1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * AppArmor security module
  4 *
  5 * This file contains AppArmor mediation of files
  6 *
  7 * Copyright (C) 1998-2008 Novell/SUSE
  8 * Copyright 2009-2010 Canonical Ltd.
 
 
 
 
 
  9 */
 10
 11#include <linux/tty.h>
 12#include <linux/fdtable.h>
 13#include <linux/file.h>
 14
 15#include "include/apparmor.h"
 16#include "include/audit.h"
 17#include "include/cred.h"
 18#include "include/file.h"
 19#include "include/match.h"
 20#include "include/net.h"
 21#include "include/path.h"
 22#include "include/policy.h"
 23#include "include/label.h"
 24
 25static u32 map_mask_to_chr_mask(u32 mask)
 26{
 27	u32 m = mask & PERMS_CHRS_MASK;
 28
 29	if (mask & AA_MAY_GETATTR)
 30		m |= MAY_READ;
 31	if (mask & (AA_MAY_SETATTR | AA_MAY_CHMOD | AA_MAY_CHOWN))
 32		m |= MAY_WRITE;
 33
 34	return m;
 35}
 36
 37/**
 38 * audit_file_mask - convert mask to permission string
 39 * @buffer: buffer to write string to (NOT NULL)
 40 * @mask: permission mask to convert
 41 */
 42static void audit_file_mask(struct audit_buffer *ab, u32 mask)
 43{
 44	char str[10];
 45
 46	aa_perm_mask_to_str(str, sizeof(str), aa_file_perm_chrs,
 47			    map_mask_to_chr_mask(mask));
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 48	audit_log_string(ab, str);
 49}
 50
 51/**
 52 * file_audit_cb - call back for file specific audit fields
 53 * @ab: audit_buffer  (NOT NULL)
 54 * @va: audit struct to audit values of  (NOT NULL)
 55 */
 56static void file_audit_cb(struct audit_buffer *ab, void *va)
 57{
 58	struct common_audit_data *sa = va;
 59	kuid_t fsuid = current_fsuid();
 60
 61	if (aad(sa)->request & AA_AUDIT_FILE_MASK) {
 62		audit_log_format(ab, " requested_mask=");
 63		audit_file_mask(ab, aad(sa)->request);
 64	}
 65	if (aad(sa)->denied & AA_AUDIT_FILE_MASK) {
 66		audit_log_format(ab, " denied_mask=");
 67		audit_file_mask(ab, aad(sa)->denied);
 68	}
 69	if (aad(sa)->request & AA_AUDIT_FILE_MASK) {
 70		audit_log_format(ab, " fsuid=%d",
 71				 from_kuid(&init_user_ns, fsuid));
 72		audit_log_format(ab, " ouid=%d",
 73				 from_kuid(&init_user_ns, aad(sa)->fs.ouid));
 74	}
 75
 76	if (aad(sa)->peer) {
 77		audit_log_format(ab, " target=");
 78		aa_label_xaudit(ab, labels_ns(aad(sa)->label), aad(sa)->peer,
 79				FLAG_VIEW_SUBNS, GFP_ATOMIC);
 80	} else if (aad(sa)->fs.target) {
 81		audit_log_format(ab, " target=");
 82		audit_log_untrustedstring(ab, aad(sa)->fs.target);
 83	}
 84}
 85
 86/**
 87 * aa_audit_file - handle the auditing of file operations
 88 * @profile: the profile being enforced  (NOT NULL)
 89 * @perms: the permissions computed for the request (NOT NULL)
 
 90 * @op: operation being mediated
 91 * @request: permissions requested
 92 * @name: name of object being mediated (MAYBE NULL)
 93 * @target: name of target (MAYBE NULL)
 94 * @tlabel: target label (MAY BE NULL)
 95 * @ouid: object uid
 96 * @info: extra information message (MAYBE NULL)
 97 * @error: 0 if operation allowed else failure error code
 98 *
 99 * Returns: %0 or error on failure
100 */
101int aa_audit_file(struct aa_profile *profile, struct aa_perms *perms,
102		  const char *op, u32 request, const char *name,
103		  const char *target, struct aa_label *tlabel,
104		  kuid_t ouid, const char *info, int error)
105{
106	int type = AUDIT_APPARMOR_AUTO;
107	DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_TASK, op);
 
 
 
 
 
 
 
 
 
 
108
109	sa.u.tsk = NULL;
110	aad(&sa)->request = request;
111	aad(&sa)->name = name;
112	aad(&sa)->fs.target = target;
113	aad(&sa)->peer = tlabel;
114	aad(&sa)->fs.ouid = ouid;
115	aad(&sa)->info = info;
116	aad(&sa)->error = error;
117	sa.u.tsk = NULL;
118
119	if (likely(!aad(&sa)->error)) {
120		u32 mask = perms->audit;
121
122		if (unlikely(AUDIT_MODE(profile) == AUDIT_ALL))
123			mask = 0xffff;
124
125		/* mask off perms that are not being force audited */
126		aad(&sa)->request &= mask;
127
128		if (likely(!aad(&sa)->request))
129			return 0;
130		type = AUDIT_APPARMOR_AUDIT;
131	} else {
132		/* only report permissions that were denied */
133		aad(&sa)->request = aad(&sa)->request & ~perms->allow;
134		AA_BUG(!aad(&sa)->request);
135
136		if (aad(&sa)->request & perms->kill)
137			type = AUDIT_APPARMOR_KILL;
138
139		/* quiet known rejects, assumes quiet and kill do not overlap */
140		if ((aad(&sa)->request & perms->quiet) &&
141		    AUDIT_MODE(profile) != AUDIT_NOQUIET &&
142		    AUDIT_MODE(profile) != AUDIT_ALL)
143			aad(&sa)->request &= ~perms->quiet;
144
145		if (!aad(&sa)->request)
146			return aad(&sa)->error;
147	}
148
149	aad(&sa)->denied = aad(&sa)->request & ~perms->allow;
150	return aa_audit(type, profile, &sa, file_audit_cb);
151}
152
153/**
154 * is_deleted - test if a file has been completely unlinked
155 * @dentry: dentry of file to test for deletion  (NOT NULL)
156 *
157 * Returns: %1 if deleted else %0
158 */
159static inline bool is_deleted(struct dentry *dentry)
160{
161	if (d_unlinked(dentry) && d_backing_inode(dentry)->i_nlink == 0)
162		return 1;
163	return 0;
164}
165
166static int path_name(const char *op, struct aa_label *label,
167		     const struct path *path, int flags, char *buffer,
168		     const char **name, struct path_cond *cond, u32 request)
169{
170	struct aa_profile *profile;
171	const char *info = NULL;
172	int error;
173
174	error = aa_path_name(path, flags, buffer, name, &info,
175			     labels_profile(label)->disconnected);
176	if (error) {
177		fn_for_each_confined(label, profile,
178			aa_audit_file(profile, &nullperms, op, request, *name,
179				      NULL, NULL, cond->uid, info, error));
180		return error;
181	}
182
183	return 0;
184}
185
186/**
187 * map_old_perms - map old file perms layout to the new layout
188 * @old: permission set in old mapping
189 *
190 * Returns: new permission mapping
191 */
192static u32 map_old_perms(u32 old)
193{
194	u32 new = old & 0xf;
195	if (old & MAY_READ)
196		new |= AA_MAY_GETATTR | AA_MAY_OPEN;
197	if (old & MAY_WRITE)
198		new |= AA_MAY_SETATTR | AA_MAY_CREATE | AA_MAY_DELETE |
199		       AA_MAY_CHMOD | AA_MAY_CHOWN | AA_MAY_OPEN;
200	if (old & 0x10)
201		new |= AA_MAY_LINK;
202	/* the old mapping lock and link_subset flags where overlaid
203	 * and use was determined by part of a pair that they were in
204	 */
205	if (old & 0x20)
206		new |= AA_MAY_LOCK | AA_LINK_SUBSET;
207	if (old & 0x40)	/* AA_EXEC_MMAP */
208		new |= AA_EXEC_MMAP;
209
210	return new;
211}
212
213/**
214 * aa_compute_fperms - convert dfa compressed perms to internal perms
215 * @dfa: dfa to compute perms for   (NOT NULL)
216 * @state: state in dfa
217 * @cond:  conditions to consider  (NOT NULL)
218 *
219 * TODO: convert from dfa + state to permission entry, do computation conversion
220 *       at load time.
221 *
222 * Returns: computed permission set
223 */
224struct aa_perms aa_compute_fperms(struct aa_dfa *dfa, unsigned int state,
225				  struct path_cond *cond)
226{
 
 
227	/* FIXME: change over to new dfa format
228	 * currently file perms are encoded in the dfa, new format
229	 * splits the permissions from the dfa.  This mapping can be
230	 * done at profile load
231	 */
232	struct aa_perms perms = { };
233
234	if (uid_eq(current_fsuid(), cond->uid)) {
235		perms.allow = map_old_perms(dfa_user_allow(dfa, state));
236		perms.audit = map_old_perms(dfa_user_audit(dfa, state));
237		perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
238		perms.xindex = dfa_user_xindex(dfa, state);
239	} else {
240		perms.allow = map_old_perms(dfa_other_allow(dfa, state));
241		perms.audit = map_old_perms(dfa_other_audit(dfa, state));
242		perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
243		perms.xindex = dfa_other_xindex(dfa, state);
244	}
245	perms.allow |= AA_MAY_GETATTR;
246
247	/* change_profile wasn't determined by ownership in old mapping */
248	if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
249		perms.allow |= AA_MAY_CHANGE_PROFILE;
250	if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
251		perms.allow |= AA_MAY_ONEXEC;
252
253	return perms;
254}
255
256/**
257 * aa_str_perms - find permission that match @name
258 * @dfa: to match against  (MAYBE NULL)
259 * @state: state to start matching in
260 * @name: string to match against dfa  (NOT NULL)
261 * @cond: conditions to consider for permission set computation  (NOT NULL)
262 * @perms: Returns - the permissions found when matching @name
263 *
264 * Returns: the final state in @dfa when beginning @start and walking @name
265 */
266unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
267			  const char *name, struct path_cond *cond,
268			  struct aa_perms *perms)
269{
270	unsigned int state;
 
 
 
 
 
271	state = aa_dfa_match(dfa, start, name);
272	*perms = aa_compute_fperms(dfa, state, cond);
273
274	return state;
275}
276
277int __aa_path_perm(const char *op, struct aa_profile *profile, const char *name,
278		   u32 request, struct path_cond *cond, int flags,
279		   struct aa_perms *perms)
280{
281	int e = 0;
282
283	if (profile_unconfined(profile))
284		return 0;
285	aa_str_perms(profile->file.dfa, profile->file.start, name, cond, perms);
286	if (request & ~perms->allow)
287		e = -EACCES;
288	return aa_audit_file(profile, perms, op, request, name, NULL, NULL,
289			     cond->uid, NULL, e);
290}
291
292
293static int profile_path_perm(const char *op, struct aa_profile *profile,
294			     const struct path *path, char *buffer, u32 request,
295			     struct path_cond *cond, int flags,
296			     struct aa_perms *perms)
297{
298	const char *name;
299	int error;
300
301	if (profile_unconfined(profile))
302		return 0;
303
304	error = path_name(op, &profile->label, path,
305			  flags | profile->path_flags, buffer, &name, cond,
306			  request);
307	if (error)
308		return error;
309	return __aa_path_perm(op, profile, name, request, cond, flags,
310			      perms);
311}
312
313/**
314 * aa_path_perm - do permissions check & audit for @path
315 * @op: operation being checked
316 * @label: profile being enforced  (NOT NULL)
317 * @path: path to check permissions of  (NOT NULL)
318 * @flags: any additional path flags beyond what the profile specifies
319 * @request: requested permissions
320 * @cond: conditional info for this request  (NOT NULL)
321 *
322 * Returns: %0 else error if access denied or other error
323 */
324int aa_path_perm(const char *op, struct aa_label *label,
325		 const struct path *path, int flags, u32 request,
326		 struct path_cond *cond)
327{
328	struct aa_perms perms = {};
329	struct aa_profile *profile;
330	char *buffer = NULL;
 
 
331	int error;
332
333	flags |= PATH_DELEGATE_DELETED | (S_ISDIR(cond->mode) ? PATH_IS_DIR :
334								0);
335	get_buffers(buffer);
336	error = fn_for_each_confined(label, profile,
337			profile_path_perm(op, profile, path, buffer, request,
338					  cond, flags, &perms));
339
340	put_buffers(buffer);
 
 
 
 
 
 
 
 
 
 
 
 
341
342	return error;
343}
344
345/**
346 * xindex_is_subset - helper for aa_path_link
347 * @link: link permission set
348 * @target: target permission set
349 *
350 * test target x permissions are equal OR a subset of link x permissions
351 * this is done as part of the subset test, where a hardlink must have
352 * a subset of permissions that the target has.
353 *
354 * Returns: %1 if subset else %0
355 */
356static inline bool xindex_is_subset(u32 link, u32 target)
357{
358	if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
359	    ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
360		return 0;
361
362	return 1;
363}
364
365static int profile_path_link(struct aa_profile *profile,
366			     const struct path *link, char *buffer,
367			     const struct path *target, char *buffer2,
368			     struct path_cond *cond)
369{
370	const char *lname, *tname = NULL;
371	struct aa_perms lperms = {}, perms;
372	const char *info = NULL;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
373	u32 request = AA_MAY_LINK;
374	unsigned int state;
375	int error;
376
377	error = path_name(OP_LINK, &profile->label, link, profile->path_flags,
378			  buffer, &lname, cond, AA_MAY_LINK);
 
 
 
379	if (error)
380		goto audit;
381
382	/* buffer2 freed below, tname is pointer in buffer2 */
383	error = path_name(OP_LINK, &profile->label, target, profile->path_flags,
384			  buffer2, &tname, cond, AA_MAY_LINK);
385	if (error)
386		goto audit;
387
388	error = -EACCES;
389	/* aa_str_perms - handles the case of the dfa being NULL */
390	state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
391			     cond, &lperms);
392
393	if (!(lperms.allow & AA_MAY_LINK))
394		goto audit;
395
396	/* test to see if target can be paired with link */
397	state = aa_dfa_null_transition(profile->file.dfa, state);
398	aa_str_perms(profile->file.dfa, state, tname, cond, &perms);
399
400	/* force audit/quiet masks for link are stored in the second entry
401	 * in the link pair.
402	 */
403	lperms.audit = perms.audit;
404	lperms.quiet = perms.quiet;
405	lperms.kill = perms.kill;
406
407	if (!(perms.allow & AA_MAY_LINK)) {
408		info = "target restricted";
409		lperms = perms;
410		goto audit;
411	}
412
413	/* done if link subset test is not required */
414	if (!(perms.allow & AA_LINK_SUBSET))
415		goto done_tests;
416
417	/* Do link perm subset test requiring allowed permission on link are
418	 * a subset of the allowed permissions on target.
419	 */
420	aa_str_perms(profile->file.dfa, profile->file.start, tname, cond,
421		     &perms);
422
423	/* AA_MAY_LINK is not considered in the subset test */
424	request = lperms.allow & ~AA_MAY_LINK;
425	lperms.allow &= perms.allow | AA_MAY_LINK;
426
427	request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
428	if (request & ~lperms.allow) {
429		goto audit;
430	} else if ((lperms.allow & MAY_EXEC) &&
431		   !xindex_is_subset(lperms.xindex, perms.xindex)) {
432		lperms.allow &= ~MAY_EXEC;
433		request |= MAY_EXEC;
434		info = "link not subset of target";
435		goto audit;
436	}
437
438done_tests:
439	error = 0;
440
441audit:
442	return aa_audit_file(profile, &lperms, OP_LINK, request, lname, tname,
443			     NULL, cond->uid, info, error);
444}
445
446/**
447 * aa_path_link - Handle hard link permission check
448 * @label: the label being enforced  (NOT NULL)
449 * @old_dentry: the target dentry  (NOT NULL)
450 * @new_dir: directory the new link will be created in  (NOT NULL)
451 * @new_dentry: the link being created  (NOT NULL)
452 *
453 * Handle the permission test for a link & target pair.  Permission
454 * is encoded as a pair where the link permission is determined
455 * first, and if allowed, the target is tested.  The target test
456 * is done from the point of the link match (not start of DFA)
457 * making the target permission dependent on the link permission match.
458 *
459 * The subset test if required forces that permissions granted
460 * on link are a subset of the permission granted to target.
461 *
462 * Returns: %0 if allowed else error
463 */
464int aa_path_link(struct aa_label *label, struct dentry *old_dentry,
465		 const struct path *new_dir, struct dentry *new_dentry)
466{
467	struct path link = { .mnt = new_dir->mnt, .dentry = new_dentry };
468	struct path target = { .mnt = new_dir->mnt, .dentry = old_dentry };
469	struct path_cond cond = {
470		d_backing_inode(old_dentry)->i_uid,
471		d_backing_inode(old_dentry)->i_mode
472	};
473	char *buffer = NULL, *buffer2 = NULL;
474	struct aa_profile *profile;
475	int error;
476
477	/* buffer freed below, lname is pointer in buffer */
478	get_buffers(buffer, buffer2);
479	error = fn_for_each_confined(label, profile,
480			profile_path_link(profile, &link, buffer, &target,
481					  buffer2, &cond));
482	put_buffers(buffer, buffer2);
483
484	return error;
485}
486
487static void update_file_ctx(struct aa_file_ctx *fctx, struct aa_label *label,
488			    u32 request)
489{
490	struct aa_label *l, *old;
491
492	/* update caching of label on file_ctx */
493	spin_lock(&fctx->lock);
494	old = rcu_dereference_protected(fctx->label,
495					lockdep_is_held(&fctx->lock));
496	l = aa_label_merge(old, label, GFP_ATOMIC);
497	if (l) {
498		if (l != old) {
499			rcu_assign_pointer(fctx->label, l);
500			aa_put_label(old);
501		} else
502			aa_put_label(l);
503		fctx->allow |= request;
504	}
505	spin_unlock(&fctx->lock);
506}
507
508static int __file_path_perm(const char *op, struct aa_label *label,
509			    struct aa_label *flabel, struct file *file,
510			    u32 request, u32 denied)
511{
512	struct aa_profile *profile;
513	struct aa_perms perms = {};
514	struct path_cond cond = {
515		.uid = file_inode(file)->i_uid,
516		.mode = file_inode(file)->i_mode
517	};
518	char *buffer;
519	int flags, error;
520
521	/* revalidation due to label out of date. No revocation at this time */
522	if (!denied && aa_label_is_subset(flabel, label))
523		/* TODO: check for revocation on stale profiles */
524		return 0;
525
526	flags = PATH_DELEGATE_DELETED | (S_ISDIR(cond.mode) ? PATH_IS_DIR : 0);
527	get_buffers(buffer);
528
529	/* check every profile in task label not in current cache */
530	error = fn_for_each_not_in_set(flabel, label, profile,
531			profile_path_perm(op, profile, &file->f_path, buffer,
532					  request, &cond, flags, &perms));
533	if (denied && !error) {
534		/*
535		 * check every profile in file label that was not tested
536		 * in the initial check above.
537		 *
538		 * TODO: cache full perms so this only happens because of
539		 * conditionals
540		 * TODO: don't audit here
541		 */
542		if (label == flabel)
543			error = fn_for_each(label, profile,
544				profile_path_perm(op, profile, &file->f_path,
545						  buffer, request, &cond, flags,
546						  &perms));
547		else
548			error = fn_for_each_not_in_set(label, flabel, profile,
549				profile_path_perm(op, profile, &file->f_path,
550						  buffer, request, &cond, flags,
551						  &perms));
552	}
553	if (!error)
554		update_file_ctx(file_ctx(file), label, request);
555
556	put_buffers(buffer);
557
558	return error;
559}
560
561static int __file_sock_perm(const char *op, struct aa_label *label,
562			    struct aa_label *flabel, struct file *file,
563			    u32 request, u32 denied)
564{
565	struct socket *sock = (struct socket *) file->private_data;
566	int error;
567
568	AA_BUG(!sock);
569
570	/* revalidation due to label out of date. No revocation at this time */
571	if (!denied && aa_label_is_subset(flabel, label))
572		return 0;
573
574	/* TODO: improve to skip profiles cached in flabel */
575	error = aa_sock_file_perm(label, op, request, sock);
576	if (denied) {
577		/* TODO: improve to skip profiles checked above */
578		/* check every profile in file label to is cached */
579		last_error(error, aa_sock_file_perm(flabel, op, request, sock));
580	}
581	if (!error)
582		update_file_ctx(file_ctx(file), label, request);
583
584	return error;
585}
586
587/**
588 * aa_file_perm - do permission revalidation check & audit for @file
589 * @op: operation being checked
590 * @label: label being enforced   (NOT NULL)
591 * @file: file to revalidate access permissions on  (NOT NULL)
592 * @request: requested permissions
593 *
594 * Returns: %0 if access allowed else error
595 */
596int aa_file_perm(const char *op, struct aa_label *label, struct file *file,
597		 u32 request)
598{
599	struct aa_file_ctx *fctx;
600	struct aa_label *flabel;
601	u32 denied;
602	int error = 0;
603
604	AA_BUG(!label);
605	AA_BUG(!file);
606
607	fctx = file_ctx(file);
608
609	rcu_read_lock();
610	flabel  = rcu_dereference(fctx->label);
611	AA_BUG(!flabel);
612
613	/* revalidate access, if task is unconfined, or the cached cred
614	 * doesn't match or if the request is for more permissions than
615	 * was granted.
616	 *
617	 * Note: the test for !unconfined(flabel) is to handle file
618	 *       delegation from unconfined tasks
619	 */
620	denied = request & ~fctx->allow;
621	if (unconfined(label) || unconfined(flabel) ||
622	    (!denied && aa_label_is_subset(flabel, label)))
623		goto done;
624
625	/* TODO: label cross check */
626
627	if (file->f_path.mnt && path_mediated_fs(file->f_path.dentry))
628		error = __file_path_perm(op, label, flabel, file, request,
629					 denied);
630
631	else if (S_ISSOCK(file_inode(file)->i_mode))
632		error = __file_sock_perm(op, label, flabel, file, request,
633					 denied);
634done:
635	rcu_read_unlock();
636
637	return error;
638}
639
640static void revalidate_tty(struct aa_label *label)
641{
642	struct tty_struct *tty;
643	int drop_tty = 0;
644
645	tty = get_current_tty();
646	if (!tty)
647		return;
648
649	spin_lock(&tty->files_lock);
650	if (!list_empty(&tty->tty_files)) {
651		struct tty_file_private *file_priv;
652		struct file *file;
653		/* TODO: Revalidate access to controlling tty. */
654		file_priv = list_first_entry(&tty->tty_files,
655					     struct tty_file_private, list);
656		file = file_priv->file;
657
658		if (aa_file_perm(OP_INHERIT, label, file, MAY_READ | MAY_WRITE))
659			drop_tty = 1;
660	}
661	spin_unlock(&tty->files_lock);
662	tty_kref_put(tty);
663
664	if (drop_tty)
665		no_tty();
666}
667
668static int match_file(const void *p, struct file *file, unsigned int fd)
669{
670	struct aa_label *label = (struct aa_label *)p;
671
672	if (aa_file_perm(OP_INHERIT, label, file, aa_map_file_to_perms(file)))
673		return fd + 1;
674	return 0;
675}
676
677
678/* based on selinux's flush_unauthorized_files */
679void aa_inherit_files(const struct cred *cred, struct files_struct *files)
680{
681	struct aa_label *label = aa_get_newest_cred_label(cred);
682	struct file *devnull = NULL;
683	unsigned int n;
684
685	revalidate_tty(label);
686
687	/* Revalidate access to inherited open files. */
688	n = iterate_fd(files, 0, match_file, label);
689	if (!n) /* none found? */
690		goto out;
691
692	devnull = dentry_open(&aa_null, O_RDWR, cred);
693	if (IS_ERR(devnull))
694		devnull = NULL;
695	/* replace all the matching ones with this */
696	do {
697		replace_fd(n - 1, devnull, 0);
698	} while ((n = iterate_fd(files, n, match_file, label)) != 0);
699	if (devnull)
700		fput(devnull);
701out:
702	aa_put_label(label);
703}