Free Electrons

Embedded Linux Experts

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
/* Common capabilities, needed by capability.o.
 *
 *	This program is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU General Public License as published by
 *	the Free Software Foundation; either version 2 of the License, or
 *	(at your option) any later version.
 *
 */

#include <linux/capability.h>
#include <linux/audit.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/security.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/ptrace.h>
#include <linux/xattr.h>
#include <linux/hugetlb.h>
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/prctl.h>
#include <linux/securebits.h>
#include <linux/user_namespace.h>
#include <linux/binfmts.h>
#include <linux/personality.h>

/*
 * If a non-root user executes a setuid-root binary in
 * !secure(SECURE_NOROOT) mode, then we raise capabilities.
 * However if fE is also set, then the intent is for only
 * the file capabilities to be applied, and the setuid-root
 * bit is left on either to change the uid (plausible) or
 * to get full privilege on a kernel without file capabilities
 * support.  So in that case we do not raise capabilities.
 *
 * Warn if that happens, once per boot.
 */
static void warn_setuid_and_fcaps_mixed(const char *fname)
{
	static int warned;
	if (!warned) {
		printk(KERN_INFO "warning: `%s' has both setuid-root and"
			" effective capabilities. Therefore not raising all"
			" capabilities.\n", fname);
		warned = 1;
	}
}

int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
{
	return 0;
}

/**
 * cap_capable - Determine whether a task has a particular effective capability
 * @cred: The credentials to use
 * @ns:  The user namespace in which we need the capability
 * @cap: The capability to check for
 * @audit: Whether to write an audit message or not
 *
 * Determine whether the nominated task has the specified capability amongst
 * its effective set, returning 0 if it does, -ve if it does not.
 *
 * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
 * and has_capability() functions.  That is, it has the reverse semantics:
 * cap_has_capability() returns 0 when a task has a capability, but the
 * kernel's capable() and has_capability() returns 1 for this case.
 */
int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
		int cap, int audit)
{
	struct user_namespace *ns = targ_ns;

	/* See if cred has the capability in the target user namespace
	 * by examining the target user namespace and all of the target
	 * user namespace's parents.
	 */
	for (;;) {
		/* Do we have the necessary capabilities? */
		if (ns == cred->user_ns)
			return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;

		/* Have we tried all of the parent namespaces? */
		if (ns == &init_user_ns)
			return -EPERM;

		/* 
		 * The owner of the user namespace in the parent of the
		 * user namespace has all caps.
		 */
		if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
			return 0;

		/*
		 * If you have a capability in a parent user ns, then you have
		 * it over all children user namespaces as well.
		 */
		ns = ns->parent;
	}

	/* We never get here */
}

/**
 * cap_settime - Determine whether the current process may set the system clock
 * @ts: The time to set
 * @tz: The timezone to set
 *
 * Determine whether the current process may set the system clock and timezone
 * information, returning 0 if permission granted, -ve if denied.
 */
int cap_settime(const struct timespec *ts, const struct timezone *tz)
{
	if (!capable(CAP_SYS_TIME))
		return -EPERM;
	return 0;
}

/**
 * cap_ptrace_access_check - Determine whether the current process may access
 *			   another
 * @child: The process to be accessed
 * @mode: The mode of attachment.
 *
 * If we are in the same or an ancestor user_ns and have all the target
 * task's capabilities, then ptrace access is allowed.
 * If we have the ptrace capability to the target user_ns, then ptrace
 * access is allowed.
 * Else denied.
 *
 * Determine whether a process may access another, returning 0 if permission
 * granted, -ve if denied.
 */
int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
{
	int ret = 0;
	const struct cred *cred, *child_cred;

	rcu_read_lock();
	cred = current_cred();
	child_cred = __task_cred(child);
	if (cred->user_ns == child_cred->user_ns &&
	    cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
		goto out;
	if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
		goto out;
	ret = -EPERM;
out:
	rcu_read_unlock();
	return ret;
}

/**
 * cap_ptrace_traceme - Determine whether another process may trace the current
 * @parent: The task proposed to be the tracer
 *
 * If parent is in the same or an ancestor user_ns and has all current's
 * capabilities, then ptrace access is allowed.
 * If parent has the ptrace capability to current's user_ns, then ptrace
 * access is allowed.
 * Else denied.
 *
 * Determine whether the nominated task is permitted to trace the current
 * process, returning 0 if permission is granted, -ve if denied.
 */
int cap_ptrace_traceme(struct task_struct *parent)
{
	int ret = 0;
	const struct cred *cred, *child_cred;

	rcu_read_lock();
	cred = __task_cred(parent);
	child_cred = current_cred();
	if (cred->user_ns == child_cred->user_ns &&
	    cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
		goto out;
	if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE))
		goto out;
	ret = -EPERM;
out:
	rcu_read_unlock();
	return ret;
}

/**
 * cap_capget - Retrieve a task's capability sets
 * @target: The task from which to retrieve the capability sets
 * @effective: The place to record the effective set
 * @inheritable: The place to record the inheritable set
 * @permitted: The place to record the permitted set
 *
 * This function retrieves the capabilities of the nominated task and returns
 * them to the caller.
 */
int cap_capget(struct task_struct *target, kernel_cap_t *effective,
	       kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
	const struct cred *cred;

	/* Derived from kernel/capability.c:sys_capget. */
	rcu_read_lock();
	cred = __task_cred(target);
	*effective   = cred->cap_effective;
	*inheritable = cred->cap_inheritable;
	*permitted   = cred->cap_permitted;
	rcu_read_unlock();
	return 0;
}

/*
 * Determine whether the inheritable capabilities are limited to the old
 * permitted set.  Returns 1 if they are limited, 0 if they are not.
 */
static inline int cap_inh_is_capped(void)
{

	/* they are so limited unless the current task has the CAP_SETPCAP
	 * capability
	 */
	if (cap_capable(current_cred(), current_cred()->user_ns,
			CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
		return 0;
	return 1;
}

/**
 * cap_capset - Validate and apply proposed changes to current's capabilities
 * @new: The proposed new credentials; alterations should be made here
 * @old: The current task's current credentials
 * @effective: A pointer to the proposed new effective capabilities set
 * @inheritable: A pointer to the proposed new inheritable capabilities set
 * @permitted: A pointer to the proposed new permitted capabilities set
 *
 * This function validates and applies a proposed mass change to the current
 * process's capability sets.  The changes are made to the proposed new
 * credentials, and assuming no error, will be committed by the caller of LSM.
 */
int cap_capset(struct cred *new,
	       const struct cred *old,
	       const kernel_cap_t *effective,
	       const kernel_cap_t *inheritable,
	       const kernel_cap_t *permitted)
{
	if (cap_inh_is_capped() &&
	    !cap_issubset(*inheritable,
			  cap_combine(old->cap_inheritable,
				      old->cap_permitted)))
		/* incapable of using this inheritable set */
		return -EPERM;

	if (!cap_issubset(*inheritable,
			  cap_combine(old->cap_inheritable,
				      old->cap_bset)))
		/* no new pI capabilities outside bounding set */
		return -EPERM;

	/* verify restrictions on target's new Permitted set */
	if (!cap_issubset(*permitted, old->cap_permitted))
		return -EPERM;

	/* verify the _new_Effective_ is a subset of the _new_Permitted_ */
	if (!cap_issubset(*effective, *permitted))
		return -EPERM;

	new->cap_effective   = *effective;
	new->cap_inheritable = *inheritable;
	new->cap_permitted   = *permitted;
	return 0;
}

/*
 * Clear proposed capability sets for execve().
 */
static inline void bprm_clear_caps(struct linux_binprm *bprm)
{
	cap_clear(bprm->cred->cap_permitted);
	bprm->cap_effective = false;
}

/**
 * cap_inode_need_killpriv - Determine if inode change affects privileges
 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
 *
 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
 * affects the security markings on that inode, and if it is, should
 * inode_killpriv() be invoked or the change rejected?
 *
 * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and
 * -ve to deny the change.
 */
int cap_inode_need_killpriv(struct dentry *dentry)
{
	struct inode *inode = d_backing_inode(dentry);
	int error;

	if (!inode->i_op->getxattr)
	       return 0;

	error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0);
	if (error <= 0)
		return 0;
	return 1;
}

/**
 * cap_inode_killpriv - Erase the security markings on an inode
 * @dentry: The inode/dentry to alter
 *
 * Erase the privilege-enhancing security markings on an inode.
 *
 * Returns 0 if successful, -ve on error.
 */
int cap_inode_killpriv(struct dentry *dentry)
{
	struct inode *inode = d_backing_inode(dentry);

	if (!inode->i_op->removexattr)
	       return 0;

	return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
}

/*
 * Calculate the new process capability sets from the capability sets attached
 * to a file.
 */
static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
					  struct linux_binprm *bprm,
					  bool *effective,
					  bool *has_cap)
{
	struct cred *new = bprm->cred;
	unsigned i;
	int ret = 0;

	if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
		*effective = true;

	if (caps->magic_etc & VFS_CAP_REVISION_MASK)
		*has_cap = true;

	CAP_FOR_EACH_U32(i) {
		__u32 permitted = caps->permitted.cap[i];
		__u32 inheritable = caps->inheritable.cap[i];

		/*
		 * pP' = (X & fP) | (pI & fI)
		 */
		new->cap_permitted.cap[i] =
			(new->cap_bset.cap[i] & permitted) |
			(new->cap_inheritable.cap[i] & inheritable);

		if (permitted & ~new->cap_permitted.cap[i])
			/* insufficient to execute correctly */
			ret = -EPERM;
	}

	/*
	 * For legacy apps, with no internal support for recognizing they
	 * do not have enough capabilities, we return an error if they are
	 * missing some "forced" (aka file-permitted) capabilities.
	 */
	return *effective ? ret : 0;
}

/*
 * Extract the on-exec-apply capability sets for an executable file.
 */
int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
{
	struct inode *inode = d_backing_inode(dentry);
	__u32 magic_etc;
	unsigned tocopy, i;
	int size;
	struct vfs_cap_data caps;

	memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));

	if (!inode || !inode->i_op->getxattr)
		return -ENODATA;

	size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps,
				   XATTR_CAPS_SZ);
	if (size == -ENODATA || size == -EOPNOTSUPP)
		/* no data, that's ok */
		return -ENODATA;
	if (size < 0)
		return size;

	if (size < sizeof(magic_etc))
		return -EINVAL;

	cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc);

	switch (magic_etc & VFS_CAP_REVISION_MASK) {
	case VFS_CAP_REVISION_1:
		if (size != XATTR_CAPS_SZ_1)
			return -EINVAL;
		tocopy = VFS_CAP_U32_1;
		break;
	case VFS_CAP_REVISION_2:
		if (size != XATTR_CAPS_SZ_2)
			return -EINVAL;
		tocopy = VFS_CAP_U32_2;
		break;
	default:
		return -EINVAL;
	}

	CAP_FOR_EACH_U32(i) {
		if (i >= tocopy)
			break;
		cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted);
		cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable);
	}

	cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
	cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;

	return 0;
}

/*
 * Attempt to get the on-exec apply capability sets for an executable file from
 * its xattrs and, if present, apply them to the proposed credentials being
 * constructed by execve().
 */
static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap)
{
	int rc = 0;
	struct cpu_vfs_cap_data vcaps;

	bprm_clear_caps(bprm);

	if (!file_caps_enabled)
		return 0;

	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
		return 0;

	rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
	if (rc < 0) {
		if (rc == -EINVAL)
			printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
				__func__, rc, bprm->filename);
		else if (rc == -ENODATA)
			rc = 0;
		goto out;
	}

	rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap);
	if (rc == -EINVAL)
		printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
		       __func__, rc, bprm->filename);

out:
	if (rc)
		bprm_clear_caps(bprm);

	return rc;
}

/**
 * cap_bprm_set_creds - Set up the proposed credentials for execve().
 * @bprm: The execution parameters, including the proposed creds
 *
 * Set up the proposed credentials for a new execution context being
 * constructed by execve().  The proposed creds in @bprm->cred is altered,
 * which won't take effect immediately.  Returns 0 if successful, -ve on error.
 */
int cap_bprm_set_creds(struct linux_binprm *bprm)
{
	const struct cred *old = current_cred();
	struct cred *new = bprm->cred;
	bool effective, has_cap = false;
	int ret;
	kuid_t root_uid;

	effective = false;
	ret = get_file_caps(bprm, &effective, &has_cap);
	if (ret < 0)
		return ret;

	root_uid = make_kuid(new->user_ns, 0);

	if (!issecure(SECURE_NOROOT)) {
		/*
		 * If the legacy file capability is set, then don't set privs
		 * for a setuid root binary run by a non-root user.  Do set it
		 * for a root user just to cause least surprise to an admin.
		 */
		if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
			warn_setuid_and_fcaps_mixed(bprm->filename);
			goto skip;
		}
		/*
		 * To support inheritance of root-permissions and suid-root
		 * executables under compatibility mode, we override the
		 * capability sets for the file.
		 *
		 * If only the real uid is 0, we do not set the effective bit.
		 */
		if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
			/* pP' = (cap_bset & ~0) | (pI & ~0) */
			new->cap_permitted = cap_combine(old->cap_bset,
							 old->cap_inheritable);
		}
		if (uid_eq(new->euid, root_uid))
			effective = true;
	}
skip:

	/* if we have fs caps, clear dangerous personality flags */
	if (!cap_issubset(new->cap_permitted, old->cap_permitted))
		bprm->per_clear |= PER_CLEAR_ON_SETID;


	/* Don't let someone trace a set[ug]id/setpcap binary with the revised
	 * credentials unless they have the appropriate permit.
	 *
	 * In addition, if NO_NEW_PRIVS, then ensure we get no new privs.
	 */
	if ((!uid_eq(new->euid, old->uid) ||
	     !gid_eq(new->egid, old->gid) ||
	     !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
	    bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
		/* downgrade; they get no more than they had, and maybe less */
		if (!capable(CAP_SETUID) ||
		    (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) {
			new->euid = new->uid;
			new->egid = new->gid;
		}
		new->cap_permitted = cap_intersect(new->cap_permitted,
						   old->cap_permitted);
	}

	new->suid = new->fsuid = new->euid;
	new->sgid = new->fsgid = new->egid;

	if (effective)
		new->cap_effective = new->cap_permitted;
	else
		cap_clear(new->cap_effective);
	bprm->cap_effective = effective;

	/*
	 * Audit candidate if current->cap_effective is set
	 *
	 * We do not bother to audit if 3 things are true:
	 *   1) cap_effective has all caps
	 *   2) we are root
	 *   3) root is supposed to have all caps (SECURE_NOROOT)
	 * Since this is just a normal root execing a process.
	 *
	 * Number 1 above might fail if you don't have a full bset, but I think
	 * that is interesting information to audit.
	 */
	if (!cap_isclear(new->cap_effective)) {
		if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
		    !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
		    issecure(SECURE_NOROOT)) {
			ret = audit_log_bprm_fcaps(bprm, new, old);
			if (ret < 0)
				return ret;
		}
	}

	new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
	return 0;
}

/**
 * cap_bprm_secureexec - Determine whether a secure execution is required
 * @bprm: The execution parameters
 *
 * Determine whether a secure execution is required, return 1 if it is, and 0
 * if it is not.
 *
 * The credentials have been committed by this point, and so are no longer
 * available through @bprm->cred.
 */
int cap_bprm_secureexec(struct linux_binprm *bprm)
{
	const struct cred *cred = current_cred();
	kuid_t root_uid = make_kuid(cred->user_ns, 0);

	if (!uid_eq(cred->uid, root_uid)) {
		if (bprm->cap_effective)
			return 1;
		if (!cap_isclear(cred->cap_permitted))
			return 1;
	}

	return (!uid_eq(cred->euid, cred->uid) ||
		!gid_eq(cred->egid, cred->gid));
}

/**
 * cap_inode_setxattr - Determine whether an xattr may be altered
 * @dentry: The inode/dentry being altered
 * @name: The name of the xattr to be changed
 * @value: The value that the xattr will be changed to
 * @size: The size of value
 * @flags: The replacement flag
 *
 * Determine whether an xattr may be altered or set on an inode, returning 0 if
 * permission is granted, -ve if denied.
 *
 * This is used to make sure security xattrs don't get updated or set by those
 * who aren't privileged to do so.
 */
int cap_inode_setxattr(struct dentry *dentry, const char *name,
		       const void *value, size_t size, int flags)
{
	if (!strcmp(name, XATTR_NAME_CAPS)) {
		if (!capable(CAP_SETFCAP))
			return -EPERM;
		return 0;
	}

	if (!strncmp(name, XATTR_SECURITY_PREFIX,
		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
	    !capable(CAP_SYS_ADMIN))
		return -EPERM;
	return 0;
}

/**
 * cap_inode_removexattr - Determine whether an xattr may be removed
 * @dentry: The inode/dentry being altered
 * @name: The name of the xattr to be changed
 *
 * Determine whether an xattr may be removed from an inode, returning 0 if
 * permission is granted, -ve if denied.
 *
 * This is used to make sure security xattrs don't get removed by those who
 * aren't privileged to remove them.
 */
int cap_inode_removexattr(struct dentry *dentry, const char *name)
{
	if (!strcmp(name, XATTR_NAME_CAPS)) {
		if (!capable(CAP_SETFCAP))
			return -EPERM;
		return 0;
	}

	if (!strncmp(name, XATTR_SECURITY_PREFIX,
		     sizeof(XATTR_SECURITY_PREFIX) - 1) &&
	    !capable(CAP_SYS_ADMIN))
		return -EPERM;
	return 0;
}

/*
 * cap_emulate_setxuid() fixes the effective / permitted capabilities of
 * a process after a call to setuid, setreuid, or setresuid.
 *
 *  1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
 *  {r,e,s}uid != 0, the permitted and effective capabilities are
 *  cleared.
 *
 *  2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
 *  capabilities of the process are cleared.
 *
 *  3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
 *  capabilities are set to the permitted capabilities.
 *
 *  fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
 *  never happen.
 *
 *  -astor
 *
 * cevans - New behaviour, Oct '99
 * A process may, via prctl(), elect to keep its capabilities when it
 * calls setuid() and switches away from uid==0. Both permitted and
 * effective sets will be retained.
 * Without this change, it was impossible for a daemon to drop only some
 * of its privilege. The call to setuid(!=0) would drop all privileges!
 * Keeping uid 0 is not an option because uid 0 owns too many vital
 * files..
 * Thanks to Olaf Kirch and Peter Benie for spotting this.
 */
static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
{
	kuid_t root_uid = make_kuid(old->user_ns, 0);

	if ((uid_eq(old->uid, root_uid) ||
	     uid_eq(old->euid, root_uid) ||
	     uid_eq(old->suid, root_uid)) &&
	    (!uid_eq(new->uid, root_uid) &&
	     !uid_eq(new->euid, root_uid) &&
	     !uid_eq(new->suid, root_uid)) &&
	    !issecure(SECURE_KEEP_CAPS)) {
		cap_clear(new->cap_permitted);
		cap_clear(new->cap_effective);
	}
	if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
		cap_clear(new->cap_effective);
	if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
		new->cap_effective = new->cap_permitted;
}

/**
 * cap_task_fix_setuid - Fix up the results of setuid() call
 * @new: The proposed credentials
 * @old: The current task's current credentials
 * @flags: Indications of what has changed
 *
 * Fix up the results of setuid() call before the credential changes are
 * actually applied, returning 0 to grant the changes, -ve to deny them.
 */
int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
{
	switch (flags) {
	case LSM_SETID_RE:
	case LSM_SETID_ID:
	case LSM_SETID_RES:
		/* juggle the capabilities to follow [RES]UID changes unless
		 * otherwise suppressed */
		if (!issecure(SECURE_NO_SETUID_FIXUP))
			cap_emulate_setxuid(new, old);
		break;

	case LSM_SETID_FS:
		/* juggle the capabilties to follow FSUID changes, unless
		 * otherwise suppressed
		 *
		 * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
		 *          if not, we might be a bit too harsh here.
		 */
		if (!issecure(SECURE_NO_SETUID_FIXUP)) {
			kuid_t root_uid = make_kuid(old->user_ns, 0);
			if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
				new->cap_effective =
					cap_drop_fs_set(new->cap_effective);

			if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
				new->cap_effective =
					cap_raise_fs_set(new->cap_effective,
							 new->cap_permitted);
		}
		break;

	default:
		return -EINVAL;
	}

	return 0;
}

/*
 * Rationale: code calling task_setscheduler, task_setioprio, and
 * task_setnice, assumes that
 *   . if capable(cap_sys_nice), then those actions should be allowed
 *   . if not capable(cap_sys_nice), but acting on your own processes,
 *   	then those actions should be allowed
 * This is insufficient now since you can call code without suid, but
 * yet with increased caps.
 * So we check for increased caps on the target process.
 */
static int cap_safe_nice(struct task_struct *p)
{
	int is_subset, ret = 0;

	rcu_read_lock();
	is_subset = cap_issubset(__task_cred(p)->cap_permitted,
				 current_cred()->cap_permitted);
	if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
		ret = -EPERM;
	rcu_read_unlock();

	return ret;
}

/**
 * cap_task_setscheduler - Detemine if scheduler policy change is permitted
 * @p: The task to affect
 *
 * Detemine if the requested scheduler policy change is permitted for the
 * specified task, returning 0 if permission is granted, -ve if denied.
 */
int cap_task_setscheduler(struct task_struct *p)
{
	return cap_safe_nice(p);
}

/**
 * cap_task_ioprio - Detemine if I/O priority change is permitted
 * @p: The task to affect
 * @ioprio: The I/O priority to set
 *
 * Detemine if the requested I/O priority change is permitted for the specified
 * task, returning 0 if permission is granted, -ve if denied.
 */
int cap_task_setioprio(struct task_struct *p, int ioprio)
{
	return cap_safe_nice(p);
}

/**
 * cap_task_ioprio - Detemine if task priority change is permitted
 * @p: The task to affect
 * @nice: The nice value to set
 *
 * Detemine if the requested task priority change is permitted for the
 * specified task, returning 0 if permission is granted, -ve if denied.
 */
int cap_task_setnice(struct task_struct *p, int nice)
{
	return cap_safe_nice(p);
}

/*
 * Implement PR_CAPBSET_DROP.  Attempt to remove the specified capability from
 * the current task's bounding set.  Returns 0 on success, -ve on error.
 */
static int cap_prctl_drop(unsigned long cap)
{
	struct cred *new;

	if (!ns_capable(current_user_ns(), CAP_SETPCAP))
		return -EPERM;
	if (!cap_valid(cap))
		return -EINVAL;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;
	cap_lower(new->cap_bset, cap);
	return commit_creds(new);
}

/**
 * cap_task_prctl - Implement process control functions for this security module
 * @option: The process control function requested
 * @arg2, @arg3, @arg4, @arg5: The argument data for this function
 *
 * Allow process control functions (sys_prctl()) to alter capabilities; may
 * also deny access to other functions not otherwise implemented here.
 *
 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented
 * here, other -ve on error.  If -ENOSYS is returned, sys_prctl() and other LSM
 * modules will consider performing the function.
 */
int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
		   unsigned long arg4, unsigned long arg5)
{
	const struct cred *old = current_cred();
	struct cred *new;

	switch (option) {
	case PR_CAPBSET_READ:
		if (!cap_valid(arg2))
			return -EINVAL;
		return !!cap_raised(old->cap_bset, arg2);

	case PR_CAPBSET_DROP:
		return cap_prctl_drop(arg2);

	/*
	 * The next four prctl's remain to assist with transitioning a
	 * system from legacy UID=0 based privilege (when filesystem
	 * capabilities are not in use) to a system using filesystem
	 * capabilities only - as the POSIX.1e draft intended.
	 *
	 * Note:
	 *
	 *  PR_SET_SECUREBITS =
	 *      issecure_mask(SECURE_KEEP_CAPS_LOCKED)
	 *    | issecure_mask(SECURE_NOROOT)
	 *    | issecure_mask(SECURE_NOROOT_LOCKED)
	 *    | issecure_mask(SECURE_NO_SETUID_FIXUP)
	 *    | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
	 *
	 * will ensure that the current process and all of its
	 * children will be locked into a pure
	 * capability-based-privilege environment.
	 */
	case PR_SET_SECUREBITS:
		if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
		     & (old->securebits ^ arg2))			/*[1]*/
		    || ((old->securebits & SECURE_ALL_LOCKS & ~arg2))	/*[2]*/
		    || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))	/*[3]*/
		    || (cap_capable(current_cred(),
				    current_cred()->user_ns, CAP_SETPCAP,
				    SECURITY_CAP_AUDIT) != 0)		/*[4]*/
			/*
			 * [1] no changing of bits that are locked
			 * [2] no unlocking of locks
			 * [3] no setting of unsupported bits
			 * [4] doing anything requires privilege (go read about
			 *     the "sendmail capabilities bug")
			 */
		    )
			/* cannot change a locked bit */
			return -EPERM;

		new = prepare_creds();
		if (!new)
			return -ENOMEM;
		new->securebits = arg2;
		return commit_creds(new);

	case PR_GET_SECUREBITS:
		return old->securebits;

	case PR_GET_KEEPCAPS:
		return !!issecure(SECURE_KEEP_CAPS);

	case PR_SET_KEEPCAPS:
		if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
			return -EINVAL;
		if (issecure(SECURE_KEEP_CAPS_LOCKED))
			return -EPERM;

		new = prepare_creds();
		if (!new)
			return -ENOMEM;
		if (arg2)
			new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
		else
			new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
		return commit_creds(new);

	default:
		/* No functionality available - continue with default */
		return -ENOSYS;
	}
}

/**
 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
 * @mm: The VM space in which the new mapping is to be made
 * @pages: The size of the mapping
 *
 * Determine whether the allocation of a new virtual mapping by the current
 * task is permitted, returning 0 if permission is granted, -ve if not.
 */
int cap_vm_enough_memory(struct mm_struct *mm, long pages)
{
	int cap_sys_admin = 0;

	if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
			SECURITY_CAP_NOAUDIT) == 0)
		cap_sys_admin = 1;
	return __vm_enough_memory(mm, pages, cap_sys_admin);
}

/*
 * cap_mmap_addr - check if able to map given addr
 * @addr: address attempting to be mapped
 *
 * If the process is attempting to map memory below dac_mmap_min_addr they need
 * CAP_SYS_RAWIO.  The other parameters to this function are unused by the
 * capability security module.  Returns 0 if this mapping should be allowed
 * -EPERM if not.
 */
int cap_mmap_addr(unsigned long addr)
{
	int ret = 0;

	if (addr < dac_mmap_min_addr) {
		ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
				  SECURITY_CAP_AUDIT);
		/* set PF_SUPERPRIV if it turns out we allow the low mmap */
		if (ret == 0)
			current->flags |= PF_SUPERPRIV;
	}
	return ret;
}

int cap_mmap_file(struct file *file, unsigned long reqprot,
		  unsigned long prot, unsigned long flags)
{
	return 0;
}