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_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, mode_t *mode_p)
 153 {
 154         const struct posix_acl_entry *pa, *pe;
 155         mode_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(mode_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         FOREACH_ACL_ENTRY(pa, acl, pe) {
 222                 switch(pa->e_tag) {
 223                         case ACL_USER_OBJ:
 224                                 /* (May have been checked already) */
 225                                 if (inode->i_uid == current_fsuid())
 226                                         goto check_perm;
 227                                 break;
 228                         case ACL_USER:
 229                                 if (pa->e_id == current_fsuid())
 230                                         goto mask;
 231                                 break;
 232                         case ACL_GROUP_OBJ:
 233                                 if (in_group_p(inode->i_gid)) {
 234                                         found = 1;
 235                                         if ((pa->e_perm & want) == want)
 236                                                 goto mask;
 237                                 }
 238                                 break;
 239                         case ACL_GROUP:
 240                                 if (in_group_p(pa->e_id)) {
 241                                         found = 1;
 242                                         if ((pa->e_perm & want) == want)
 243                                                 goto mask;
 244                                 }
 245                                 break;
 246                         case ACL_MASK:
 247                                 break;
 248                         case ACL_OTHER:
 249                                 if (found)
 250                                         return -EACCES;
 251                                 else
 252                                         goto check_perm;
 253                         default:
 254                                 return -EIO;
 255                 }
 256         }
 257         return -EIO;
 258
 259 mask:
 260         for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
 261                 if (mask_obj->e_tag == ACL_MASK) {
 262                         if ((pa->e_perm & mask_obj->e_perm & want) == want)
 263                                 return 0;
 264                         return -EACCES;
 265                 }
 266         }
 267
 268 check_perm:
 269         if ((pa->e_perm & want) == want)
 270                 return 0;
 271         return -EACCES;
 272 }
 273
 274 /*
 275  * Modify acl when creating a new inode. The caller must ensure the acl is
 276  * only referenced once.
 277  *
 278  * mode_p initially must contain the mode parameter to the open() / creat()
 279  * system calls. All permissions that are not granted by the acl are removed.
 280  * The permissions in the acl are changed to reflect the mode_p parameter.
 281  */
 282 static int posix_acl_create_masq(struct posix_acl *acl, mode_t *mode_p)
 283 {
 284         struct posix_acl_entry *pa, *pe;
 285         struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
 286         mode_t mode = *mode_p;
 287         int not_equiv = 0;
 288
 289         /* assert(atomic_read(acl->a_refcount) == 1); */
 290
 291         FOREACH_ACL_ENTRY(pa, acl, pe) {
 292                 switch(pa->e_tag) {
 293                         case ACL_USER_OBJ:
 294                                 pa->e_perm &= (mode >> 6) | ~S_IRWXO;
 295                                 mode &= (pa->e_perm << 6) | ~S_IRWXU;
 296                                 break;
 297
 298                         case ACL_USER:
 299                         case ACL_GROUP:
 300                                 not_equiv = 1;
 301                                 break;
 302
 303                         case ACL_GROUP_OBJ:
 304                                 group_obj = pa;
 305                                 break;
 306
 307                         case ACL_OTHER:
 308                                 pa->e_perm &= mode | ~S_IRWXO;
 309                                 mode &= pa->e_perm | ~S_IRWXO;
 310                                 break;
 311
 312                         case ACL_MASK:
 313                                 mask_obj = pa;
 314                                 not_equiv = 1;
 315                                 break;
 316
 317                         default:
 318                                 return -EIO;
 319                 }
 320         }
 321
 322         if (mask_obj) {
 323                 mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 324                 mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
 325         } else {
 326                 if (!group_obj)
 327                         return -EIO;
 328                 group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
 329                 mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
 330         }
 331
 332         *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
 333         return not_equiv;
 334 }
 335
 336 /*
 337  * Modify the ACL for the chmod syscall.
 338  */
 339 static int 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 int
 385 posix_acl_create(struct posix_acl **acl, gfp_t gfp, mode_t *mode_p)
 386 {
 387         struct posix_acl *clone = posix_acl_clone(*acl, gfp);
 388         int err = -ENOMEM;
 389         if (clone) {
 390                 err = posix_acl_create_masq(clone, mode_p);
 391                 if (err < 0) {
 392                         posix_acl_release(clone);
 393                         clone = NULL;
 394                 }
 395         }
 396         posix_acl_release(*acl);
 397         *acl = clone;
 398         return err;
 399 }
 400 EXPORT_SYMBOL(posix_acl_create);
 401
 402 int
 403 posix_acl_chmod(struct posix_acl **acl, gfp_t gfp, mode_t mode)
 404 {
 405         struct posix_acl *clone = posix_acl_clone(*acl, gfp);
 406         int err = -ENOMEM;
 407         if (clone) {
 408                 err = posix_acl_chmod_masq(clone, mode);
 409                 if (err) {
 410                         posix_acl_release(clone);
 411                         clone = NULL;
 412                 }
 413         }
 414         posix_acl_release(*acl);
 415         *acl = clone;
 416         return err;
 417 }
 418 EXPORT_SYMBOL(posix_acl_chmod);