1/*
  2 * AppArmor security module
  3 *
  4 * This file contains AppArmor mediation of files
  5 *
  6 * Copyright (C) 1998-2008 Novell/SUSE
  7 * Copyright 2009-2010 Canonical Ltd.
  8 *
  9 * This program is free software; you can redistribute it and/or
 10 * modify it under the terms of the GNU General Public License as
 11 * published by the Free Software Foundation, version 2 of the
 12 * License.
 13 */
 14
 15#include <linux/tty.h>
 16#include <linux/fdtable.h>
 17#include <linux/file.h>
 18
 19#include "include/apparmor.h"
 20#include "include/audit.h"
 21#include "include/cred.h"
 22#include "include/file.h"
 23#include "include/match.h"
 24#include "include/net.h"
 25#include "include/path.h"
 26#include "include/policy.h"
 27#include "include/label.h"
 28
 29static u32 map_mask_to_chr_mask(u32 mask)
 30{
 31	u32 m = mask & PERMS_CHRS_MASK;
 32
 33	if (mask & AA_MAY_GETATTR)
 34		m |= MAY_READ;
 35	if (mask & (AA_MAY_SETATTR | AA_MAY_CHMOD | AA_MAY_CHOWN))
 36		m |= MAY_WRITE;
 37
 38	return m;
 39}
 40
 41/**
 42 * audit_file_mask - convert mask to permission string
 43 * @buffer: buffer to write string to (NOT NULL)
 44 * @mask: permission mask to convert
 45 */
 46static void audit_file_mask(struct audit_buffer *ab, u32 mask)
 47{
 48	char str[10];
 49
 50	aa_perm_mask_to_str(str, aa_file_perm_chrs, map_mask_to_chr_mask(mask));
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 51	audit_log_string(ab, str);
 52}
 53
 54/**
 55 * file_audit_cb - call back for file specific audit fields
 56 * @ab: audit_buffer  (NOT NULL)
 57 * @va: audit struct to audit values of  (NOT NULL)
 58 */
 59static void file_audit_cb(struct audit_buffer *ab, void *va)
 60{
 61	struct common_audit_data *sa = va;
 62	kuid_t fsuid = current_fsuid();
 63
 64	if (aad(sa)->request & AA_AUDIT_FILE_MASK) {
 65		audit_log_format(ab, " requested_mask=");
 66		audit_file_mask(ab, aad(sa)->request);
 67	}
 68	if (aad(sa)->denied & AA_AUDIT_FILE_MASK) {
 69		audit_log_format(ab, " denied_mask=");
 70		audit_file_mask(ab, aad(sa)->denied);
 71	}
 72	if (aad(sa)->request & AA_AUDIT_FILE_MASK) {
 73		audit_log_format(ab, " fsuid=%d",
 74				 from_kuid(&init_user_ns, fsuid));
 75		audit_log_format(ab, " ouid=%d",
 76				 from_kuid(&init_user_ns, aad(sa)->fs.ouid));
 77	}
 78
 79	if (aad(sa)->peer) {
 80		audit_log_format(ab, " target=");
 81		aa_label_xaudit(ab, labels_ns(aad(sa)->label), aad(sa)->peer,
 82				FLAG_VIEW_SUBNS, GFP_ATOMIC);
 83	} else if (aad(sa)->fs.target) {
 84		audit_log_format(ab, " target=");
 85		audit_log_untrustedstring(ab, aad(sa)->fs.target);
 86	}
 87}
 88
 89/**
 90 * aa_audit_file - handle the auditing of file operations
 91 * @profile: the profile being enforced  (NOT NULL)
 92 * @perms: the permissions computed for the request (NOT NULL)
 
 93 * @op: operation being mediated
 94 * @request: permissions requested
 95 * @name: name of object being mediated (MAYBE NULL)
 96 * @target: name of target (MAYBE NULL)
 97 * @tlabel: target label (MAY BE NULL)
 98 * @ouid: object uid
 99 * @info: extra information message (MAYBE NULL)
100 * @error: 0 if operation allowed else failure error code
101 *
102 * Returns: %0 or error on failure
103 */
104int aa_audit_file(struct aa_profile *profile, struct aa_perms *perms,
105		  const char *op, u32 request, const char *name,
106		  const char *target, struct aa_label *tlabel,
107		  kuid_t ouid, const char *info, int error)
108{
109	int type = AUDIT_APPARMOR_AUTO;
110	DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_TASK, op);
111
112	sa.u.tsk = NULL;
113	aad(&sa)->request = request;
114	aad(&sa)->name = name;
115	aad(&sa)->fs.target = target;
116	aad(&sa)->peer = tlabel;
117	aad(&sa)->fs.ouid = ouid;
118	aad(&sa)->info = info;
119	aad(&sa)->error = error;
120	sa.u.tsk = NULL;
121
122	if (likely(!aad(&sa)->error)) {
123		u32 mask = perms->audit;
124
125		if (unlikely(AUDIT_MODE(profile) == AUDIT_ALL))
126			mask = 0xffff;
127
128		/* mask off perms that are not being force audited */
129		aad(&sa)->request &= mask;
130
131		if (likely(!aad(&sa)->request))
132			return 0;
133		type = AUDIT_APPARMOR_AUDIT;
134	} else {
135		/* only report permissions that were denied */
136		aad(&sa)->request = aad(&sa)->request & ~perms->allow;
137		AA_BUG(!aad(&sa)->request);
138
139		if (aad(&sa)->request & perms->kill)
140			type = AUDIT_APPARMOR_KILL;
141
142		/* quiet known rejects, assumes quiet and kill do not overlap */
143		if ((aad(&sa)->request & perms->quiet) &&
144		    AUDIT_MODE(profile) != AUDIT_NOQUIET &&
145		    AUDIT_MODE(profile) != AUDIT_ALL)
146			aad(&sa)->request &= ~perms->quiet;
147
148		if (!aad(&sa)->request)
149			return aad(&sa)->error;
150	}
151
152	aad(&sa)->denied = aad(&sa)->request & ~perms->allow;
153	return aa_audit(type, profile, &sa, file_audit_cb);
154}
155
156/**
157 * is_deleted - test if a file has been completely unlinked
158 * @dentry: dentry of file to test for deletion  (NOT NULL)
159 *
160 * Returns: %1 if deleted else %0
161 */
162static inline bool is_deleted(struct dentry *dentry)
163{
164	if (d_unlinked(dentry) && d_backing_inode(dentry)->i_nlink == 0)
165		return 1;
166	return 0;
167}
168
169static int path_name(const char *op, struct aa_label *label,
170		     const struct path *path, int flags, char *buffer,
171		     const char **name, struct path_cond *cond, u32 request)
172{
173	struct aa_profile *profile;
174	const char *info = NULL;
175	int error;
176
177	error = aa_path_name(path, flags, buffer, name, &info,
178			     labels_profile(label)->disconnected);
179	if (error) {
180		fn_for_each_confined(label, profile,
181			aa_audit_file(profile, &nullperms, op, request, *name,
182				      NULL, NULL, cond->uid, info, error));
183		return error;
184	}
185
186	return 0;
 
187}
188
189/**
190 * map_old_perms - map old file perms layout to the new layout
191 * @old: permission set in old mapping
192 *
193 * Returns: new permission mapping
194 */
195static u32 map_old_perms(u32 old)
196{
197	u32 new = old & 0xf;
198	if (old & MAY_READ)
199		new |= AA_MAY_GETATTR | AA_MAY_OPEN;
200	if (old & MAY_WRITE)
201		new |= AA_MAY_SETATTR | AA_MAY_CREATE | AA_MAY_DELETE |
202		       AA_MAY_CHMOD | AA_MAY_CHOWN | AA_MAY_OPEN;
203	if (old & 0x10)
204		new |= AA_MAY_LINK;
205	/* the old mapping lock and link_subset flags where overlaid
206	 * and use was determined by part of a pair that they were in
207	 */
208	if (old & 0x20)
209		new |= AA_MAY_LOCK | AA_LINK_SUBSET;
210	if (old & 0x40)	/* AA_EXEC_MMAP */
211		new |= AA_EXEC_MMAP;
212
 
 
213	return new;
214}
215
216/**
217 * aa_compute_fperms - convert dfa compressed perms to internal perms
218 * @dfa: dfa to compute perms for   (NOT NULL)
219 * @state: state in dfa
220 * @cond:  conditions to consider  (NOT NULL)
221 *
222 * TODO: convert from dfa + state to permission entry, do computation conversion
223 *       at load time.
224 *
225 * Returns: computed permission set
226 */
227struct aa_perms aa_compute_fperms(struct aa_dfa *dfa, unsigned int state,
228				  struct path_cond *cond)
229{
 
 
230	/* FIXME: change over to new dfa format
231	 * currently file perms are encoded in the dfa, new format
232	 * splits the permissions from the dfa.  This mapping can be
233	 * done at profile load
234	 */
235	struct aa_perms perms = { };
236
237	if (uid_eq(current_fsuid(), cond->uid)) {
238		perms.allow = map_old_perms(dfa_user_allow(dfa, state));
239		perms.audit = map_old_perms(dfa_user_audit(dfa, state));
240		perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
241		perms.xindex = dfa_user_xindex(dfa, state);
242	} else {
243		perms.allow = map_old_perms(dfa_other_allow(dfa, state));
244		perms.audit = map_old_perms(dfa_other_audit(dfa, state));
245		perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
246		perms.xindex = dfa_other_xindex(dfa, state);
247	}
248	perms.allow |= AA_MAY_GETATTR;
249
250	/* change_profile wasn't determined by ownership in old mapping */
251	if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
252		perms.allow |= AA_MAY_CHANGE_PROFILE;
253	if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
254		perms.allow |= AA_MAY_ONEXEC;
255
256	return perms;
257}
258
259/**
260 * aa_str_perms - find permission that match @name
261 * @dfa: to match against  (MAYBE NULL)
262 * @state: state to start matching in
263 * @name: string to match against dfa  (NOT NULL)
264 * @cond: conditions to consider for permission set computation  (NOT NULL)
265 * @perms: Returns - the permissions found when matching @name
266 *
267 * Returns: the final state in @dfa when beginning @start and walking @name
268 */
269unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
270			  const char *name, struct path_cond *cond,
271			  struct aa_perms *perms)
272{
273	unsigned int state;
 
 
 
 
 
274	state = aa_dfa_match(dfa, start, name);
275	*perms = aa_compute_fperms(dfa, state, cond);
276
277	return state;
278}
279
280int __aa_path_perm(const char *op, struct aa_profile *profile, const char *name,
281		   u32 request, struct path_cond *cond, int flags,
282		   struct aa_perms *perms)
283{
284	int e = 0;
285
286	if (profile_unconfined(profile))
287		return 0;
288	aa_str_perms(profile->file.dfa, profile->file.start, name, cond, perms);
289	if (request & ~perms->allow)
290		e = -EACCES;
291	return aa_audit_file(profile, perms, op, request, name, NULL, NULL,
292			     cond->uid, NULL, e);
293}
294
295
296static int profile_path_perm(const char *op, struct aa_profile *profile,
297			     const struct path *path, char *buffer, u32 request,
298			     struct path_cond *cond, int flags,
299			     struct aa_perms *perms)
300{
301	const char *name;
302	int error;
303
304	if (profile_unconfined(profile))
305		return 0;
306
307	error = path_name(op, &profile->label, path,
308			  flags | profile->path_flags, buffer, &name, cond,
309			  request);
310	if (error)
311		return error;
312	return __aa_path_perm(op, profile, name, request, cond, flags,
313			      perms);
314}
315
316/**
317 * aa_path_perm - do permissions check & audit for @path
318 * @op: operation being checked
319 * @label: profile being enforced  (NOT NULL)
320 * @path: path to check permissions of  (NOT NULL)
321 * @flags: any additional path flags beyond what the profile specifies
322 * @request: requested permissions
323 * @cond: conditional info for this request  (NOT NULL)
324 *
325 * Returns: %0 else error if access denied or other error
326 */
327int aa_path_perm(const char *op, struct aa_label *label,
328		 const struct path *path, int flags, u32 request,
329		 struct path_cond *cond)
330{
331	struct aa_perms perms = {};
332	struct aa_profile *profile;
333	char *buffer = NULL;
 
 
334	int error;
335
336	flags |= PATH_DELEGATE_DELETED | (S_ISDIR(cond->mode) ? PATH_IS_DIR :
337								0);
338	get_buffers(buffer);
339	error = fn_for_each_confined(label, profile,
340			profile_path_perm(op, profile, path, buffer, request,
341					  cond, flags, &perms));
342
343	put_buffers(buffer);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
344
345	return error;
346}
347
348/**
349 * xindex_is_subset - helper for aa_path_link
350 * @link: link permission set
351 * @target: target permission set
352 *
353 * test target x permissions are equal OR a subset of link x permissions
354 * this is done as part of the subset test, where a hardlink must have
355 * a subset of permissions that the target has.
356 *
357 * Returns: %1 if subset else %0
358 */
359static inline bool xindex_is_subset(u32 link, u32 target)
360{
361	if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
362	    ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
363		return 0;
364
365	return 1;
366}
367
368static int profile_path_link(struct aa_profile *profile,
369			     const struct path *link, char *buffer,
370			     const struct path *target, char *buffer2,
371			     struct path_cond *cond)
372{
373	const char *lname, *tname = NULL;
374	struct aa_perms lperms = {}, perms;
375	const char *info = NULL;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
376	u32 request = AA_MAY_LINK;
377	unsigned int state;
378	int error;
379
380	error = path_name(OP_LINK, &profile->label, link, profile->path_flags,
381			  buffer, &lname, cond, AA_MAY_LINK);
 
 
382	if (error)
383		goto audit;
384
385	/* buffer2 freed below, tname is pointer in buffer2 */
386	error = path_name(OP_LINK, &profile->label, target, profile->path_flags,
387			  buffer2, &tname, cond, AA_MAY_LINK);
388	if (error)
389		goto audit;
390
391	error = -EACCES;
392	/* aa_str_perms - handles the case of the dfa being NULL */
393	state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
394			     cond, &lperms);
395
396	if (!(lperms.allow & AA_MAY_LINK))
397		goto audit;
398
399	/* test to see if target can be paired with link */
400	state = aa_dfa_null_transition(profile->file.dfa, state);
401	aa_str_perms(profile->file.dfa, state, tname, cond, &perms);
402
403	/* force audit/quiet masks for link are stored in the second entry
404	 * in the link pair.
405	 */
406	lperms.audit = perms.audit;
407	lperms.quiet = perms.quiet;
408	lperms.kill = perms.kill;
409
410	if (!(perms.allow & AA_MAY_LINK)) {
411		info = "target restricted";
412		lperms = perms;
413		goto audit;
414	}
415
416	/* done if link subset test is not required */
417	if (!(perms.allow & AA_LINK_SUBSET))
418		goto done_tests;
419
420	/* Do link perm subset test requiring allowed permission on link are
421	 * a subset of the allowed permissions on target.
422	 */
423	aa_str_perms(profile->file.dfa, profile->file.start, tname, cond,
424		     &perms);
425
426	/* AA_MAY_LINK is not considered in the subset test */
427	request = lperms.allow & ~AA_MAY_LINK;
428	lperms.allow &= perms.allow | AA_MAY_LINK;
429
430	request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
431	if (request & ~lperms.allow) {
432		goto audit;
433	} else if ((lperms.allow & MAY_EXEC) &&
434		   !xindex_is_subset(lperms.xindex, perms.xindex)) {
435		lperms.allow &= ~MAY_EXEC;
436		request |= MAY_EXEC;
437		info = "link not subset of target";
438		goto audit;
439	}
440
441done_tests:
442	error = 0;
443
444audit:
445	return aa_audit_file(profile, &lperms, OP_LINK, request, lname, tname,
446			     NULL, cond->uid, info, error);
447}
448
449/**
450 * aa_path_link - Handle hard link permission check
451 * @label: the label being enforced  (NOT NULL)
452 * @old_dentry: the target dentry  (NOT NULL)
453 * @new_dir: directory the new link will be created in  (NOT NULL)
454 * @new_dentry: the link being created  (NOT NULL)
455 *
456 * Handle the permission test for a link & target pair.  Permission
457 * is encoded as a pair where the link permission is determined
458 * first, and if allowed, the target is tested.  The target test
459 * is done from the point of the link match (not start of DFA)
460 * making the target permission dependent on the link permission match.
461 *
462 * The subset test if required forces that permissions granted
463 * on link are a subset of the permission granted to target.
464 *
465 * Returns: %0 if allowed else error
466 */
467int aa_path_link(struct aa_label *label, struct dentry *old_dentry,
468		 const struct path *new_dir, struct dentry *new_dentry)
469{
470	struct path link = { .mnt = new_dir->mnt, .dentry = new_dentry };
471	struct path target = { .mnt = new_dir->mnt, .dentry = old_dentry };
472	struct path_cond cond = {
473		d_backing_inode(old_dentry)->i_uid,
474		d_backing_inode(old_dentry)->i_mode
475	};
476	char *buffer = NULL, *buffer2 = NULL;
477	struct aa_profile *profile;
478	int error;
479
480	/* buffer freed below, lname is pointer in buffer */
481	get_buffers(buffer, buffer2);
482	error = fn_for_each_confined(label, profile,
483			profile_path_link(profile, &link, buffer, &target,
484					  buffer2, &cond));
485	put_buffers(buffer, buffer2);
486
487	return error;
488}
489
490static void update_file_ctx(struct aa_file_ctx *fctx, struct aa_label *label,
491			    u32 request)
492{
493	struct aa_label *l, *old;
494
495	/* update caching of label on file_ctx */
496	spin_lock(&fctx->lock);
497	old = rcu_dereference_protected(fctx->label,
498					spin_is_locked(&fctx->lock));
499	l = aa_label_merge(old, label, GFP_ATOMIC);
500	if (l) {
501		if (l != old) {
502			rcu_assign_pointer(fctx->label, l);
503			aa_put_label(old);
504		} else
505			aa_put_label(l);
506		fctx->allow |= request;
507	}
508	spin_unlock(&fctx->lock);
509}
510
511static int __file_path_perm(const char *op, struct aa_label *label,
512			    struct aa_label *flabel, struct file *file,
513			    u32 request, u32 denied)
514{
515	struct aa_profile *profile;
516	struct aa_perms perms = {};
517	struct path_cond cond = {
518		.uid = file_inode(file)->i_uid,
519		.mode = file_inode(file)->i_mode
520	};
521	char *buffer;
522	int flags, error;
523
524	/* revalidation due to label out of date. No revocation at this time */
525	if (!denied && aa_label_is_subset(flabel, label))
526		/* TODO: check for revocation on stale profiles */
527		return 0;
528
529	flags = PATH_DELEGATE_DELETED | (S_ISDIR(cond.mode) ? PATH_IS_DIR : 0);
530	get_buffers(buffer);
531
532	/* check every profile in task label not in current cache */
533	error = fn_for_each_not_in_set(flabel, label, profile,
534			profile_path_perm(op, profile, &file->f_path, buffer,
535					  request, &cond, flags, &perms));
536	if (denied && !error) {
537		/*
538		 * check every profile in file label that was not tested
539		 * in the initial check above.
540		 *
541		 * TODO: cache full perms so this only happens because of
542		 * conditionals
543		 * TODO: don't audit here
544		 */
545		if (label == flabel)
546			error = fn_for_each(label, profile,
547				profile_path_perm(op, profile, &file->f_path,
548						  buffer, request, &cond, flags,
549						  &perms));
550		else
551			error = fn_for_each_not_in_set(label, flabel, profile,
552				profile_path_perm(op, profile, &file->f_path,
553						  buffer, request, &cond, flags,
554						  &perms));
555	}
556	if (!error)
557		update_file_ctx(file_ctx(file), label, request);
558
559	put_buffers(buffer);
560
561	return error;
562}
563
564static int __file_sock_perm(const char *op, struct aa_label *label,
565			    struct aa_label *flabel, struct file *file,
566			    u32 request, u32 denied)
567{
568	struct socket *sock = (struct socket *) file->private_data;
569	int error;
570
571	AA_BUG(!sock);
572
573	/* revalidation due to label out of date. No revocation at this time */
574	if (!denied && aa_label_is_subset(flabel, label))
575		return 0;
576
577	/* TODO: improve to skip profiles cached in flabel */
578	error = aa_sock_file_perm(label, op, request, sock);
579	if (denied) {
580		/* TODO: improve to skip profiles checked above */
581		/* check every profile in file label to is cached */
582		last_error(error, aa_sock_file_perm(flabel, op, request, sock));
583	}
584	if (!error)
585		update_file_ctx(file_ctx(file), label, request);
586
587	return error;
588}
589
590/**
591 * aa_file_perm - do permission revalidation check & audit for @file
592 * @op: operation being checked
593 * @label: label being enforced   (NOT NULL)
594 * @file: file to revalidate access permissions on  (NOT NULL)
595 * @request: requested permissions
596 *
597 * Returns: %0 if access allowed else error
598 */
599int aa_file_perm(const char *op, struct aa_label *label, struct file *file,
600		 u32 request)
601{
602	struct aa_file_ctx *fctx;
603	struct aa_label *flabel;
604	u32 denied;
605	int error = 0;
606
607	AA_BUG(!label);
608	AA_BUG(!file);
609
610	fctx = file_ctx(file);
611
612	rcu_read_lock();
613	flabel  = rcu_dereference(fctx->label);
614	AA_BUG(!flabel);
615
616	/* revalidate access, if task is unconfined, or the cached cred
617	 * doesn't match or if the request is for more permissions than
618	 * was granted.
619	 *
620	 * Note: the test for !unconfined(flabel) is to handle file
621	 *       delegation from unconfined tasks
622	 */
623	denied = request & ~fctx->allow;
624	if (unconfined(label) || unconfined(flabel) ||
625	    (!denied && aa_label_is_subset(flabel, label)))
626		goto done;
627
628	/* TODO: label cross check */
629
630	if (file->f_path.mnt && path_mediated_fs(file->f_path.dentry))
631		error = __file_path_perm(op, label, flabel, file, request,
632					 denied);
633
634	else if (S_ISSOCK(file_inode(file)->i_mode))
635		error = __file_sock_perm(op, label, flabel, file, request,
636					 denied);
637done:
638	rcu_read_unlock();
639
640	return error;
641}
642
643static void revalidate_tty(struct aa_label *label)
644{
645	struct tty_struct *tty;
646	int drop_tty = 0;
647
648	tty = get_current_tty();
649	if (!tty)
650		return;
651
652	spin_lock(&tty->files_lock);
653	if (!list_empty(&tty->tty_files)) {
654		struct tty_file_private *file_priv;
655		struct file *file;
656		/* TODO: Revalidate access to controlling tty. */
657		file_priv = list_first_entry(&tty->tty_files,
658					     struct tty_file_private, list);
659		file = file_priv->file;
660
661		if (aa_file_perm(OP_INHERIT, label, file, MAY_READ | MAY_WRITE))
662			drop_tty = 1;
663	}
664	spin_unlock(&tty->files_lock);
665	tty_kref_put(tty);
666
667	if (drop_tty)
668		no_tty();
669}
670
671static int match_file(const void *p, struct file *file, unsigned int fd)
672{
673	struct aa_label *label = (struct aa_label *)p;
674
675	if (aa_file_perm(OP_INHERIT, label, file, aa_map_file_to_perms(file)))
676		return fd + 1;
677	return 0;
678}
679
680
681/* based on selinux's flush_unauthorized_files */
682void aa_inherit_files(const struct cred *cred, struct files_struct *files)
683{
684	struct aa_label *label = aa_get_newest_cred_label(cred);
685	struct file *devnull = NULL;
686	unsigned int n;
687
688	revalidate_tty(label);
689
690	/* Revalidate access to inherited open files. */
691	n = iterate_fd(files, 0, match_file, label);
692	if (!n) /* none found? */
693		goto out;
694
695	devnull = dentry_open(&aa_null, O_RDWR, cred);
696	if (IS_ERR(devnull))
697		devnull = NULL;
698	/* replace all the matching ones with this */
699	do {
700		replace_fd(n - 1, devnull, 0);
701	} while ((n = iterate_fd(files, n, match_file, label)) != 0);
702	if (devnull)
703		fput(devnull);
704out:
705	aa_put_label(label);
706}