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 <asm/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_alloc);
  26 EXPORT_SYMBOL(posix_acl_clone);
  27 EXPORT_SYMBOL(posix_acl_valid);
  28 EXPORT_SYMBOL(posix_acl_equiv_mode);
  29 EXPORT_SYMBOL(posix_acl_from_mode);
  30 EXPORT_SYMBOL(posix_acl_create_masq);
  31 EXPORT_SYMBOL(posix_acl_chmod_masq);
  32 EXPORT_SYMBOL(posix_acl_masq_nfs_mode);
  33 EXPORT_SYMBOL(posix_acl_permission);
  34
  35 /*
  36  * Allocate a new ACL with the specified number of entries.
  37  */
  38 struct posix_acl *
  39 posix_acl_alloc(int count, int flags)
  40 {
  41         const size_t size = sizeof(struct posix_acl) +
  42                             count * sizeof(struct posix_acl_entry);
  43         struct posix_acl *acl = kmalloc(size, flags);
  44         if (acl) {
  45                 atomic_set(&acl->a_refcount, 1);
  46                 acl->a_count = count;
  47         }
  48         return acl;
  49 }
  50
  51 /*
  52  * Clone an ACL.
  53  */
  54 struct posix_acl *
  55 posix_acl_clone(const struct posix_acl *acl, int flags)
  56 {
  57         struct posix_acl *clone = NULL;
  58
  59         if (acl) {
  60                 int size = sizeof(struct posix_acl) + acl->a_count *
  61                            sizeof(struct posix_acl_entry);
  62                 clone = kmalloc(size, flags);
  63                 if (clone) {
  64                         memcpy(clone, acl, size);
  65                         atomic_set(&clone->a_refcount, 1);
  66                 }
  67         }
  68         return clone;
  69 }
  70
  71 /*
  72  * Check if an acl is valid. Returns 0 if it is, or -E... otherwise.
  73  */
  74 int
  75 posix_acl_valid(const struct posix_acl *acl)
  76 {
  77         const struct posix_acl_entry *pa, *pe;
  78         int state = ACL_USER_OBJ;
  79         unsigned int id = 0;  /* keep gcc happy */
  80         int needs_mask = 0;
  81
  82         FOREACH_ACL_ENTRY(pa, acl, pe) {
  83                 if (pa->e_perm & ~(ACL_READ|ACL_WRITE|ACL_EXECUTE))
  84                         return -EINVAL;
  85                 switch (pa->e_tag) {
  86                         case ACL_USER_OBJ:
  87                                 if (state == ACL_USER_OBJ) {
  88                                         id = 0;
  89                                         state = ACL_USER;
  90                                         break;
  91                                 }
  92                                 return -EINVAL;
  93
  94                         case ACL_USER:
  95                                 if (state != ACL_USER)
  96                                         return -EINVAL;
  97                                 if (pa->e_id == ACL_UNDEFINED_ID ||
  98                                     pa->e_id < id)
  99                                         return -EINVAL;
 100                                 id = pa->e_id + 1;
 101                                 needs_mask = 1;
 102                                 break;
 103
 104                         case ACL_GROUP_OBJ:
 105                                 if (state == ACL_USER) {
 106                                         id = 0;
 107                                         state = ACL_GROUP;
 108                                         break;
 109                                 }
 110                                 return -EINVAL;
 111
 112                         case ACL_GROUP:
 113                                 if (state != ACL_GROUP)
 114                                         return -EINVAL;
 115                                 if (pa->e_id == ACL_UNDEFINED_ID ||
 116                                     pa->e_id < id)
 117                                         return -EINVAL;
 118                                 id = pa->e_id + 1;
 119                                 needs_mask = 1;
 120                                 break;
 121
 122                         case ACL_MASK:
 123                                 if (state != ACL_GROUP)
 124                                         return -EINVAL;
 125                                 state = ACL_OTHER;
 126                                 break;
 127
 128                         case ACL_OTHER:
 129                                 if (state == ACL_OTHER ||
 130                                     (state == ACL_GROUP && !needs_mask)) {
 131                                         state = 0;
 132                                         break;
 133                                 }
 134                                 return -EINVAL;
 135
 136                         default:
 137                                 return -EINVAL;
 138                 }
 139         }
 140         if (state == 0)
 141                 return 0;
 142         return -EINVAL;
 143 }
 144
 145 /*
 146  * Returns 0 if the acl can be exactly represented in the traditional
 147  * file mode permission bits, or else 1. Returns -E... on error.
 148  */
 149 int
 150 posix_acl_equiv_mode(const struct posix_acl *acl, mode_t *mode_p)
 151 {
 152         const struct posix_acl_entry *pa, *pe;
 153         mode_t mode = 0;
 154         int not_equiv = 0;
 155
 156         FOREACH_ACL_ENTRY(pa, acl, pe) {
 157                 switch (pa->e_tag) {
 158                         case ACL_USER_OBJ:
 159                                 mode |= (pa->e_perm & S_IRWXO) << 6;
 160                                 break;
 161                         case ACL_GROUP_OBJ:
 162                                 mode |= (pa->e_perm & S_IRWXO) << 3;
 163                                 break;
 164                         case ACL_OTHER:
 165                                 mode |= pa->e_perm & S_IRWXO;
 166                                 break;
 167                         case ACL_MASK:
 168                                 mode = (mode & ~S_IRWXG) |
 169                                        ((pa->e_perm & S_IRWXO) << 3);
 170                                 not_equiv = 1;
 171                                 break;
 172                         case ACL_USER:
 173                         case ACL_GROUP:
 174                                 not_equiv = 1;
 175                                 break;
 176                         default:
 177                                 return -EINVAL;
 178                 }
 179         }
 180         if (mode_p)
 181                 *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 182         return not_equiv;
 183 }
 184
 185 /*
 186  * Create an ACL representing the file mode permission bits of an inode.
 187  */
 188 struct posix_acl *
 189 posix_acl_from_mode(mode_t mode, int flags)
 190 {
 191         struct posix_acl *acl = posix_acl_alloc(3, flags);
 192         if (!acl)
 193                 return ERR_PTR(-ENOMEM);
 194
 195         acl->a_entries[0].e_tag  = ACL_USER_OBJ;
 196         acl->a_entries[0].e_id   = ACL_UNDEFINED_ID;
 197         acl->a_entries[0].e_perm = (mode & S_IRWXU) >> 6;
 198
 199         acl->a_entries[1].e_tag  = ACL_GROUP_OBJ;
 200         acl->a_entries[1].e_id   = ACL_UNDEFINED_ID;
 201         acl->a_entries[1].e_perm = (mode & S_IRWXG) >> 3;
 202
 203         acl->a_entries[2].e_tag  = ACL_OTHER;
 204         acl->a_entries[2].e_id   = ACL_UNDEFINED_ID;
 205         acl->a_entries[2].e_perm = (mode & S_IRWXO);
 206         return acl;
 207 }
 208
 209 /*
 210  * Return 0 if current is granted want access to the inode
 211  * by the acl. Returns -E... otherwise.
 212  */
 213 int
 214 posix_acl_permission(struct inode *inode, const struct posix_acl *acl, int want)
 215 {
 216         const struct posix_acl_entry *pa, *pe, *mask_obj;
 217         int found = 0;
 218
 219         FOREACH_ACL_ENTRY(pa, acl, pe) {
 220                 switch(pa->e_tag) {
 221                         case ACL_USER_OBJ:
 222                                 /* (May have been checked already) */
 223                                 if (inode->i_uid == current->fsuid)
 224                                         goto check_perm;
 225                                 break;
 226                         case ACL_USER:
 227                                 if (pa->e_id == current->fsuid)
 228                                         goto mask;
 229                                 break;
 230                         case ACL_GROUP_OBJ:
 231                                 if (in_group_p(inode->i_gid)) {
 232                                         found = 1;
 233                                         if ((pa->e_perm & want) == want)
 234                                                 goto mask;
 235                                 }
 236                                 break;
 237                         case ACL_GROUP:
 238                                 if (in_group_p(pa->e_id)) {
 239                                         found = 1;
 240                                         if ((pa->e_perm & want) == want)
 241                                                 goto mask;
 242                                 }
 243                                 break;
 244                         case ACL_MASK:
 245                                 break;
 246                         case ACL_OTHER:
 247                                 if (found)
 248                                         return -EACCES;
 249                                 else
 250                                         goto check_perm;
 251                         default:
 252                                 return -EIO;
 253                 }
 254         }
 255         return -EIO;
 256
 257 mask:
 258         for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
 259                 if (mask_obj->e_tag == ACL_MASK) {
 260                         if ((pa->e_perm & mask_obj->e_perm & want) == want)
 261                                 return 0;
 262                         return -EACCES;
 263                 }
 264         }
 265
 266 check_perm:
 267         if ((pa->e_perm & want) == want)
 268                 return 0;
 269         return -EACCES;
 270 }
 271
 272 /*
 273  * Modify acl when creating a new inode. The caller must ensure the acl is
 274  * only referenced once.
 275  *
 276  * mode_p initially must contain the mode parameter to the open() / creat()
 277  * system calls. All permissions that are not granted by the acl are removed.
 278  * The permissions in the acl are changed to reflect the mode_p parameter.
 279  */
 280 int
 281 posix_acl_create_masq(struct posix_acl *acl, mode_t *mode_p)
 282 {
 283         struct posix_acl_entry *pa, *pe;
 284         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 285         mode_t mode = *mode_p;
 286         int not_equiv = 0;
 287
 288         /* assert(atomic_read(acl->a_refcount) == 1); */
 289
 290         FOREACH_ACL_ENTRY(pa, acl, pe) {
 291                 switch(pa->e_tag) {
 292                         case ACL_USER_OBJ:
 293                                 pa->e_perm &= (mode >> 6) | ~S_IRWXO;
 294                                 mode &= (pa->e_perm << 6) | ~S_IRWXU;
 295                                 break;
 296
 297                         case ACL_USER:
 298                         case ACL_GROUP:
 299                                 not_equiv = 1;
 300                                 break;
 301
 302                         case ACL_GROUP_OBJ:
 303                                 group_obj = pa;
 304                                 break;
 305
 306                         case ACL_OTHER:
 307                                 pa->e_perm &= mode | ~S_IRWXO;
 308                                 mode &= pa->e_perm | ~S_IRWXO;
 309                                 break;
 310
 311                         case ACL_MASK:
 312                                 mask_obj = pa;
 313                                 not_equiv = 1;
 314                                 break;
 315
 316                         default:
 317                                 return -EIO;
 318                 }
 319         }
 320
 321         if (mask_obj) {
 322                 mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 323                 mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
 324         } else {
 325                 if (!group_obj)
 326                         return -EIO;
 327                 group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 328                 mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
 329         }
 330
 331         *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 332         return not_equiv;
 333 }
 334
 335 /*
 336  * Modify the ACL for the chmod syscall.
 337  */
 338 int
 339 posix_acl_chmod_masq(struct posix_acl *acl, mode_t mode)
 340 {
 341         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 342         struct posix_acl_entry *pa, *pe;
 343
 344         /* assert(atomic_read(acl->a_refcount) == 1); */
 345
 346         FOREACH_ACL_ENTRY(pa, acl, pe) {
 347                 switch(pa->e_tag) {
 348                         case ACL_USER_OBJ:
 349                                 pa->e_perm = (mode & S_IRWXU) >> 6;
 350                                 break;
 351
 352                         case ACL_USER:
 353                         case ACL_GROUP:
 354                                 break;
 355
 356                         case ACL_GROUP_OBJ:
 357                                 group_obj = pa;
 358                                 break;
 359
 360                         case ACL_MASK:
 361                                 mask_obj = pa;
 362                                 break;
 363
 364                         case ACL_OTHER:
 365                                 pa->e_perm = (mode & S_IRWXO);
 366                                 break;
 367
 368                         default:
 369                                 return -EIO;
 370                 }
 371         }
 372
 373         if (mask_obj) {
 374                 mask_obj->e_perm = (mode & S_IRWXG) >> 3;
 375         } else {
 376                 if (!group_obj)
 377                         return -EIO;
 378                 group_obj->e_perm = (mode & S_IRWXG) >> 3;
 379         }
 380
 381         return 0;
 382 }
 383
 384 /*
 385  * Adjust the mode parameter so that NFSv2 grants nobody permissions
 386  * that may not be granted by the ACL. This is necessary because NFSv2
 387  * may compute access permissions on the client side, and may serve cached
 388  * data whenever it assumes access would be granted.  Since ACLs may also
 389  * be used to deny access to specific users, the minimal permissions
 390  * for secure operation over NFSv2 are very restrictive. Permissions
 391  * granted to users via Access Control Lists will not be effective over
 392  * NFSv2.
 393  *
 394  * Privilege escalation can only happen for read operations, as writes are
 395  * always carried out on the NFS server, where the proper access checks are
 396  * implemented.
 397  */
 398 int
 399 posix_acl_masq_nfs_mode(struct posix_acl *acl, mode_t *mode_p)
 400 {
 401         struct posix_acl_entry *pa, *pe; int min_perm = S_IRWXO;
 402
 403         FOREACH_ACL_ENTRY(pa, acl, pe) {
 404                 switch(pa->e_tag) {
 405                         case ACL_USER_OBJ:
 406                                 break;
 407
 408                         case ACL_USER:
 409                         case ACL_GROUP_OBJ:
 410                         case ACL_GROUP:
 411                         case ACL_MASK:
 412                         case ACL_OTHER:
 413                                 min_perm &= pa->e_perm;
 414                                 break;
 415
 416                         default:
 417                                 return -EIO;
 418                 }
 419         }
 420         *mode_p = (*mode_p & ~(S_IRWXG|S_IRWXO)) | (min_perm << 3) | min_perm;
 421
 422         return 0;
 423 }