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Linux/security/apparmor/file.c

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  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 
 25 static 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  */
 42 static 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  */
 56 static 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  */
101 int 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  */
159 static 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 
166 static 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  */
192 static 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  */
224 struct 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  */
266 unsigned 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 
277 int __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 
293 static 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  */
324 int 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  */
356 static 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 
365 static 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 
438 done_tests:
439         error = 0;
440 
441 audit:
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  */
464 int 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 
487 static 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 
508 static 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 
561 static 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  */
596 int 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);
634 done:
635         rcu_read_unlock();
636 
637         return error;
638 }
639 
640 static 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 
668 static 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 */
679 void 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);
701 out:
702         aa_put_label(label);
703 }
704 

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