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         struct apparmor_audit_data aad = {0,};
 111         COMMON_AUDIT_DATA_INIT(&sa, NONE);
 112         sa.aad = &aad;
 113         aad.op = op,
 114         aad.fs.request = request;
 115         aad.name = name;
 116         aad.fs.target = target;
 117         aad.fs.ouid = ouid;
 118         aad.info = info;
 119         aad.error = error;
 120
 121         if (likely(!sa.aad->error)) {
 122                 u32 mask = perms->audit;
 123
 124                 if (unlikely(AUDIT_MODE(profile) == AUDIT_ALL))
 125                         mask = 0xffff;
 126
 127                 /* mask off perms that are not being force audited */
 128                 sa.aad->fs.request &= mask;
 129
 130                 if (likely(!sa.aad->fs.request))
 131                         return 0;
 132                 type = AUDIT_APPARMOR_AUDIT;
 133         } else {
 134                 /* only report permissions that were denied */
 135                 sa.aad->fs.request = sa.aad->fs.request & ~perms->allow;
 136
 137                 if (sa.aad->fs.request & perms->kill)
 138                         type = AUDIT_APPARMOR_KILL;
 139
 140                 /* quiet known rejects, assumes quiet and kill do not overlap */
 141                 if ((sa.aad->fs.request & perms->quiet) &&
 142                     AUDIT_MODE(profile) != AUDIT_NOQUIET &&
 143                     AUDIT_MODE(profile) != AUDIT_ALL)
 144                         sa.aad->fs.request &= ~perms->quiet;
 145
 146                 if (!sa.aad->fs.request)
 147                         return COMPLAIN_MODE(profile) ? 0 : sa.aad->error;
 148         }
 149
 150         sa.aad->fs.denied = sa.aad->fs.request & ~perms->allow;
 151         return aa_audit(type, profile, gfp, &sa, file_audit_cb);
 152 }
 153
 154 /**
 155  * map_old_perms - map old file perms layout to the new layout
 156  * @old: permission set in old mapping
 157  *
 158  * Returns: new permission mapping
 159  */
 160 static u32 map_old_perms(u32 old)
 161 {
 162         u32 new = old & 0xf;
 163         if (old & MAY_READ)
 164                 new |= AA_MAY_META_READ;
 165         if (old & MAY_WRITE)
 166                 new |= AA_MAY_META_WRITE | AA_MAY_CREATE | AA_MAY_DELETE |
 167                         AA_MAY_CHMOD | AA_MAY_CHOWN;
 168         if (old & 0x10)
 169                 new |= AA_MAY_LINK;
 170         /* the old mapping lock and link_subset flags where overlaid
 171          * and use was determined by part of a pair that they were in
 172          */
 173         if (old & 0x20)
 174                 new |= AA_MAY_LOCK | AA_LINK_SUBSET;
 175         if (old & 0x40) /* AA_EXEC_MMAP */
 176                 new |= AA_EXEC_MMAP;
 177
 178         return new;
 179 }
 180
 181 /**
 182  * compute_perms - convert dfa compressed perms to internal perms
 183  * @dfa: dfa to compute perms for   (NOT NULL)
 184  * @state: state in dfa
 185  * @cond:  conditions to consider  (NOT NULL)
 186  *
 187  * TODO: convert from dfa + state to permission entry, do computation conversion
 188  *       at load time.
 189  *
 190  * Returns: computed permission set
 191  */
 192 static struct file_perms compute_perms(struct aa_dfa *dfa, unsigned int state,
 193                                        struct path_cond *cond)
 194 {
 195         struct file_perms perms;
 196
 197         /* FIXME: change over to new dfa format
 198          * currently file perms are encoded in the dfa, new format
 199          * splits the permissions from the dfa.  This mapping can be
 200          * done at profile load
 201          */
 202         perms.kill = 0;
 203
 204         if (current_fsuid() == cond->uid) {
 205                 perms.allow = map_old_perms(dfa_user_allow(dfa, state));
 206                 perms.audit = map_old_perms(dfa_user_audit(dfa, state));
 207                 perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
 208                 perms.xindex = dfa_user_xindex(dfa, state);
 209         } else {
 210                 perms.allow = map_old_perms(dfa_other_allow(dfa, state));
 211                 perms.audit = map_old_perms(dfa_other_audit(dfa, state));
 212                 perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
 213                 perms.xindex = dfa_other_xindex(dfa, state);
 214         }
 215         perms.allow |= AA_MAY_META_READ;
 216
 217         /* change_profile wasn't determined by ownership in old mapping */
 218         if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
 219                 perms.allow |= AA_MAY_CHANGE_PROFILE;
 220         if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
 221                 perms.allow |= AA_MAY_ONEXEC;
 222
 223         return perms;
 224 }
 225
 226 /**
 227  * aa_str_perms - find permission that match @name
 228  * @dfa: to match against  (MAYBE NULL)
 229  * @state: state to start matching in
 230  * @name: string to match against dfa  (NOT NULL)
 231  * @cond: conditions to consider for permission set computation  (NOT NULL)
 232  * @perms: Returns - the permissions found when matching @name
 233  *
 234  * Returns: the final state in @dfa when beginning @start and walking @name
 235  */
 236 unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
 237                           const char *name, struct path_cond *cond,
 238                           struct file_perms *perms)
 239 {
 240         unsigned int state;
 241         if (!dfa) {
 242                 *perms = nullperms;
 243                 return DFA_NOMATCH;
 244         }
 245
 246         state = aa_dfa_match(dfa, start, name);
 247         *perms = compute_perms(dfa, state, cond);
 248
 249         return state;
 250 }
 251
 252 /**
 253  * is_deleted - test if a file has been completely unlinked
 254  * @dentry: dentry of file to test for deletion  (NOT NULL)
 255  *
 256  * Returns: %1 if deleted else %0
 257  */
 258 static inline bool is_deleted(struct dentry *dentry)
 259 {
 260         if (d_unlinked(dentry) && dentry->d_inode->i_nlink == 0)
 261                 return 1;
 262         return 0;
 263 }
 264
 265 /**
 266  * aa_path_perm - do permissions check & audit for @path
 267  * @op: operation being checked
 268  * @profile: profile being enforced  (NOT NULL)
 269  * @path: path to check permissions of  (NOT NULL)
 270  * @flags: any additional path flags beyond what the profile specifies
 271  * @request: requested permissions
 272  * @cond: conditional info for this request  (NOT NULL)
 273  *
 274  * Returns: %0 else error if access denied or other error
 275  */
 276 int aa_path_perm(int op, struct aa_profile *profile, struct path *path,
 277                  int flags, u32 request, struct path_cond *cond)
 278 {
 279         char *buffer = NULL;
 280         struct file_perms perms = {};
 281         const char *name, *info = NULL;
 282         int error;
 283
 284         flags |= profile->path_flags | (S_ISDIR(cond->mode) ? PATH_IS_DIR : 0);
 285         error = aa_path_name(path, flags, &buffer, &name, &info);
 286         if (error) {
 287                 if (error == -ENOENT && is_deleted(path->dentry)) {
 288                         /* Access to open files that are deleted are
 289                          * give a pass (implicit delegation)
 290                          */
 291                         error = 0;
 292                         info = NULL;
 293                         perms.allow = request;
 294                 }
 295         } else {
 296                 aa_str_perms(profile->file.dfa, profile->file.start, name, cond,
 297                              &perms);
 298                 if (request & ~perms.allow)
 299                         error = -EACCES;
 300         }
 301         error = aa_audit_file(profile, &perms, GFP_KERNEL, op, request, name,
 302                               NULL, cond->uid, info, error);
 303         kfree(buffer);
 304
 305         return error;
 306 }
 307
 308 /**
 309  * xindex_is_subset - helper for aa_path_link
 310  * @link: link permission set
 311  * @target: target permission set
 312  *
 313  * test target x permissions are equal OR a subset of link x permissions
 314  * this is done as part of the subset test, where a hardlink must have
 315  * a subset of permissions that the target has.
 316  *
 317  * Returns: %1 if subset else %0
 318  */
 319 static inline bool xindex_is_subset(u32 link, u32 target)
 320 {
 321         if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
 322             ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
 323                 return 0;
 324
 325         return 1;
 326 }
 327
 328 /**
 329  * aa_path_link - Handle hard link permission check
 330  * @profile: the profile being enforced  (NOT NULL)
 331  * @old_dentry: the target dentry  (NOT NULL)
 332  * @new_dir: directory the new link will be created in  (NOT NULL)
 333  * @new_dentry: the link being created  (NOT NULL)
 334  *
 335  * Handle the permission test for a link & target pair.  Permission
 336  * is encoded as a pair where the link permission is determined
 337  * first, and if allowed, the target is tested.  The target test
 338  * is done from the point of the link match (not start of DFA)
 339  * making the target permission dependent on the link permission match.
 340  *
 341  * The subset test if required forces that permissions granted
 342  * on link are a subset of the permission granted to target.
 343  *
 344  * Returns: %0 if allowed else error
 345  */
 346 int aa_path_link(struct aa_profile *profile, struct dentry *old_dentry,
 347                  struct path *new_dir, struct dentry *new_dentry)
 348 {
 349         struct path link = { new_dir->mnt, new_dentry };
 350         struct path target = { new_dir->mnt, old_dentry };
 351         struct path_cond cond = {
 352                 old_dentry->d_inode->i_uid,
 353                 old_dentry->d_inode->i_mode
 354         };
 355         char *buffer = NULL, *buffer2 = NULL;
 356         const char *lname, *tname = NULL, *info = NULL;
 357         struct file_perms lperms, perms;
 358         u32 request = AA_MAY_LINK;
 359         unsigned int state;
 360         int error;
 361
 362         lperms = nullperms;
 363
 364         /* buffer freed below, lname is pointer in buffer */
 365         error = aa_path_name(&link, profile->path_flags, &buffer, &lname,
 366                              &info);
 367         if (error)
 368                 goto audit;
 369
 370         /* buffer2 freed below, tname is pointer in buffer2 */
 371         error = aa_path_name(&target, profile->path_flags, &buffer2, &tname,
 372                              &info);
 373         if (error)
 374                 goto audit;
 375
 376         error = -EACCES;
 377         /* aa_str_perms - handles the case of the dfa being NULL */
 378         state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
 379                              &cond, &lperms);
 380
 381         if (!(lperms.allow & AA_MAY_LINK))
 382                 goto audit;
 383
 384         /* test to see if target can be paired with link */
 385         state = aa_dfa_null_transition(profile->file.dfa, state);
 386         aa_str_perms(profile->file.dfa, state, tname, &cond, &perms);
 387
 388         /* force audit/quiet masks for link are stored in the second entry
 389          * in the link pair.
 390          */
 391         lperms.audit = perms.audit;
 392         lperms.quiet = perms.quiet;
 393         lperms.kill = perms.kill;
 394
 395         if (!(perms.allow & AA_MAY_LINK)) {
 396                 info = "target restricted";
 397                 goto audit;
 398         }
 399
 400         /* done if link subset test is not required */
 401         if (!(perms.allow & AA_LINK_SUBSET))
 402                 goto done_tests;
 403
 404         /* Do link perm subset test requiring allowed permission on link are a
 405          * subset of the allowed permissions on target.
 406          */
 407         aa_str_perms(profile->file.dfa, profile->file.start, tname, &cond,
 408                      &perms);
 409
 410         /* AA_MAY_LINK is not considered in the subset test */
 411         request = lperms.allow & ~AA_MAY_LINK;
 412         lperms.allow &= perms.allow | AA_MAY_LINK;
 413
 414         request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
 415         if (request & ~lperms.allow) {
 416                 goto audit;
 417         } else if ((lperms.allow & MAY_EXEC) &&
 418                    !xindex_is_subset(lperms.xindex, perms.xindex)) {
 419                 lperms.allow &= ~MAY_EXEC;
 420                 request |= MAY_EXEC;
 421                 info = "link not subset of target";
 422                 goto audit;
 423         }
 424
 425 done_tests:
 426         error = 0;
 427
 428 audit:
 429         error = aa_audit_file(profile, &lperms, GFP_KERNEL, OP_LINK, request,
 430                               lname, tname, cond.uid, info, error);
 431         kfree(buffer);
 432         kfree(buffer2);
 433
 434         return error;
 435 }
 436
 437 /**
 438  * aa_file_perm - do permission revalidation check & audit for @file
 439  * @op: operation being checked
 440  * @profile: profile being enforced   (NOT NULL)
 441  * @file: file to revalidate access permissions on  (NOT NULL)
 442  * @request: requested permissions
 443  *
 444  * Returns: %0 if access allowed else error
 445  */
 446 int aa_file_perm(int op, struct aa_profile *profile, struct file *file,
 447                  u32 request)
 448 {
 449         struct path_cond cond = {
 450                 .uid = file->f_path.dentry->d_inode->i_uid,
 451                 .mode = file->f_path.dentry->d_inode->i_mode
 452         };
 453
 454         return aa_path_perm(op, profile, &file->f_path, PATH_DELEGATE_DELETED,
 455                             request, &cond);
 456 }