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         uid_t fsuid = current_fsuid();
  69
  70         if (sa->aad.fs.request & AA_AUDIT_FILE_MASK) {
  71                 audit_log_format(ab, " requested_mask=");
  72                 audit_file_mask(ab, sa->aad.fs.request);
  73         }
  74         if (sa->aad.fs.denied & AA_AUDIT_FILE_MASK) {
  75                 audit_log_format(ab, " denied_mask=");
  76                 audit_file_mask(ab, sa->aad.fs.denied);
  77         }
  78         if (sa->aad.fs.request & AA_AUDIT_FILE_MASK) {
  79                 audit_log_format(ab, " fsuid=%d", fsuid);
  80                 audit_log_format(ab, " ouid=%d", sa->aad.fs.ouid);
  81         }
  82
  83         if (sa->aad.fs.target) {
  84                 audit_log_format(ab, " target=");
  85                 audit_log_untrustedstring(ab, sa->aad.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  * @gfp: allocation flags
  94  * @op: operation being mediated
  95  * @request: permissions requested
  96  * @name: name of object being mediated (MAYBE NULL)
  97  * @target: name of target (MAYBE 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  */
 104 int aa_audit_file(struct aa_profile *profile, struct file_perms *perms,
 105                   gfp_t gfp, int op, u32 request, const char *name,
 106                   const char *target, uid_t ouid, const char *info, int error)
 107 {
 108         int type = AUDIT_APPARMOR_AUTO;
 109         struct common_audit_data sa;
 110         COMMON_AUDIT_DATA_INIT(&sa, NONE);
 111         sa.aad.op = op,
 112         sa.aad.fs.request = request;
 113         sa.aad.name = name;
 114         sa.aad.fs.target = target;
 115         sa.aad.fs.ouid = ouid;
 116         sa.aad.info = info;
 117         sa.aad.error = error;
 118
 119         if (likely(!sa.aad.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                 sa.aad.fs.request &= mask;
 127
 128                 if (likely(!sa.aad.fs.request))
 129                         return 0;
 130                 type = AUDIT_APPARMOR_AUDIT;
 131         } else {
 132                 /* only report permissions that were denied */
 133                 sa.aad.fs.request = sa.aad.fs.request & ~perms->allow;
 134
 135                 if (sa.aad.fs.request & perms->kill)
 136                         type = AUDIT_APPARMOR_KILL;
 137
 138                 /* quiet known rejects, assumes quiet and kill do not overlap */
 139                 if ((sa.aad.fs.request & perms->quiet) &&
 140                     AUDIT_MODE(profile) != AUDIT_NOQUIET &&
 141                     AUDIT_MODE(profile) != AUDIT_ALL)
 142                         sa.aad.fs.request &= ~perms->quiet;
 143
 144                 if (!sa.aad.fs.request)
 145                         return COMPLAIN_MODE(profile) ? 0 : sa.aad.error;
 146         }
 147
 148         sa.aad.fs.denied = sa.aad.fs.request & ~perms->allow;
 149         return aa_audit(type, profile, gfp, &sa, file_audit_cb);
 150 }
 151
 152 /**
 153  * map_old_perms - map old file perms layout to the new layout
 154  * @old: permission set in old mapping
 155  *
 156  * Returns: new permission mapping
 157  */
 158 static u32 map_old_perms(u32 old)
 159 {
 160         u32 new = old & 0xf;
 161         if (old & MAY_READ)
 162                 new |= AA_MAY_META_READ;
 163         if (old & MAY_WRITE)
 164                 new |= AA_MAY_META_WRITE | AA_MAY_CREATE | AA_MAY_DELETE |
 165                         AA_MAY_CHMOD | AA_MAY_CHOWN;
 166         if (old & 0x10)
 167                 new |= AA_MAY_LINK;
 168         /* the old mapping lock and link_subset flags where overlaid
 169          * and use was determined by part of a pair that they were in
 170          */
 171         if (old & 0x20)
 172                 new |= AA_MAY_LOCK | AA_LINK_SUBSET;
 173         if (old & 0x40) /* AA_EXEC_MMAP */
 174                 new |= AA_EXEC_MMAP;
 175
 176         return new;
 177 }
 178
 179 /**
 180  * compute_perms - convert dfa compressed perms to internal perms
 181  * @dfa: dfa to compute perms for   (NOT NULL)
 182  * @state: state in dfa
 183  * @cond:  conditions to consider  (NOT NULL)
 184  *
 185  * TODO: convert from dfa + state to permission entry, do computation conversion
 186  *       at load time.
 187  *
 188  * Returns: computed permission set
 189  */
 190 static struct file_perms compute_perms(struct aa_dfa *dfa, unsigned int state,
 191                                        struct path_cond *cond)
 192 {
 193         struct file_perms perms;
 194
 195         /* FIXME: change over to new dfa format
 196          * currently file perms are encoded in the dfa, new format
 197          * splits the permissions from the dfa.  This mapping can be
 198          * done at profile load
 199          */
 200         perms.kill = 0;
 201
 202         if (current_fsuid() == cond->uid) {
 203                 perms.allow = map_old_perms(dfa_user_allow(dfa, state));
 204                 perms.audit = map_old_perms(dfa_user_audit(dfa, state));
 205                 perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
 206                 perms.xindex = dfa_user_xindex(dfa, state);
 207         } else {
 208                 perms.allow = map_old_perms(dfa_other_allow(dfa, state));
 209                 perms.audit = map_old_perms(dfa_other_audit(dfa, state));
 210                 perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
 211                 perms.xindex = dfa_other_xindex(dfa, state);
 212         }
 213         perms.allow |= AA_MAY_META_READ;
 214
 215         /* change_profile wasn't determined by ownership in old mapping */
 216         if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
 217                 perms.allow |= AA_MAY_CHANGE_PROFILE;
 218
 219         return perms;
 220 }
 221
 222 /**
 223  * aa_str_perms - find permission that match @name
 224  * @dfa: to match against  (MAYBE NULL)
 225  * @state: state to start matching in
 226  * @name: string to match against dfa  (NOT NULL)
 227  * @cond: conditions to consider for permission set computation  (NOT NULL)
 228  * @perms: Returns - the permissions found when matching @name
 229  *
 230  * Returns: the final state in @dfa when beginning @start and walking @name
 231  */
 232 unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
 233                           const char *name, struct path_cond *cond,
 234                           struct file_perms *perms)
 235 {
 236         unsigned int state;
 237         if (!dfa) {
 238                 *perms = nullperms;
 239                 return DFA_NOMATCH;
 240         }
 241
 242         state = aa_dfa_match(dfa, start, name);
 243         *perms = compute_perms(dfa, state, cond);
 244
 245         return state;
 246 }
 247
 248 /**
 249  * is_deleted - test if a file has been completely unlinked
 250  * @dentry: dentry of file to test for deletion  (NOT NULL)
 251  *
 252  * Returns: %1 if deleted else %0
 253  */
 254 static inline bool is_deleted(struct dentry *dentry)
 255 {
 256         if (d_unlinked(dentry) && dentry->d_inode->i_nlink == 0)
 257                 return 1;
 258         return 0;
 259 }
 260
 261 /**
 262  * aa_path_perm - do permissions check & audit for @path
 263  * @op: operation being checked
 264  * @profile: profile being enforced  (NOT NULL)
 265  * @path: path to check permissions of  (NOT NULL)
 266  * @flags: any additional path flags beyond what the profile specifies
 267  * @request: requested permissions
 268  * @cond: conditional info for this request  (NOT NULL)
 269  *
 270  * Returns: %0 else error if access denied or other error
 271  */
 272 int aa_path_perm(int op, struct aa_profile *profile, struct path *path,
 273                  int flags, u32 request, struct path_cond *cond)
 274 {
 275         char *buffer = NULL;
 276         struct file_perms perms = {};
 277         const char *name, *info = NULL;
 278         int error;
 279
 280         flags |= profile->path_flags | (S_ISDIR(cond->mode) ? PATH_IS_DIR : 0);
 281         error = aa_path_name(path, flags, &buffer, &name, &info);
 282         if (error) {
 283                 if (error == -ENOENT && is_deleted(path->dentry)) {
 284                         /* Access to open files that are deleted are
 285                          * give a pass (implicit delegation)
 286                          */
 287                         error = 0;
 288                         info = NULL;
 289                         perms.allow = request;
 290                 }
 291         } else {
 292                 aa_str_perms(profile->file.dfa, profile->file.start, name, cond,
 293                              &perms);
 294                 if (request & ~perms.allow)
 295                         error = -EACCES;
 296         }
 297         error = aa_audit_file(profile, &perms, GFP_KERNEL, op, request, name,
 298                               NULL, cond->uid, info, error);
 299         kfree(buffer);
 300
 301         return error;
 302 }
 303
 304 /**
 305  * xindex_is_subset - helper for aa_path_link
 306  * @link: link permission set
 307  * @target: target permission set
 308  *
 309  * test target x permissions are equal OR a subset of link x permissions
 310  * this is done as part of the subset test, where a hardlink must have
 311  * a subset of permissions that the target has.
 312  *
 313  * Returns: %1 if subset else %0
 314  */
 315 static inline bool xindex_is_subset(u32 link, u32 target)
 316 {
 317         if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
 318             ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
 319                 return 0;
 320
 321         return 1;
 322 }
 323
 324 /**
 325  * aa_path_link - Handle hard link permission check
 326  * @profile: the profile being enforced  (NOT NULL)
 327  * @old_dentry: the target dentry  (NOT NULL)
 328  * @new_dir: directory the new link will be created in  (NOT NULL)
 329  * @new_dentry: the link being created  (NOT NULL)
 330  *
 331  * Handle the permission test for a link & target pair.  Permission
 332  * is encoded as a pair where the link permission is determined
 333  * first, and if allowed, the target is tested.  The target test
 334  * is done from the point of the link match (not start of DFA)
 335  * making the target permission dependent on the link permission match.
 336  *
 337  * The subset test if required forces that permissions granted
 338  * on link are a subset of the permission granted to target.
 339  *
 340  * Returns: %0 if allowed else error
 341  */
 342 int aa_path_link(struct aa_profile *profile, struct dentry *old_dentry,
 343                  struct path *new_dir, struct dentry *new_dentry)
 344 {
 345         struct path link = { new_dir->mnt, new_dentry };
 346         struct path target = { new_dir->mnt, old_dentry };
 347         struct path_cond cond = {
 348                 old_dentry->d_inode->i_uid,
 349                 old_dentry->d_inode->i_mode
 350         };
 351         char *buffer = NULL, *buffer2 = NULL;
 352         const char *lname, *tname = NULL, *info = NULL;
 353         struct file_perms lperms, perms;
 354         u32 request = AA_MAY_LINK;
 355         unsigned int state;
 356         int error;
 357
 358         lperms = nullperms;
 359
 360         /* buffer freed below, lname is pointer in buffer */
 361         error = aa_path_name(&link, profile->path_flags, &buffer, &lname,
 362                              &info);
 363         if (error)
 364                 goto audit;
 365
 366         /* buffer2 freed below, tname is pointer in buffer2 */
 367         error = aa_path_name(&target, profile->path_flags, &buffer2, &tname,
 368                              &info);
 369         if (error)
 370                 goto audit;
 371
 372         error = -EACCES;
 373         /* aa_str_perms - handles the case of the dfa being NULL */
 374         state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
 375                              &cond, &lperms);
 376
 377         if (!(lperms.allow & AA_MAY_LINK))
 378                 goto audit;
 379
 380         /* test to see if target can be paired with link */
 381         state = aa_dfa_null_transition(profile->file.dfa, state);
 382         aa_str_perms(profile->file.dfa, state, tname, &cond, &perms);
 383
 384         /* force audit/quiet masks for link are stored in the second entry
 385          * in the link pair.
 386          */
 387         lperms.audit = perms.audit;
 388         lperms.quiet = perms.quiet;
 389         lperms.kill = perms.kill;
 390
 391         if (!(perms.allow & AA_MAY_LINK)) {
 392                 info = "target restricted";
 393                 goto audit;
 394         }
 395
 396         /* done if link subset test is not required */
 397         if (!(perms.allow & AA_LINK_SUBSET))
 398                 goto done_tests;
 399
 400         /* Do link perm subset test requiring allowed permission on link are a
 401          * subset of the allowed permissions on target.
 402          */
 403         aa_str_perms(profile->file.dfa, profile->file.start, tname, &cond,
 404                      &perms);
 405
 406         /* AA_MAY_LINK is not considered in the subset test */
 407         request = lperms.allow & ~AA_MAY_LINK;
 408         lperms.allow &= perms.allow | AA_MAY_LINK;
 409
 410         request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
 411         if (request & ~lperms.allow) {
 412                 goto audit;
 413         } else if ((lperms.allow & MAY_EXEC) &&
 414                    !xindex_is_subset(lperms.xindex, perms.xindex)) {
 415                 lperms.allow &= ~MAY_EXEC;
 416                 request |= MAY_EXEC;
 417                 info = "link not subset of target";
 418                 goto audit;
 419         }
 420
 421 done_tests:
 422         error = 0;
 423
 424 audit:
 425         error = aa_audit_file(profile, &lperms, GFP_KERNEL, OP_LINK, request,
 426                               lname, tname, cond.uid, info, error);
 427         kfree(buffer);
 428         kfree(buffer2);
 429
 430         return error;
 431 }
 432
 433 /**
 434  * aa_file_perm - do permission revalidation check & audit for @file
 435  * @op: operation being checked
 436  * @profile: profile being enforced   (NOT NULL)
 437  * @file: file to revalidate access permissions on  (NOT NULL)
 438  * @request: requested permissions
 439  *
 440  * Returns: %0 if access allowed else error
 441  */
 442 int aa_file_perm(int op, struct aa_profile *profile, struct file *file,
 443                  u32 request)
 444 {
 445         struct path_cond cond = {
 446                 .uid = file->f_path.dentry->d_inode->i_uid,
 447                 .mode = file->f_path.dentry->d_inode->i_mode
 448         };
 449
 450         return aa_path_perm(op, profile, &file->f_path, PATH_DELEGATE_DELETED,
 451                             request, &cond);
 452 }