fs/posix_acl.c

   1 /*
   2  * linux/fs/posix_acl.c
   3  *
   4  *  Copyright (C) 2002 by Andreas Gruenbacher <a.gruenbacher@computer.org>
   5  *
   6  *  Fixes from William Schumacher incorporated on 15 March 2001.
   7  *     (Reported by Charles Bertsch, <CBertsch@microtest.com>).
   8  */
   9
  10 /*
  11  *  This file contains generic functions for manipulating
  12  *  POSIX 1003.1e draft standard 17 ACLs.
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/slab.h>
  17 #include <linux/atomic.h>
  18 #include <linux/fs.h>
  19 #include <linux/sched.h>
  20 #include <linux/posix_acl.h>
  21 #include <linux/module.h>
  22
  23 #include <linux/errno.h>
  24
  25 EXPORT_SYMBOL(posix_acl_init);
  26 EXPORT_SYMBOL(posix_acl_alloc);
  27 EXPORT_SYMBOL(posix_acl_valid);
  28 EXPORT_SYMBOL(posix_acl_equiv_mode);
  29 EXPORT_SYMBOL(posix_acl_from_mode);
  30
  31 /*
  32  * Init a fresh posix_acl
  33  */
  34 void
  35 posix_acl_init(struct posix_acl *acl, int count)
  36 {
  37         atomic_set(&acl->a_refcount, 1);
  38         acl->a_count = count;
  39 }
  40
  41 /*
  42  * Allocate a new ACL with the specified number of entries.
  43  */
  44 struct posix_acl *
  45 posix_acl_alloc(int count, gfp_t flags)
  46 {
  47         const size_t size = sizeof(struct posix_acl) +
  48                             count * sizeof(struct posix_acl_entry);
  49         struct posix_acl *acl = kmalloc(size, flags);
  50         if (acl)
  51                 posix_acl_init(acl, count);
  52         return acl;
  53 }
  54
  55 /*
  56  * Clone an ACL.
  57  */
  58 static struct posix_acl *
  59 posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
  60 {
  61         struct posix_acl *clone = NULL;
  62
  63         if (acl) {
  64                 int size = sizeof(struct posix_acl) + acl->a_count *
  65                            sizeof(struct posix_acl_entry);
  66                 clone = kmemdup(acl, size, flags);
  67                 if (clone)
  68                         atomic_set(&clone->a_refcount, 1);
  69         }
  70         return clone;
  71 }
  72
  73 /*
  74  * Check if an acl is valid. Returns 0 if it is, or -E... otherwise.
  75  */
  76 int
  77 posix_acl_valid(const struct posix_acl *acl)
  78 {
  79         const struct posix_acl_entry *pa, *pe;
  80         int state = ACL_USER_OBJ;
  81         unsigned int id = 0;  /* keep gcc happy */
  82         int needs_mask = 0;
  83
  84         FOREACH_ACL_ENTRY(pa, acl, pe) {
  85                 if (pa->e_perm & ~(ACL_READ|ACL_WRITE|ACL_EXECUTE))
  86                         return -EINVAL;
  87                 switch (pa->e_tag) {
  88                         case ACL_USER_OBJ:
  89                                 if (state == ACL_USER_OBJ) {
  90                                         id = 0;
  91                                         state = ACL_USER;
  92                                         break;
  93                                 }
  94                                 return -EINVAL;
  95
  96                         case ACL_USER:
  97                                 if (state != ACL_USER)
  98                                         return -EINVAL;
  99                                 if (pa->e_id == ACL_UNDEFINED_ID ||
 100                                     pa->e_id < id)
 101                                         return -EINVAL;
 102                                 id = pa->e_id + 1;
 103                                 needs_mask = 1;
 104                                 break;
 105
 106                         case ACL_GROUP_OBJ:
 107                                 if (state == ACL_USER) {
 108                                         id = 0;
 109                                         state = ACL_GROUP;
 110                                         break;
 111                                 }
 112                                 return -EINVAL;
 113
 114                         case ACL_GROUP:
 115                                 if (state != ACL_GROUP)
 116                                         return -EINVAL;
 117                                 if (pa->e_id == ACL_UNDEFINED_ID ||
 118                                     pa->e_id < id)
 119                                         return -EINVAL;
 120                                 id = pa->e_id + 1;
 121                                 needs_mask = 1;
 122                                 break;
 123
 124                         case ACL_MASK:
 125                                 if (state != ACL_GROUP)
 126                                         return -EINVAL;
 127                                 state = ACL_OTHER;
 128                                 break;
 129
 130                         case ACL_OTHER:
 131                                 if (state == ACL_OTHER ||
 132                                     (state == ACL_GROUP && !needs_mask)) {
 133                                         state = 0;
 134                                         break;
 135                                 }
 136                                 return -EINVAL;
 137
 138                         default:
 139                                 return -EINVAL;
 140                 }
 141         }
 142         if (state == 0)
 143                 return 0;
 144         return -EINVAL;
 145 }
 146
 147 /*
 148  * Returns 0 if the acl can be exactly represented in the traditional
 149  * file mode permission bits, or else 1. Returns -E... on error.
 150  */
 151 int
 152 posix_acl_equiv_mode(const struct posix_acl *acl, umode_t *mode_p)
 153 {
 154         const struct posix_acl_entry *pa, *pe;
 155         umode_t mode = 0;
 156         int not_equiv = 0;
 157
 158         /*
 159          * A null ACL can always be presented as mode bits.
 160          */
 161         if (!acl)
 162                 return 0;
 163
 164         FOREACH_ACL_ENTRY(pa, acl, pe) {
 165                 switch (pa->e_tag) {
 166                         case ACL_USER_OBJ:
 167                                 mode |= (pa->e_perm & S_IRWXO) << 6;
 168                                 break;
 169                         case ACL_GROUP_OBJ:
 170                                 mode |= (pa->e_perm & S_IRWXO) << 3;
 171                                 break;
 172                         case ACL_OTHER:
 173                                 mode |= pa->e_perm & S_IRWXO;
 174                                 break;
 175                         case ACL_MASK:
 176                                 mode = (mode & ~S_IRWXG) |
 177                                        ((pa->e_perm & S_IRWXO) << 3);
 178                                 not_equiv = 1;
 179                                 break;
 180                         case ACL_USER:
 181                         case ACL_GROUP:
 182                                 not_equiv = 1;
 183                                 break;
 184                         default:
 185                                 return -EINVAL;
 186                 }
 187         }
 188         if (mode_p)
 189                 *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 190         return not_equiv;
 191 }
 192
 193 /*
 194  * Create an ACL representing the file mode permission bits of an inode.
 195  */
 196 struct posix_acl *
 197 posix_acl_from_mode(umode_t mode, gfp_t flags)
 198 {
 199         struct posix_acl *acl = posix_acl_alloc(3, flags);
 200         if (!acl)
 201                 return ERR_PTR(-ENOMEM);
 202
 203         acl->a_entries[0].e_tag  = ACL_USER_OBJ;
 204         acl->a_entries[0].e_id   = ACL_UNDEFINED_ID;
 205         acl->a_entries[0].e_perm = (mode & S_IRWXU) >> 6;
 206
 207         acl->a_entries[1].e_tag  = ACL_GROUP_OBJ;
 208         acl->a_entries[1].e_id   = ACL_UNDEFINED_ID;
 209         acl->a_entries[1].e_perm = (mode & S_IRWXG) >> 3;
 210
 211         acl->a_entries[2].e_tag  = ACL_OTHER;
 212         acl->a_entries[2].e_id   = ACL_UNDEFINED_ID;
 213         acl->a_entries[2].e_perm = (mode & S_IRWXO);
 214         return acl;
 215 }
 216
 217 /*
 218  * Return 0 if current is granted want access to the inode
 219  * by the acl. Returns -E... otherwise.
 220  */
 221 int
 222 posix_acl_permission(struct inode *inode, const struct posix_acl *acl, int want)
 223 {
 224         const struct posix_acl_entry *pa, *pe, *mask_obj;
 225         int found = 0;
 226
 227         want &= MAY_READ | MAY_WRITE | MAY_EXEC | MAY_NOT_BLOCK;
 228
 229         FOREACH_ACL_ENTRY(pa, acl, pe) {
 230                 switch(pa->e_tag) {
 231                         case ACL_USER_OBJ:
 232                                 /* (May have been checked already) */
 233                                 if (inode->i_uid == current_fsuid())
 234                                         goto check_perm;
 235                                 break;
 236                         case ACL_USER:
 237                                 if (pa->e_id == current_fsuid())
 238                                         goto mask;
 239                                 break;
 240                         case ACL_GROUP_OBJ:
 241                                 if (in_group_p(inode->i_gid)) {
 242                                         found = 1;
 243                                         if ((pa->e_perm & want) == want)
 244                                                 goto mask;
 245                                 }
 246                                 break;
 247                         case ACL_GROUP:
 248                                 if (in_group_p(pa->e_id)) {
 249                                         found = 1;
 250                                         if ((pa->e_perm & want) == want)
 251                                                 goto mask;
 252                                 }
 253                                 break;
 254                         case ACL_MASK:
 255                                 break;
 256                         case ACL_OTHER:
 257                                 if (found)
 258                                         return -EACCES;
 259                                 else
 260                                         goto check_perm;
 261                         default:
 262                                 return -EIO;
 263                 }
 264         }
 265         return -EIO;
 266
 267 mask:
 268         for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
 269                 if (mask_obj->e_tag == ACL_MASK) {
 270                         if ((pa->e_perm & mask_obj->e_perm & want) == want)
 271                                 return 0;
 272                         return -EACCES;
 273                 }
 274         }
 275
 276 check_perm:
 277         if ((pa->e_perm & want) == want)
 278                 return 0;
 279         return -EACCES;
 280 }
 281
 282 /*
 283  * Modify acl when creating a new inode. The caller must ensure the acl is
 284  * only referenced once.
 285  *
 286  * mode_p initially must contain the mode parameter to the open() / creat()
 287  * system calls. All permissions that are not granted by the acl are removed.
 288  * The permissions in the acl are changed to reflect the mode_p parameter.
 289  */
 290 static int posix_acl_create_masq(struct posix_acl *acl, umode_t *mode_p)
 291 {
 292         struct posix_acl_entry *pa, *pe;
 293         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 294         umode_t mode = *mode_p;
 295         int not_equiv = 0;
 296
 297         /* assert(atomic_read(acl->a_refcount) == 1); */
 298
 299         FOREACH_ACL_ENTRY(pa, acl, pe) {
 300                 switch(pa->e_tag) {
 301                         case ACL_USER_OBJ:
 302                                 pa->e_perm &= (mode >> 6) | ~S_IRWXO;
 303                                 mode &= (pa->e_perm << 6) | ~S_IRWXU;
 304                                 break;
 305
 306                         case ACL_USER:
 307                         case ACL_GROUP:
 308                                 not_equiv = 1;
 309                                 break;
 310
 311                         case ACL_GROUP_OBJ:
 312                                 group_obj = pa;
 313                                 break;
 314
 315                         case ACL_OTHER:
 316                                 pa->e_perm &= mode | ~S_IRWXO;
 317                                 mode &= pa->e_perm | ~S_IRWXO;
 318                                 break;
 319
 320                         case ACL_MASK:
 321                                 mask_obj = pa;
 322                                 not_equiv = 1;
 323                                 break;
 324
 325                         default:
 326                                 return -EIO;
 327                 }
 328         }
 329
 330         if (mask_obj) {
 331                 mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 332                 mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
 333         } else {
 334                 if (!group_obj)
 335                         return -EIO;
 336                 group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 337                 mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
 338         }
 339
 340         *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 341         return not_equiv;
 342 }
 343
 344 /**
 345  * posix_acl_update_mode  -  update mode in set_acl
 346  *
 347  * Update the file mode when setting an ACL: compute the new file permission
 348  * bits based on the ACL.  In addition, if the ACL is equivalent to the new
 349  * file mode, set *acl to NULL to indicate that no ACL should be set.
 350  *
 351  * As with chmod, clear the setgit bit if the caller is not in the owning group
 352  * or capable of CAP_FSETID (see inode_change_ok).
 353  *
 354  * Called from set_acl inode operations.
 355  */
 356 int posix_acl_update_mode(struct inode *inode, umode_t *mode_p,
 357                           struct posix_acl **acl)
 358 {
 359         umode_t mode = inode->i_mode;
 360         int error;
 361
 362         error = posix_acl_equiv_mode(*acl, &mode);
 363         if (error < 0)
 364                 return error;
 365         if (error == 0)
 366                 *acl = NULL;
 367         if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
 368                 mode &= ~S_ISGID;
 369         *mode_p = mode;
 370         return 0;
 371 }
 372 EXPORT_SYMBOL(posix_acl_update_mode);
 373
 374 /*
 375  * Modify the ACL for the chmod syscall.
 376  */
 377 static int posix_acl_chmod_masq(struct posix_acl *acl, umode_t mode)
 378 {
 379         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 380         struct posix_acl_entry *pa, *pe;
 381
 382         /* assert(atomic_read(acl->a_refcount) == 1); */
 383
 384         FOREACH_ACL_ENTRY(pa, acl, pe) {
 385                 switch(pa->e_tag) {
 386                         case ACL_USER_OBJ:
 387                                 pa->e_perm = (mode & S_IRWXU) >> 6;
 388                                 break;
 389
 390                         case ACL_USER:
 391                         case ACL_GROUP:
 392                                 break;
 393
 394                         case ACL_GROUP_OBJ:
 395                                 group_obj = pa;
 396                                 break;
 397
 398                         case ACL_MASK:
 399                                 mask_obj = pa;
 400                                 break;
 401
 402                         case ACL_OTHER:
 403                                 pa->e_perm = (mode & S_IRWXO);
 404                                 break;
 405
 406                         default:
 407                                 return -EIO;
 408                 }
 409         }
 410
 411         if (mask_obj) {
 412                 mask_obj->e_perm = (mode & S_IRWXG) >> 3;
 413         } else {
 414                 if (!group_obj)
 415                         return -EIO;
 416                 group_obj->e_perm = (mode & S_IRWXG) >> 3;
 417         }
 418
 419         return 0;
 420 }
 421
 422 int
 423 posix_acl_create(struct posix_acl **acl, gfp_t gfp, umode_t *mode_p)
 424 {
 425         struct posix_acl *clone = posix_acl_clone(*acl, gfp);
 426         int err = -ENOMEM;
 427         if (clone) {
 428                 err = posix_acl_create_masq(clone, mode_p);
 429                 if (err < 0) {
 430                         posix_acl_release(clone);
 431                         clone = NULL;
 432                 }
 433         }
 434         posix_acl_release(*acl);
 435         *acl = clone;
 436         return err;
 437 }
 438 EXPORT_SYMBOL(posix_acl_create);
 439
 440 int
 441 posix_acl_chmod(struct posix_acl **acl, gfp_t gfp, umode_t mode)
 442 {
 443         struct posix_acl *clone = posix_acl_clone(*acl, gfp);
 444         int err = -ENOMEM;
 445         if (clone) {
 446                 err = posix_acl_chmod_masq(clone, mode);
 447                 if (err) {
 448                         posix_acl_release(clone);
 449                         clone = NULL;
 450                 }
 451         }
 452         posix_acl_release(*acl);
 453         *acl = clone;
 454         return err;
 455 }
 456 EXPORT_SYMBOL(posix_acl_chmod);