret = 0;
602
603 if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
604 *effective = true;
605
606 if (caps->magic_etc & VFS_CAP_REVISION_MASK)
607 *has_fcap = true;
608
609 CAP_FOR_EACH_U32(i) {
610 __u32 permitted = caps->permitted.cap[i];
611 __u32 inheritable = caps->inheritable.cap[i];
612
613 /*
614 * pP' = (X & fP) | (pI & fI)
615 * The addition of pA' is handled later.
616 */
617 new->cap_permitted.cap[i] =
618 (new->cap_bset.cap[i] & permitted) |
619 (new->cap_inheritable.cap[i] & inheritable);
620
621 if (permitted & ~new->cap_permitted.cap[i])
622 /* insufficient to execute correctly */
623 ret = -EPERM;
624 }
625
626 /*
627 * For legacy apps, with no internal support for recognizing they
628 * do not have enough capabilities, we return an error if they are
629 * missing some "forced" (aka file-permitted) capabilities.
630 */
631 return *effective ? ret : 0;
632 }
633
634 /**
635 * get_vfs_caps_from_disk - retrieve vfs caps from disk
636 *
637 * @mnt_userns: user namespace of the mount the inode was found from
638 * @dentry: dentry from which @inode is retrieved
639 * @cpu_caps: vfs capabilities
640 *
641 * Extract the on-exec-apply capability sets for an executable file.
642 *
643 * If the inode has been found through an idmapped mount the user namespace of
644 * the vfsmount must be passed through @mnt_userns. This function will then
645 * take care to map the inode according to @mnt_userns before checking
646 * permissions. On non-idmapped mounts or if permission checking is to be
647 * performed on the raw inode simply passs init_user_ns.
648 */
get_vfs_caps_from_disk(struct user_namespace * mnt_userns,const struct dentry * dentry,struct cpu_vfs_cap_data * cpu_caps)649 int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
650 const struct dentry *dentry,
651 struct cpu_vfs_cap_data *cpu_caps)
652 {
653 struct inode *inode = d_backing_inode(dentry);
654 __u32 magic_etc;
655 unsigned tocopy, i;
656 int size;
657 struct vfs_ns_cap_data data, *nscaps = &data;
658 struct vfs_cap_data *caps = (struct vfs_cap_data *) &data;
659 kuid_t rootkuid;
660 struct user_namespace *fs_ns;
661
662 memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
663
664 if (!inode)
665 return -ENODATA;
666
667 fs_ns = inode->i_sb->s_user_ns;
668 size = __vfs_getxattr((struct dentry *)dentry, inode,
669 XATTR_NAME_CAPS, &data, XATTR_CAPS_SZ);
670 if (size == -ENODATA || size == -EOPNOTSUPP)
671 /* no data, that's ok */
672 return -ENODATA;
673
674 if (size < 0)
675 return size;
676
677 if (size < sizeof(magic_etc))
678 return -EINVAL;
679
680 cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps->magic_etc);
681
682 rootkuid = make_kuid(fs_ns, 0);
683 switch (magic_etc & VFS_CAP_REVISION_MASK) {
684 case VFS_CAP_REVISION_1:
685 if (size != XATTR_CAPS_SZ_1)
686 return -EINVAL;
687 tocopy = VFS_CAP_U32_1;
688 break;
689 case VFS_CAP_REVISION_2:
690 if (size != XATTR_CAPS_SZ_2)
691 return -EINVAL;
692 tocopy = VFS_CAP_U32_2;
693 break;
694 case VFS_CAP_REVISION_3:
695 if (size != XATTR_CAPS_SZ_3)
696 return -EINVAL;
697 tocopy = VFS_CAP_U32_3;
698 rootkuid = make_kuid(fs_ns, le32_to_cpu(nscaps->rootid));
699 break;
700
701 default:
702 return -EINVAL;
703 }
704 /* Limit the caps to the mounter of the filesystem
705 * or the more limited uid specified in the xattr.
706 */
707 rootkuid = mapped_kuid_fs(mnt_userns, fs_ns, rootkuid);
708 if (!rootid_owns_currentns(rootkuid))
709 return -ENODATA;
710
711 CAP_FOR_EACH_U32(i) {
712 if (i >= tocopy)
713 break;
714 cpu_caps->permitted.cap[i] = le32_to_cpu(caps->data[i].permitted);
715 cpu_caps->inheritable.cap[i] = le32_to_cpu(caps->data[i].inheritable);
716 }
717
718 cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
719 cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
720
721 cpu_caps->rootid = rootkuid;
722
723 return 0;
724 }
725
726 /*
727 * Attempt to get the on-exec apply capability sets for an executable file from
728 * its xattrs and, if present, apply them to the proposed credentials being
729 * constructed by execve().
730 */
get_file_caps(struct linux_binprm * bprm,struct file * file,bool * effective,bool * has_fcap)731 static int get_file_caps(struct linux_binprm *bprm, struct file *file,
732 bool *effective, bool *has_fcap)
733 {
734 int rc = 0;
735 struct cpu_vfs_cap_data vcaps;
736
737 cap_clear(bprm->cred->cap_permitted);
738
739 if (!file_caps_enabled)
740 return 0;
741
742 if (!mnt_may_suid(file->f_path.mnt))
743 return 0;
744
745 /*
746 * This check is redundant with mnt_may_suid() but is kept to make
747 * explicit that capability bits are limited to s_user_ns and its
748 * descendants.
749 */
750 if (!current_in_userns(file->f_path.mnt->mnt_sb->s_user_ns))
751 return 0;
752
753 rc = get_vfs_caps_from_disk(file_mnt_user_ns(file),
754 file->f_path.dentry, &vcaps);
755 if (rc < 0) {
756 if (rc == -EINVAL)
757 printk(KERN_NOTICE "Invalid argument reading file caps for %s\n",
758 bprm->filename);
759 else if (rc == -ENODATA)
760 rc = 0;
761 goto out;
762 }
763
764 rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_fcap);
765
766 out:
767 if (rc)
768 cap_clear(bprm->cred->cap_permitted);
769
770 return rc;
771 }
772
root_privileged(void)773 static inline bool root_privileged(void) { return !issecure(SECURE_NOROOT); }
774
__is_real(kuid_t uid,struct cred * cred)775 static inline bool __is_real(kuid_t uid, struct cred *cred)
776 { return uid_eq(cred->uid, uid); }
777
__is_eff(kuid_t uid,struct cred * cred)778 static inline bool __is_eff(kuid_t uid, struct cred *cred)
779 { return uid_eq(cred->euid, uid); }
780
__is_suid(kuid_t uid,struct cred * cred)781 static inline bool __is_suid(kuid_t uid, struct cred *cred)
782 { return !__is_real(uid, cred) && __is_eff(uid, cred); }
783
784 /*
785 * handle_privileged_root - Handle case of privileged root
786 * @bprm: The execution parameters, including the proposed creds
787 * @has_fcap: Are any file capabilities set?
788 * @effective: Do we have effective root privilege?
789 * @root_uid: This namespace' root UID WRT initial USER namespace
790 *
791 * Handle the case where root is privileged and hasn't been neutered by
792 * SECURE_NOROOT. If file capabilities are set, they won't be combined with
793 * set UID root and nothing is changed. If we are root, cap_permitted is
794 * updated. If we have become set UID root, the effective bit is set.
795 */
handle_privileged_root(struct linux_binprm * bprm,bool has_fcap,bool * effective,kuid_t root_uid)796 static void handle_privileged_root(struct linux_binprm *bprm, bool has_fcap,
797 bool *effective, kuid_t root_uid)
798 {
799 const struct cred *old = current_cred();
800 struct cred *new = bprm->cred;
801
802 if (!root_privileged())
803 return;
804 /*
805 * If the legacy file capability is set, then don't set privs
806 * for a setuid root binary run by a non-root user. Do set it
807 * for a root user just to cause least surprise to an admin.
808 */
809 if (has_fcap && __is_suid(root_uid, new)) {
810 warn_setuid_and_fcaps_mixed(bprm->filename);
811 return;
812 }
813 /*
814 * To support inheritance of root-permissions and suid-root
815 * executables under compatibility mode, we override the
816 * capability sets for the file.
817 */
818 if (__is_eff(root_uid, new) || __is_real(root_uid, new)) {
819 /* pP' = (cap_bset & ~0) | (pI & ~0) */
820 new->cap_permitted = cap_combine(old->cap_bset,
821 old->cap_inheritable);
822 }
823 /*
824 * If only the real uid is 0, we do not set the effective bit.
825 */
826 if (__is_eff(root_uid, new))
827 *effective = true;
828 }
829
830 #define __cap_gained(field, target, source) \
831 !cap_issubset(target->cap_##field, source->cap_##field)
832 #define __cap_grew(target, source, cred) \
833 !cap_issubset(cred->cap_##target, cred->cap_##source)
834 #define __cap_full(field, cred) \
835 cap_issubset(CAP_FULL_SET, cred->cap_##field)
836
__is_setuid(struct cred * new,const struct cred * old)837 static inline bool __is_setuid(struct cred *new, const struct cred *old)
838 { return !uid_eq(new->euid, old->uid); }
839
__is_setgid(struct cred * new,const struct cred * old)840 static inline bool __is_setgid(struct cred *new, const struct cred *old)
841 { return !gid_eq(new->egid, old->gid); }
842
843 /*
844 * 1) Audit candidate if current->cap_effective is set
845 *
846 * We do not bother to audit if 3 things are true:
847 * 1) cap_effective has all caps
848 * 2) we became root *OR* are were already root
849 * 3) root is supposed to have all caps (SECURE_NOROOT)
850 * Since this is just a normal root execing a process.
851 *
852 * Number 1 above might fail if you don't have a full bset, but I think
853 * that is interesting information to audit.
854 *
855 * A number of other conditions require logging:
856 * 2) something prevented setuid root getting all caps
857 * 3) non-setuid root gets fcaps
858 * 4) non-setuid root gets ambient
859 */
nonroot_raised_pE(struct cred * new,const struct cred * old,kuid_t root,bool has_fcap)860 static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old,
861 kuid_t root, bool has_fcap)
862 {
863 bool ret = false;
864
865 if ((__cap_grew(effective, ambient, new) &&
866 !(__cap_full(effective, new) &&
867 (__is_eff(root, new) || __is_real(root, new)) &&
868 root_privileged())) ||
869 (root_privileged() &&
870 __is_suid(root, new) &&
871 !__cap_full(effective, new)) ||
872 (!__is_setuid(new, old) &&
873 ((has_fcap &&
874 __cap_gained(permitted, new, old)) ||
875 __cap_gained(ambient, new, old))))
876
877 ret = true;
878
879 return ret;
880 }
881
882 /**
883 * cap_bprm_creds_from_file - Set up the proposed credentials for execve().
884 * @bprm: The execution parameters, including the proposed creds
885 * @file: The file to pull the credentials from
886 *
887 * Set up the proposed credentials for a new execution context being
888 * constructed by execve(). The proposed creds in @bprm->cred is altered,
889 * which won't take effect immediately.
890 *
891 * Return: 0 if successful, -ve on error.
892 */
cap_bprm_creds_from_file(struct linux_binprm * bprm,struct file * file)893 int cap_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file)
894 {
895 /* Process setpcap binaries and capabilities for uid 0 */
896 const struct cred *old = current_cred();
897 struct cred *new = bprm->cred;
898 bool effective = false, has_fcap = false, is_setid;
899 int ret;
900 kuid_t root_uid;
901
902 if (WARN_ON(!cap_ambient_invariant_ok(old)))
903 return -EPERM;
904
905 ret = get_file_caps(bprm, file, &effective, &has_fcap);
906 if (ret < 0)
907 return ret;
908
909 root_uid = make_kuid(new->user_ns, 0);
910
911 handle_privileged_root(bprm, has_fcap, &effective, root_uid);
912
913 /* if we have fs caps, clear dangerous personality flags */
914 if (__cap_gained(permitted, new, old))
915 bprm->per_clear |= PER_CLEAR_ON_SETID;
916
917 /* Don't let someone trace a set[ug]id/setpcap binary with the revised
918 * credentials unless they have the appropriate permit.
919 *
920 * In addition, if NO_NEW_PRIVS, then ensure we get no new privs.
921 */
922 is_setid = __is_setuid(new, old) || __is_setgid(new, old);
923
924 if ((is_setid || __cap_gained(permitted, new, old)) &&
925 ((bprm->unsafe & ~LSM_UNSAFE_PTRACE) ||
926 !ptracer_capable(current, new->user_ns))) {
927 /* downgrade; they get no more than they had, and maybe less */
928 if (!ns_capable(new->user_ns, CAP_SETUID) ||
929 (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) {
930 new->euid = new->uid;
931 new->egid = new->gid;
932 }
933 new->cap_permitted = cap_intersect(new->cap_permitted,
934 old->cap_permitted);
935 }
936
937 new->suid = new->fsuid = new->euid;
938 new->sgid = new->fsgid = new->egid;
939
940 /* File caps or setid cancels ambient. */
941 if (has_fcap || is_setid)
942 cap_clear(new->cap_ambient);
943
944 /*
945 * Now that we've computed pA', update pP' to give:
946 * pP' = (X & fP) | (pI & fI) | pA'
947 */
948 new->cap_permitted = cap_combine(new->cap_permitted, new->cap_ambient);
949
950 /*
951 * Set pE' = (fE ? pP' : pA'). Because pA' is zero if fE is set,
952 * this is the same as pE' = (fE ? pP' : 0) | pA'.
953 */
954 if (effective)
955 new->cap_effective = new->cap_permitted;
956 else
957 new->cap_effective = new->cap_ambient;
958
959 if (WARN_ON(!cap_ambient_invariant_ok(new)))
960 return -EPERM;
961
962 if (nonroot_raised_pE(new, old, root_uid, has_fcap)) {
963 ret = audit_log_bprm_fcaps(bprm, new, old);
964 if (ret < 0)
965 return ret;
966 }
967
968 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
969
970 if (WARN_ON(!cap_ambient_invariant_ok(new)))
971 return -EPERM;
972
973 /* Check for privilege-elevated exec. */
974 if (is_setid ||
975 (!__is_real(root_uid, new) &&
976 (effective ||
977 __cap_grew(permitted, ambient, new))))
978 bprm->secureexec = 1;
979
980 return 0;
981 }
982
983 /**
984 * cap_inode_setxattr - Determine whether an xattr may be altered
985 * @dentry: The inode/dentry being altered
986 * @name: The name of the xattr to be changed
987 * @value: The value that the xattr will be changed to
988 * @size: The size of value
989 * @flags: The replacement flag
990 *
991 * Determine whether an xattr may be altered or set on an inode, returning 0 if
992 * permission is granted, -ve if denied.
993 *
994 * This is used to make sure security xattrs don't get updated or set by those
995 * who aren't privileged to do so.
996 */
cap_inode_setxattr(struct dentry * dentry,const char * name,const void * value,size_t size,int flags)997 int cap_inode_setxattr(struct dentry *dentry, const char *name,
998 const void *value, size_t size, int flags)
999 {
1000 struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
1001
1002 /* Ignore non-security xattrs */
1003 if (strncmp(name, XATTR_SECURITY_PREFIX,
1004 XATTR_SECURITY_PREFIX_LEN) != 0)
1005 return 0;
1006
1007 /*
1008 * For XATTR_NAME_CAPS the check will be done in
1009 * cap_convert_nscap(), called by setxattr()
1010 */
1011 if (strcmp(name, XATTR_NAME_CAPS) == 0)
1012 return 0;
1013
1014 if (!ns_capable(user_ns, CAP_SYS_ADMIN))
1015 return -EPERM;
1016 return 0;
1017 }
1018
1019 /**
1020 * cap_inode_removexattr - Determine whether an xattr may be removed
1021 *
1022 * @mnt_userns: User namespace of the mount the inode was found from
1023 * @dentry: The inode/dentry being altered
1024 * @name: The name of the xattr to be changed
1025 *
1026 * Determine whether an xattr may be removed from an inode, returning 0 if
1027 * permission is granted, -ve if denied.
1028 *
1029 * If the inode has been found through an idmapped mount the user namespace of
1030 * the vfsmount must be passed through @mnt_userns. This function will then
1031 * take care to map the inode according to @mnt_userns before checking
1032 * permissions. On non-idmapped mounts or if permission checking is to be
1033 * performed on the raw inode simply passs init_user_ns.
1034 *
1035 * This is used to make sure security xattrs don't get removed by those who
1036 * aren't privileged to remove them.
1037 */
cap_inode_removexattr(struct user_namespace * mnt_userns,struct dentry * dentry,const char * name)1038 int cap_inode_removexattr(struct user_namespace *mnt_userns,
1039 struct dentry *dentry, const char *name)
1040 {
1041 struct user_namespace *user_ns = dentry->d_sb->s_user_ns;
1042
1043 /* Ignore non-security xattrs */
1044 if (strncmp(name, XATTR_SECURITY_PREFIX,
1045 XATTR_SECURITY_PREFIX_LEN) != 0)
1046 return 0;
1047
1048 if (strcmp(name, XATTR_NAME_CAPS) == 0) {
1049 /* security.capability gets namespaced */
1050 struct inode *inode = d_backing_inode(dentry);
1051 if (!inode)
1052 return -EINVAL;
1053 if (!capable_wrt_inode_uidgid(mnt_userns, inode, CAP_SETFCAP))
1054 return -EPERM;
1055 return 0;
1056 }
1057
1058 if (!ns_capable(user_ns, CAP_SYS_ADMIN))
1059 return -EPERM;
1060 return 0;
1061 }
1062
1063 /*
1064 * cap_emulate_setxuid() fixes the effective / permitted capabilities of
1065 * a process after a call to setuid, setreuid, or setresuid.
1066 *
1067 * 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
1068 * {r,e,s}uid != 0, the permitted and effective capabilities are
1069 * cleared.
1070 *
1071 * 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
1072 * capabilities of the process are cleared.
1073 *
1074 * 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
1075 * capabilities are set to the permitted capabilities.
1076 *
1077 * fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
1078 * never happen.
1079 *
1080 * -astor
1081 *
1082 * cevans - New behaviour, Oct '99
1083 * A process may, via prctl(), elect to keep its capabilities when it
1084 * calls setuid() and switches away from uid==0. Both permitted and
1085 * effective sets will be retained.
1086 * Without this change, it was impossible for a daemon to drop only some
1087 * of its privilege. The call to setuid(!=0) would drop all privileges!
1088 * Keeping uid 0 is not an option because uid 0 owns too many vital
1089 * files..
1090 * Thanks to Olaf Kirch and Peter Benie for spotting this.
1091 */
cap_emulate_setxuid(struct cred * new,const struct cred * old)1092 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
1093 {
1094 kuid_t root_uid = make_kuid(old->user_ns, 0);
1095
1096 if ((uid_eq(old->uid, root_uid) ||
1097 uid_eq(old->euid, root_uid) ||
1098 uid_eq(old->suid, root_uid)) &&
1099 (!uid_eq(new->uid, root_uid) &&
1100 !uid_eq(new->euid, root_uid) &&
1101 !uid_eq(new->suid, root_uid))) {
1102 if (!issecure(SECURE_KEEP_CAPS)) {
1103 cap_clear(new->cap_permitted);
1104 cap_clear(new->cap_effective);
1105 }
1106
1107 /*
1108 * Pre-ambient programs expect setresuid to nonroot followed
1109 * by exec to drop capabilities. We should make sure that
1110 * this remains the case.
1111 */
1112 cap_clear(new->cap_ambient);
1113 }
1114 if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
1115 cap_clear(new->cap_effective);
1116 if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
1117 new->cap_effective = new->cap_permitted;
1118 }
1119
1120 /**
1121 * cap_task_fix_setuid - Fix up the results of setuid() call
1122 * @new: The proposed credentials
1123 * @old: The current task's current credentials
1124 * @flags: Indications of what has changed
1125 *
1126 * Fix up the results of setuid() call before the credential changes are
1127 * actually applied.
1128 *
1129 * Return: 0 to grant the changes, -ve to deny them.
1130 */
cap_task_fix_setuid(struct cred * new,const struct cred * old,int flags)1131 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
1132 {
1133 switch (flags) {
1134 case LSM_SETID_RE:
1135 case LSM_SETID_ID:
1136 case LSM_SETID_RES:
1137 /* juggle the capabilities to follow [RES]UID changes unless
1138 * otherwise suppressed */
1139 if (!issecure(SECURE_NO_SETUID_FIXUP))
1140 cap_emulate_setxuid(new, old);
1141 break;
1142
1143 case LSM_SETID_FS:
1144 /* juggle the capabilties to follow FSUID changes, unless
1145 * otherwise suppressed
1146 *
1147 * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
1148 * if not, we might be a bit too harsh here.
1149 */
1150 if (!issecure(SECURE_NO_SETUID_FIXUP)) {
1151 kuid_t root_uid = make_kuid(old->user_ns, 0);
1152 if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
1153 new->cap_effective =
1154 cap_drop_fs_set(new->cap_effective);
1155
1156 if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
1157 new->cap_effective =
1158 cap_raise_fs_set(new->cap_effective,
1159 new->cap_permitted);
1160 }
1161 break;
1162
1163 default:
1164 return -EINVAL;
1165 }
1166
1167 return 0;
1168 }
1169
1170 /*
1171 * Rationale: code calling task_setscheduler, task_setioprio, and
1172 * task_setnice, assumes that
1173 * . if capable(cap_sys_nice), then those actions should be allowed
1174 * . if not capable(cap_sys_nice), but acting on your own processes,
1175 * then those actions should be allowed
1176 * This is insufficient now since you can call code without suid, but
1177 * yet with increased caps.
1178 * So we check for increased caps on the target process.
1179 */
cap_safe_nice(struct task_struct * p)1180 static int cap_safe_nice(struct task_struct *p)
1181 {
1182 int is_subset, ret = 0;
1183
1184 rcu_read_lock();
1185 is_subset = cap_issubset(__task_cred(p)->cap_permitted,
1186 current_cred()->cap_permitted);
1187 if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
1188 ret = -EPERM;
1189 rcu_read_unlock();
1190
1191 return ret;
1192 }
1193
1194 /**
1195 * cap_task_setscheduler - Detemine if scheduler policy change is permitted
1196 * @p: The task to affect
1197 *
1198 * Detemine if the requested scheduler policy change is permitted for the
1199 * specified task.
1200 *
1201 * Return: 0 if permission is granted, -ve if denied.
1202 */
cap_task_setscheduler(struct task_struct * p)1203 int cap_task_setscheduler(struct task_struct *p)
1204 {
1205 return cap_safe_nice(p);
1206 }
1207
1208 /**
1209 * cap_task_setioprio - Detemine if I/O priority change is permitted
1210 * @p: The task to affect
1211 * @ioprio: The I/O priority to set
1212 *
1213 * Detemine if the requested I/O priority change is permitted for the specified
1214 * task.
1215 *
1216 * Return: 0 if permission is granted, -ve if denied.
1217 */
cap_task_setioprio(struct task_struct * p,int ioprio)1218 int cap_task_setioprio(struct task_struct *p, int ioprio)
1219 {
1220 return cap_safe_nice(p);
1221 }
1222
1223 /**
1224 * cap_task_setnice - Detemine if task priority change is permitted
1225 * @p: The task to affect
1226 * @nice: The nice value to set
1227 *
1228 * Detemine if the requested task priority change is permitted for the
1229 * specified task.
1230 *
1231 * Return: 0 if permission is granted, -ve if denied.
1232 */
cap_task_setnice(struct task_struct * p,int nice)1233 int cap_task_setnice(struct task_struct *p, int nice)
1234 {
1235 return cap_safe_nice(p);
1236 }
1237
1238 /*
1239 * Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from
1240 * the current task's bounding set. Returns 0 on success, -ve on error.
1241 */
cap_prctl_drop(unsigned long cap)1242 static int cap_prctl_drop(unsigned long cap)
1243 {
1244 struct cred *new;
1245
1246 if (!ns_capable(current_user_ns(), CAP_SETPCAP))
1247 return -EPERM;
1248 if (!cap_valid(cap))
1249 return -EINVAL;
1250
1251 new = prepare_creds();
1252 if (!new)
1253 return -ENOMEM;
1254 cap_lower(new->cap_bset, cap);
1255 return commit_creds(new);
1256 }
1257
1258 /**
1259 * cap_task_prctl - Implement process control functions for this security module
1260 * @option: The process control function requested
1261 * @arg2: The argument data for this function
1262 * @arg3: The argument data for this function
1263 * @arg4: The argument data for this function
1264 * @arg5: The argument data for this function
1265 *
1266 * Allow process control functions (sys_prctl()) to alter capabilities; may
1267 * also deny access to other functions not otherwise implemented here.
1268 *
1269 * Return: 0 or +ve on success, -ENOSYS if this function is not implemented
1270 * here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM
1271 * modules will consider performing the function.
1272 */
cap_task_prctl(int option,unsigned long arg2,unsigned long arg3,unsigned long arg4,unsigned long arg5)1273 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
1274 unsigned long arg4, unsigned long arg5)
1275 {
1276 const struct cred *old = current_cred();
1277 struct cred *new;
1278
1279 switch (option) {
1280 case PR_CAPBSET_READ:
1281 if (!cap_valid(arg2))
1282 return -EINVAL;
1283 return !!cap_raised(old->cap_bset, arg2);
1284
1285 case PR_CAPBSET_DROP:
1286 return cap_prctl_drop(arg2);
1287
1288 /*
1289 * The next four prctl's remain to assist with transitioning a
1290 * system from legacy UID=0 based privilege (when filesystem
1291 * capabilities are not in use) to a system using filesystem
1292 * capabilities only - as the POSIX.1e draft intended.
1293 *
1294 * Note:
1295 *
1296 * PR_SET_SECUREBITS =
1297 * issecure_mask(SECURE_KEEP_CAPS_LOCKED)
1298 * | issecure_mask(SECURE_NOROOT)
1299 * | issecure_mask(SECURE_NOROOT_LOCKED)
1300 * | issecure_mask(SECURE_NO_SETUID_FIXUP)
1301 * | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
1302 *
1303 * will ensure that the current process and all of its
1304 * children will be locked into a pure
1305 * capability-based-privilege environment.
1306 */
1307 case PR_SET_SECUREBITS:
1308 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
1309 & (old->securebits ^ arg2)) /*[1]*/
1310 || ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
1311 || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
1312 || (cap_capable(current_cred(),
1313 current_cred()->user_ns,
1314 CAP_SETPCAP,
1315 CAP_OPT_NONE) != 0) /*[4]*/
1316 /*
1317 * [1] no changing of bits that are locked
1318 * [2] no unlocking of locks
1319 * [3] no setting of unsupported bits
1320 * [4] doing anything requires privilege (go read about
1321 * the "sendmail capabilities bug")
1322 */
1323 )
1324 /* cannot change a locked bit */
1325 return -EPERM;
1326
1327 new = prepare_creds();
1328 if (!new)
1329 return -ENOMEM;
1330 new->securebits = arg2;
1331 return commit_creds(new);
1332
1333 case PR_GET_SECUREBITS:
1334 return old->securebits;
1335
1336 case PR_GET_KEEPCAPS:
1337 return !!issecure(SECURE_KEEP_CAPS);
1338
1339 case PR_SET_KEEPCAPS:
1340 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
1341 return -EINVAL;
1342 if (issecure(SECURE_KEEP_CAPS_LOCKED))
1343 return -EPERM;
1344
1345 new = prepare_creds();
1346 if (!new)
1347 return -ENOMEM;
1348 if (arg2)
1349 new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
1350 else
1351 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
1352 return commit_creds(new);
1353
1354 case PR_CAP_AMBIENT:
1355 if (arg2 == PR_CAP_AMBIENT_CLEAR_ALL) {
1356 if (arg3 | arg4 | arg5)
1357 return -EINVAL;
1358
1359 new = prepare_creds();
1360 if (!new)
1361 return -ENOMEM;
1362 cap_clear(new->cap_ambient);
1363 return commit_creds(new);
1364 }
1365
1366 if (((!cap_valid(arg3)) | arg4 | arg5))
1367 return -EINVAL;
1368
1369 if (arg2 == PR_CAP_AMBIENT_IS_SET) {
1370 return !!cap_raised(current_cred()->cap_ambient, arg3);
1371 } else if (arg2 != PR_CAP_AMBIENT_RAISE &&
1372 arg2 != PR_CAP_AMBIENT_LOWER) {
1373 return -EINVAL;
1374 } else {
1375 if (arg2 == PR_CAP_AMBIENT_RAISE &&
1376 (!cap_raised(current_cred()->cap_permitted, arg3) ||
1377 !cap_raised(current_cred()->cap_inheritable,
1378 arg3) ||
1379 issecure(SECURE_NO_CAP_AMBIENT_RAISE)))
1380 return -EPERM;
1381
1382 new = prepare_creds();
1383 if (!new)
1384 return -ENOMEM;
1385 if (arg2 == PR_CAP_AMBIENT_RAISE)
1386 cap_raise(new->cap_ambient, arg3);
1387 else
1388 cap_lower(new->cap_ambient, arg3);
1389 return commit_creds(new);
1390 }
1391
1392 default:
1393 /* No functionality available - continue with default */
1394 return -ENOSYS;
1395 }
1396 }
1397
1398 /**
1399 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
1400 * @mm: The VM space in which the new mapping is to be made
1401 * @pages: The size of the mapping
1402 *
1403 * Determine whether the allocation of a new virtual mapping by the current
1404 * task is permitted.
1405 *
1406 * Return: 1 if permission is granted, 0 if not.
1407 */
cap_vm_enough_memory(struct mm_struct * mm,long pages)1408 int cap_vm_enough_memory(struct mm_struct *mm, long pages)
1409 {
1410 int cap_sys_admin = 0;
1411
1412 if (cap_capable(current_cred(), &init_user_ns,
1413 CAP_SYS_ADMIN, CAP_OPT_NOAUDIT) == 0)
1414 cap_sys_admin = 1;
1415
1416 return cap_sys_admin;
1417 }
1418
1419 /**
1420 * cap_mmap_addr - check if able to map given addr
1421 * @addr: address attempting to be mapped
1422 *
1423 * If the process is attempting to map memory below dac_mmap_min_addr they need
1424 * CAP_SYS_RAWIO. The other parameters to this function are unused by the
1425 * capability security module.
1426 *
1427 * Return: 0 if this mapping should be allowed or -EPERM if not.
1428 */
cap_mmap_addr(unsigned long addr)1429 int cap_mmap_addr(unsigned long addr)
1430 {
1431 int ret = 0;
1432
1433 if (addr < dac_mmap_min_addr) {
1434 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
1435 CAP_OPT_NONE);
1436 /* set PF_SUPERPRIV if it turns out we allow the low mmap */
1437 if (ret == 0)
1438 current->flags |= PF_SUPERPRIV;
1439 }
1440 return ret;
1441 }
1442
cap_mmap_file(struct file * file,unsigned long reqprot,unsigned long prot,unsigned long flags)1443 int cap_mmap_file(struct file *file, unsigned long reqprot,
1444 unsigned long prot, unsigned long flags)
1445 {
1446 return 0;
1447 }
1448
1449 #ifdef CONFIG_SECURITY
1450
1451 static struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
1452 LSM_HOOK_INIT(capable, cap_capable),
1453 LSM_HOOK_INIT(settime, cap_settime),
1454 LSM_HOOK_INIT(ptrace_access_check, cap_ptrace_access_check),
1455 LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
1456 LSM_HOOK_INIT(capget, cap_capget),
1457 LSM_HOOK_INIT(capset, cap_capset),
1458 LSM_HOOK_INIT(bprm_creds_from_file, cap_bprm_creds_from_file),
1459 LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
1460 LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
1461 LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),
1462 LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),
1463 LSM_HOOK_INIT(mmap_file, cap_mmap_file),
1464 LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid),
1465 LSM_HOOK_INIT(task_prctl, cap_task_prctl),
1466 LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler),
1467 LSM_HOOK_INIT(task_setioprio, cap_task_setioprio),
1468 LSM_HOOK_INIT(task_setnice, cap_task_setnice),
1469 LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory),
1470 };
1471
capability_init(void)1472 static int __init capability_init(void)
1473 {
1474 security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks),
1475 "capability");
1476 return 0;
1477 }
1478
1479 DEFINE_LSM(capability) = {
1480 .name = "capability",
1481 .order = LSM_ORDER_FIRST,
1482 .init = capability_init,
1483 };
1484
1485 #endif /* CONFIG_SECURITY */
1486