security/apparmor/file.c

   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 "include/apparmor.h"
  16 #include "include/audit.h"
  17 #include "include/file.h"
  18 #include "include/match.h"
  19 #include "include/path.h"
  20 #include "include/policy.h"
  21
  22 struct file_perms nullperms;
  23
  24
  25 /**
  26  * audit_file_mask - convert mask to permission string
  27  * @buffer: buffer to write string to (NOT NULL)
  28  * @mask: permission mask to convert
  29  */
  30 static void audit_file_mask(struct audit_buffer *ab, u32 mask)
  31 {
  32         char str[10];
  33
  34         char *m = str;
  35
  36         if (mask & AA_EXEC_MMAP)
  37                 *m++ = 'm';
  38         if (mask & (MAY_READ | AA_MAY_META_READ))
  39                 *m++ = 'r';
  40         if (mask & (MAY_WRITE | AA_MAY_META_WRITE | AA_MAY_CHMOD |
  41                     AA_MAY_CHOWN))
  42                 *m++ = 'w';
  43         else if (mask & MAY_APPEND)
  44                 *m++ = 'a';
  45         if (mask & AA_MAY_CREATE)
  46                 *m++ = 'c';
  47         if (mask & AA_MAY_DELETE)
  48                 *m++ = 'd';
  49         if (mask & AA_MAY_LINK)
  50                 *m++ = 'l';
  51         if (mask & AA_MAY_LOCK)
  52                 *m++ = 'k';
  53         if (mask & MAY_EXEC)
  54                 *m++ = 'x';
  55         *m = '\0';
  56
  57         audit_log_string(ab, str);
  58 }
  59
  60 /**
  61  * file_audit_cb - call back for file specific audit fields
  62  * @ab: audit_buffer  (NOT NULL)
  63  * @va: audit struct to audit values of  (NOT NULL)
  64  */
  65 static void file_audit_cb(struct audit_buffer *ab, void *va)
  66 {
  67         struct common_audit_data *sa = va;
  68         kuid_t fsuid = current_fsuid();
  69
  70         if (aad(sa)->fs.request & AA_AUDIT_FILE_MASK) {
  71                 audit_log_format(ab, " requested_mask=");
  72                 audit_file_mask(ab, aad(sa)->fs.request);
  73         }
  74         if (aad(sa)->fs.denied & AA_AUDIT_FILE_MASK) {
  75                 audit_log_format(ab, " denied_mask=");
  76                 audit_file_mask(ab, aad(sa)->fs.denied);
  77         }
  78         if (aad(sa)->fs.request & AA_AUDIT_FILE_MASK) {
  79                 audit_log_format(ab, " fsuid=%d",
  80                                  from_kuid(&init_user_ns, fsuid));
  81                 audit_log_format(ab, " ouid=%d",
  82                                  from_kuid(&init_user_ns, aad(sa)->fs.ouid));
  83         }
  84
  85         if (aad(sa)->fs.target) {
  86                 audit_log_format(ab, " target=");
  87                 audit_log_untrustedstring(ab, aad(sa)->fs.target);
  88         }
  89 }
  90
  91 /**
  92  * aa_audit_file - handle the auditing of file operations
  93  * @profile: the profile being enforced  (NOT NULL)
  94  * @perms: the permissions computed for the request (NOT NULL)
  95  * @gfp: allocation flags
  96  * @op: operation being mediated
  97  * @request: permissions requested
  98  * @name: name of object being mediated (MAYBE NULL)
  99  * @target: name of target (MAYBE NULL)
 100  * @ouid: object uid
 101  * @info: extra information message (MAYBE NULL)
 102  * @error: 0 if operation allowed else failure error code
 103  *
 104  * Returns: %0 or error on failure
 105  */
 106 int aa_audit_file(struct aa_profile *profile, struct file_perms *perms,
 107                   const char *op, u32 request, const char *name,
 108                   const char *target, kuid_t ouid, const char *info, int error)
 109 {
 110         int type = AUDIT_APPARMOR_AUTO;
 111         DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_TASK, op);
 112
 113         sa.u.tsk = NULL;
 114         aad(&sa)->fs.request = request;
 115         aad(&sa)->name = name;
 116         aad(&sa)->fs.target = target;
 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)->fs.request &= mask;
 130
 131                 if (likely(!aad(&sa)->fs.request))
 132                         return 0;
 133                 type = AUDIT_APPARMOR_AUDIT;
 134         } else {
 135                 /* only report permissions that were denied */
 136                 aad(&sa)->fs.request = aad(&sa)->fs.request & ~perms->allow;
 137                 AA_BUG(!aad(&sa)->fs.request);
 138
 139                 if (aad(&sa)->fs.request & perms->kill)
 140                         type = AUDIT_APPARMOR_KILL;
 141
 142                 /* quiet known rejects, assumes quiet and kill do not overlap */
 143                 if ((aad(&sa)->fs.request & perms->quiet) &&
 144                     AUDIT_MODE(profile) != AUDIT_NOQUIET &&
 145                     AUDIT_MODE(profile) != AUDIT_ALL)
 146                         aad(&sa)->fs.request &= ~perms->quiet;
 147
 148                 if (!aad(&sa)->fs.request)
 149                         return COMPLAIN_MODE(profile) ? 0 : aad(&sa)->error;
 150         }
 151
 152         aad(&sa)->fs.denied = aad(&sa)->fs.request & ~perms->allow;
 153         return aa_audit(type, profile, &sa, file_audit_cb);
 154 }
 155
 156 /**
 157  * map_old_perms - map old file perms layout to the new layout
 158  * @old: permission set in old mapping
 159  *
 160  * Returns: new permission mapping
 161  */
 162 static u32 map_old_perms(u32 old)
 163 {
 164         u32 new = old & 0xf;
 165         if (old & MAY_READ)
 166                 new |= AA_MAY_META_READ;
 167         if (old & MAY_WRITE)
 168                 new |= AA_MAY_META_WRITE | AA_MAY_CREATE | AA_MAY_DELETE |
 169                         AA_MAY_CHMOD | AA_MAY_CHOWN;
 170         if (old & 0x10)
 171                 new |= AA_MAY_LINK;
 172         /* the old mapping lock and link_subset flags where overlaid
 173          * and use was determined by part of a pair that they were in
 174          */
 175         if (old & 0x20)
 176                 new |= AA_MAY_LOCK | AA_LINK_SUBSET;
 177         if (old & 0x40) /* AA_EXEC_MMAP */
 178                 new |= AA_EXEC_MMAP;
 179
 180         return new;
 181 }
 182
 183 /**
 184  * compute_perms - convert dfa compressed perms to internal perms
 185  * @dfa: dfa to compute perms for   (NOT NULL)
 186  * @state: state in dfa
 187  * @cond:  conditions to consider  (NOT NULL)
 188  *
 189  * TODO: convert from dfa + state to permission entry, do computation conversion
 190  *       at load time.
 191  *
 192  * Returns: computed permission set
 193  */
 194 static struct file_perms compute_perms(struct aa_dfa *dfa, unsigned int state,
 195                                        struct path_cond *cond)
 196 {
 197         struct file_perms perms;
 198
 199         /* FIXME: change over to new dfa format
 200          * currently file perms are encoded in the dfa, new format
 201          * splits the permissions from the dfa.  This mapping can be
 202          * done at profile load
 203          */
 204         perms.kill = 0;
 205
 206         if (uid_eq(current_fsuid(), cond->uid)) {
 207                 perms.allow = map_old_perms(dfa_user_allow(dfa, state));
 208                 perms.audit = map_old_perms(dfa_user_audit(dfa, state));
 209                 perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
 210                 perms.xindex = dfa_user_xindex(dfa, state);
 211         } else {
 212                 perms.allow = map_old_perms(dfa_other_allow(dfa, state));
 213                 perms.audit = map_old_perms(dfa_other_audit(dfa, state));
 214                 perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
 215                 perms.xindex = dfa_other_xindex(dfa, state);
 216         }
 217         perms.allow |= AA_MAY_META_READ;
 218
 219         /* change_profile wasn't determined by ownership in old mapping */
 220         if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
 221                 perms.allow |= AA_MAY_CHANGE_PROFILE;
 222         if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
 223                 perms.allow |= AA_MAY_ONEXEC;
 224
 225         return perms;
 226 }
 227
 228 /**
 229  * aa_str_perms - find permission that match @name
 230  * @dfa: to match against  (MAYBE NULL)
 231  * @state: state to start matching in
 232  * @name: string to match against dfa  (NOT NULL)
 233  * @cond: conditions to consider for permission set computation  (NOT NULL)
 234  * @perms: Returns - the permissions found when matching @name
 235  *
 236  * Returns: the final state in @dfa when beginning @start and walking @name
 237  */
 238 unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
 239                           const char *name, struct path_cond *cond,
 240                           struct file_perms *perms)
 241 {
 242         unsigned int state;
 243         if (!dfa) {
 244                 *perms = nullperms;
 245                 return DFA_NOMATCH;
 246         }
 247
 248         state = aa_dfa_match(dfa, start, name);
 249         *perms = compute_perms(dfa, state, cond);
 250
 251         return state;
 252 }
 253
 254 /**
 255  * is_deleted - test if a file has been completely unlinked
 256  * @dentry: dentry of file to test for deletion  (NOT NULL)
 257  *
 258  * Returns: %1 if deleted else %0
 259  */
 260 static inline bool is_deleted(struct dentry *dentry)
 261 {
 262         if (d_unlinked(dentry) && d_backing_inode(dentry)->i_nlink == 0)
 263                 return 1;
 264         return 0;
 265 }
 266
 267 /**
 268  * aa_path_perm - do permissions check & audit for @path
 269  * @op: operation being checked
 270  * @profile: profile being enforced  (NOT NULL)
 271  * @path: path to check permissions of  (NOT NULL)
 272  * @flags: any additional path flags beyond what the profile specifies
 273  * @request: requested permissions
 274  * @cond: conditional info for this request  (NOT NULL)
 275  *
 276  * Returns: %0 else error if access denied or other error
 277  */
 278 int aa_path_perm(const char *op, struct aa_profile *profile,
 279                  const struct path *path, int flags, u32 request,
 280                  struct path_cond *cond)
 281 {
 282         char *buffer = NULL;
 283         struct file_perms perms = {};
 284         const char *name, *info = NULL;
 285         int error;
 286
 287         flags |= profile->path_flags | (S_ISDIR(cond->mode) ? PATH_IS_DIR : 0);
 288         error = aa_path_name(path, flags, &buffer, &name, &info);
 289         if (error) {
 290                 if (error == -ENOENT && is_deleted(path->dentry)) {
 291                         /* Access to open files that are deleted are
 292                          * give a pass (implicit delegation)
 293                          */
 294                         error = 0;
 295                         info = NULL;
 296                         perms.allow = request;
 297                 }
 298         } else {
 299                 aa_str_perms(profile->file.dfa, profile->file.start, name, cond,
 300                              &perms);
 301                 if (request & ~perms.allow)
 302                         error = -EACCES;
 303         }
 304         error = aa_audit_file(profile, &perms, op, request, name, NULL,
 305                               cond->uid, info, error);
 306         kfree(buffer);
 307
 308         return error;
 309 }
 310
 311 /**
 312  * xindex_is_subset - helper for aa_path_link
 313  * @link: link permission set
 314  * @target: target permission set
 315  *
 316  * test target x permissions are equal OR a subset of link x permissions
 317  * this is done as part of the subset test, where a hardlink must have
 318  * a subset of permissions that the target has.
 319  *
 320  * Returns: %1 if subset else %0
 321  */
 322 static inline bool xindex_is_subset(u32 link, u32 target)
 323 {
 324         if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
 325             ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
 326                 return 0;
 327
 328         return 1;
 329 }
 330
 331 /**
 332  * aa_path_link - Handle hard link permission check
 333  * @profile: the profile being enforced  (NOT NULL)
 334  * @old_dentry: the target dentry  (NOT NULL)
 335  * @new_dir: directory the new link will be created in  (NOT NULL)
 336  * @new_dentry: the link being created  (NOT NULL)
 337  *
 338  * Handle the permission test for a link & target pair.  Permission
 339  * is encoded as a pair where the link permission is determined
 340  * first, and if allowed, the target is tested.  The target test
 341  * is done from the point of the link match (not start of DFA)
 342  * making the target permission dependent on the link permission match.
 343  *
 344  * The subset test if required forces that permissions granted
 345  * on link are a subset of the permission granted to target.
 346  *
 347  * Returns: %0 if allowed else error
 348  */
 349 int aa_path_link(struct aa_profile *profile, struct dentry *old_dentry,
 350                  const struct path *new_dir, struct dentry *new_dentry)
 351 {
 352         struct path link = { .mnt = new_dir->mnt, .dentry = new_dentry };
 353         struct path target = { .mnt = new_dir->mnt, .dentry = old_dentry };
 354         struct path_cond cond = {
 355                 d_backing_inode(old_dentry)->i_uid,
 356                 d_backing_inode(old_dentry)->i_mode
 357         };
 358         char *buffer = NULL, *buffer2 = NULL;
 359         const char *lname, *tname = NULL, *info = NULL;
 360         struct file_perms lperms, perms;
 361         u32 request = AA_MAY_LINK;
 362         unsigned int state;
 363         int error;
 364
 365         lperms = nullperms;
 366
 367         /* buffer freed below, lname is pointer in buffer */
 368         error = aa_path_name(&link, profile->path_flags, &buffer, &lname,
 369                              &info);
 370         if (error)
 371                 goto audit;
 372
 373         /* buffer2 freed below, tname is pointer in buffer2 */
 374         error = aa_path_name(&target, profile->path_flags, &buffer2, &tname,
 375                              &info);
 376         if (error)
 377                 goto audit;
 378
 379         error = -EACCES;
 380         /* aa_str_perms - handles the case of the dfa being NULL */
 381         state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
 382                              &cond, &lperms);
 383
 384         if (!(lperms.allow & AA_MAY_LINK))
 385                 goto audit;
 386
 387         /* test to see if target can be paired with link */
 388         state = aa_dfa_null_transition(profile->file.dfa, state);
 389         aa_str_perms(profile->file.dfa, state, tname, &cond, &perms);
 390
 391         /* force audit/quiet masks for link are stored in the second entry
 392          * in the link pair.
 393          */
 394         lperms.audit = perms.audit;
 395         lperms.quiet = perms.quiet;
 396         lperms.kill = perms.kill;
 397
 398         if (!(perms.allow & AA_MAY_LINK)) {
 399                 info = "target restricted";
 400                 goto audit;
 401         }
 402
 403         /* done if link subset test is not required */
 404         if (!(perms.allow & AA_LINK_SUBSET))
 405                 goto done_tests;
 406
 407         /* Do link perm subset test requiring allowed permission on link are a
 408          * subset of the allowed permissions on target.
 409          */
 410         aa_str_perms(profile->file.dfa, profile->file.start, tname, &cond,
 411                      &perms);
 412
 413         /* AA_MAY_LINK is not considered in the subset test */
 414         request = lperms.allow & ~AA_MAY_LINK;
 415         lperms.allow &= perms.allow | AA_MAY_LINK;
 416
 417         request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
 418         if (request & ~lperms.allow) {
 419                 goto audit;
 420         } else if ((lperms.allow & MAY_EXEC) &&
 421                    !xindex_is_subset(lperms.xindex, perms.xindex)) {
 422                 lperms.allow &= ~MAY_EXEC;
 423                 request |= MAY_EXEC;
 424                 info = "link not subset of target";
 425                 goto audit;
 426         }
 427
 428 done_tests:
 429         error = 0;
 430
 431 audit:
 432         error = aa_audit_file(profile, &lperms, OP_LINK, request,
 433                               lname, tname, cond.uid, info, error);
 434         kfree(buffer);
 435         kfree(buffer2);
 436
 437         return error;
 438 }
 439
 440 /**
 441  * aa_file_perm - do permission revalidation check & audit for @file
 442  * @op: operation being checked
 443  * @profile: profile being enforced   (NOT NULL)
 444  * @file: file to revalidate access permissions on  (NOT NULL)
 445  * @request: requested permissions
 446  *
 447  * Returns: %0 if access allowed else error
 448  */
 449 int aa_file_perm(const char *op, struct aa_profile *profile, struct file *file,
 450                  u32 request)
 451 {
 452         struct path_cond cond = {
 453                 .uid = file_inode(file)->i_uid,
 454                 .mode = file_inode(file)->i_mode
 455         };
 456
 457         return aa_path_perm(op, profile, &file->f_path, PATH_DELEGATE_DELETED,
 458                             request, &cond);
 459 }