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/export.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         FOREACH_ACL_ENTRY(pa, acl, pe) {
 159                 switch (pa->e_tag) {
 160                         case ACL_USER_OBJ:
 161                                 mode |= (pa->e_perm & S_IRWXO) << 6;
 162                                 break;
 163                         case ACL_GROUP_OBJ:
 164                                 mode |= (pa->e_perm & S_IRWXO) << 3;
 165                                 break;
 166                         case ACL_OTHER:
 167                                 mode |= pa->e_perm & S_IRWXO;
 168                                 break;
 169                         case ACL_MASK:
 170                                 mode = (mode & ~S_IRWXG) |
 171                                        ((pa->e_perm & S_IRWXO) << 3);
 172                                 not_equiv = 1;
 173                                 break;
 174                         case ACL_USER:
 175                         case ACL_GROUP:
 176                                 not_equiv = 1;
 177                                 break;
 178                         default:
 179                                 return -EINVAL;
 180                 }
 181         }
 182         if (mode_p)
 183                 *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 184         return not_equiv;
 185 }
 186
 187 /*
 188  * Create an ACL representing the file mode permission bits of an inode.
 189  */
 190 struct posix_acl *
 191 posix_acl_from_mode(umode_t mode, gfp_t flags)
 192 {
 193         struct posix_acl *acl = posix_acl_alloc(3, flags);
 194         if (!acl)
 195                 return ERR_PTR(-ENOMEM);
 196
 197         acl->a_entries[0].e_tag  = ACL_USER_OBJ;
 198         acl->a_entries[0].e_id   = ACL_UNDEFINED_ID;
 199         acl->a_entries[0].e_perm = (mode & S_IRWXU) >> 6;
 200
 201         acl->a_entries[1].e_tag  = ACL_GROUP_OBJ;
 202         acl->a_entries[1].e_id   = ACL_UNDEFINED_ID;
 203         acl->a_entries[1].e_perm = (mode & S_IRWXG) >> 3;
 204
 205         acl->a_entries[2].e_tag  = ACL_OTHER;
 206         acl->a_entries[2].e_id   = ACL_UNDEFINED_ID;
 207         acl->a_entries[2].e_perm = (mode & S_IRWXO);
 208         return acl;
 209 }
 210
 211 /*
 212  * Return 0 if current is granted want access to the inode
 213  * by the acl. Returns -E... otherwise.
 214  */
 215 int
 216 posix_acl_permission(struct inode *inode, const struct posix_acl *acl, int want)
 217 {
 218         const struct posix_acl_entry *pa, *pe, *mask_obj;
 219         int found = 0;
 220
 221         want &= MAY_READ | MAY_WRITE | MAY_EXEC | MAY_NOT_BLOCK;
 222
 223         FOREACH_ACL_ENTRY(pa, acl, pe) {
 224                 switch(pa->e_tag) {
 225                         case ACL_USER_OBJ:
 226                                 /* (May have been checked already) */
 227                                 if (inode->i_uid == current_fsuid())
 228                                         goto check_perm;
 229                                 break;
 230                         case ACL_USER:
 231                                 if (pa->e_id == current_fsuid())
 232                                         goto mask;
 233                                 break;
 234                         case ACL_GROUP_OBJ:
 235                                 if (in_group_p(inode->i_gid)) {
 236                                         found = 1;
 237                                         if ((pa->e_perm & want) == want)
 238                                                 goto mask;
 239                                 }
 240                                 break;
 241                         case ACL_GROUP:
 242                                 if (in_group_p(pa->e_id)) {
 243                                         found = 1;
 244                                         if ((pa->e_perm & want) == want)
 245                                                 goto mask;
 246                                 }
 247                                 break;
 248                         case ACL_MASK:
 249                                 break;
 250                         case ACL_OTHER:
 251                                 if (found)
 252                                         return -EACCES;
 253                                 else
 254                                         goto check_perm;
 255                         default:
 256                                 return -EIO;
 257                 }
 258         }
 259         return -EIO;
 260
 261 mask:
 262         for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
 263                 if (mask_obj->e_tag == ACL_MASK) {
 264                         if ((pa->e_perm & mask_obj->e_perm & want) == want)
 265                                 return 0;
 266                         return -EACCES;
 267                 }
 268         }
 269
 270 check_perm:
 271         if ((pa->e_perm & want) == want)
 272                 return 0;
 273         return -EACCES;
 274 }
 275
 276 /*
 277  * Modify acl when creating a new inode. The caller must ensure the acl is
 278  * only referenced once.
 279  *
 280  * mode_p initially must contain the mode parameter to the open() / creat()
 281  * system calls. All permissions that are not granted by the acl are removed.
 282  * The permissions in the acl are changed to reflect the mode_p parameter.
 283  */
 284 static int posix_acl_create_masq(struct posix_acl *acl, umode_t *mode_p)
 285 {
 286         struct posix_acl_entry *pa, *pe;
 287         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 288         umode_t mode = *mode_p;
 289         int not_equiv = 0;
 290
 291         /* assert(atomic_read(acl->a_refcount) == 1); */
 292
 293         FOREACH_ACL_ENTRY(pa, acl, pe) {
 294                 switch(pa->e_tag) {
 295                         case ACL_USER_OBJ:
 296                                 pa->e_perm &= (mode >> 6) | ~S_IRWXO;
 297                                 mode &= (pa->e_perm << 6) | ~S_IRWXU;
 298                                 break;
 299
 300                         case ACL_USER:
 301                         case ACL_GROUP:
 302                                 not_equiv = 1;
 303                                 break;
 304
 305                         case ACL_GROUP_OBJ:
 306                                 group_obj = pa;
 307                                 break;
 308
 309                         case ACL_OTHER:
 310                                 pa->e_perm &= mode | ~S_IRWXO;
 311                                 mode &= pa->e_perm | ~S_IRWXO;
 312                                 break;
 313
 314                         case ACL_MASK:
 315                                 mask_obj = pa;
 316                                 not_equiv = 1;
 317                                 break;
 318
 319                         default:
 320                                 return -EIO;
 321                 }
 322         }
 323
 324         if (mask_obj) {
 325                 mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 326                 mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
 327         } else {
 328                 if (!group_obj)
 329                         return -EIO;
 330                 group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 331                 mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
 332         }
 333
 334         *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 335         return not_equiv;
 336 }
 337
 338 /*
 339  * Modify the ACL for the chmod syscall.
 340  */
 341 static int posix_acl_chmod_masq(struct posix_acl *acl, umode_t mode)
 342 {
 343         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 344         struct posix_acl_entry *pa, *pe;
 345
 346         /* assert(atomic_read(acl->a_refcount) == 1); */
 347
 348         FOREACH_ACL_ENTRY(pa, acl, pe) {
 349                 switch(pa->e_tag) {
 350                         case ACL_USER_OBJ:
 351                                 pa->e_perm = (mode & S_IRWXU) >> 6;
 352                                 break;
 353
 354                         case ACL_USER:
 355                         case ACL_GROUP:
 356                                 break;
 357
 358                         case ACL_GROUP_OBJ:
 359                                 group_obj = pa;
 360                                 break;
 361
 362                         case ACL_MASK:
 363                                 mask_obj = pa;
 364                                 break;
 365
 366                         case ACL_OTHER:
 367                                 pa->e_perm = (mode & S_IRWXO);
 368                                 break;
 369
 370                         default:
 371                                 return -EIO;
 372                 }
 373         }
 374
 375         if (mask_obj) {
 376                 mask_obj->e_perm = (mode & S_IRWXG) >> 3;
 377         } else {
 378                 if (!group_obj)
 379                         return -EIO;
 380                 group_obj->e_perm = (mode & S_IRWXG) >> 3;
 381         }
 382
 383         return 0;
 384 }
 385
 386 int
 387 posix_acl_create(struct posix_acl **acl, gfp_t gfp, umode_t *mode_p)
 388 {
 389         struct posix_acl *clone = posix_acl_clone(*acl, gfp);
 390         int err = -ENOMEM;
 391         if (clone) {
 392                 err = posix_acl_create_masq(clone, mode_p);
 393                 if (err < 0) {
 394                         posix_acl_release(clone);
 395                         clone = NULL;
 396                 }
 397         }
 398         posix_acl_release(*acl);
 399         *acl = clone;
 400         return err;
 401 }
 402 EXPORT_SYMBOL(posix_acl_create);
 403
 404 int
 405 posix_acl_chmod(struct posix_acl **acl, gfp_t gfp, umode_t mode)
 406 {
 407         struct posix_acl *clone = posix_acl_clone(*acl, gfp);
 408         int err = -ENOMEM;
 409         if (clone) {
 410                 err = posix_acl_chmod_masq(clone, mode);
 411                 if (err) {
 412                         posix_acl_release(clone);
 413                         clone = NULL;
 414                 }
 415         }
 416         posix_acl_release(*acl);
 417         *acl = clone;
 418         return err;
 419 }
 420 EXPORT_SYMBOL(posix_acl_chmod);