kernel/groups.c

   1 /*
   2  * Supplementary group IDs
   3  */
   4 #include <linux/cred.h>
   5 #include <linux/module.h>
   6 #include <linux/slab.h>
   7 #include <linux/security.h>
   8 #include <linux/syscalls.h>
   9 #include <asm/uaccess.h>
  10
  11 /* init to 2 - one for init_task, one to ensure it is never freed */
  12 struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
  13
  14 struct group_info *groups_alloc(int gidsetsize)
  15 {
  16         struct group_info *group_info;
  17         int nblocks;
  18         int i;
  19
  20         nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;
  21         /* Make sure we always allocate at least one indirect block pointer */
  22         nblocks = nblocks ? : 1;
  23         group_info = kmalloc(sizeof(*group_info) + nblocks*sizeof(gid_t *), GFP_USER);
  24         if (!group_info)
  25                 return NULL;
  26         group_info->ngroups = gidsetsize;
  27         group_info->nblocks = nblocks;
  28         atomic_set(&group_info->usage, 1);
  29
  30         if (gidsetsize <= NGROUPS_SMALL)
  31                 group_info->blocks[0] = group_info->small_block;
  32         else {
  33                 for (i = 0; i < nblocks; i++) {
  34                         gid_t *b;
  35                         b = (void *)__get_free_page(GFP_USER);
  36                         if (!b)
  37                                 goto out_undo_partial_alloc;
  38                         group_info->blocks[i] = b;
  39                 }
  40         }
  41         return group_info;
  42
  43 out_undo_partial_alloc:
  44         while (--i >= 0) {
  45                 free_page((unsigned long)group_info->blocks[i]);
  46         }
  47         kfree(group_info);
  48         return NULL;
  49 }
  50
  51 EXPORT_SYMBOL(groups_alloc);
  52
  53 void groups_free(struct group_info *group_info)
  54 {
  55         if (group_info->blocks[0] != group_info->small_block) {
  56                 int i;
  57                 for (i = 0; i < group_info->nblocks; i++)
  58                         free_page((unsigned long)group_info->blocks[i]);
  59         }
  60         kfree(group_info);
  61 }
  62
  63 EXPORT_SYMBOL(groups_free);
  64
  65 /* export the group_info to a user-space array */
  66 static int groups_to_user(gid_t __user *grouplist,
  67                           const struct group_info *group_info)
  68 {
  69         int i;
  70         unsigned int count = group_info->ngroups;
  71
  72         for (i = 0; i < group_info->nblocks; i++) {
  73                 unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);
  74                 unsigned int len = cp_count * sizeof(*grouplist);
  75
  76                 if (copy_to_user(grouplist, group_info->blocks[i], len))
  77                         return -EFAULT;
  78
  79                 grouplist += NGROUPS_PER_BLOCK;
  80                 count -= cp_count;
  81         }
  82         return 0;
  83 }
  84
  85 /* fill a group_info from a user-space array - it must be allocated already */
  86 static int groups_from_user(struct group_info *group_info,
  87     gid_t __user *grouplist)
  88 {
  89         int i;
  90         unsigned int count = group_info->ngroups;
  91
  92         for (i = 0; i < group_info->nblocks; i++) {
  93                 unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);
  94                 unsigned int len = cp_count * sizeof(*grouplist);
  95
  96                 if (copy_from_user(group_info->blocks[i], grouplist, len))
  97                         return -EFAULT;
  98
  99                 grouplist += NGROUPS_PER_BLOCK;
 100                 count -= cp_count;
 101         }
 102         return 0;
 103 }
 104
 105 /* a simple Shell sort */
 106 static void groups_sort(struct group_info *group_info)
 107 {
 108         int base, max, stride;
 109         int gidsetsize = group_info->ngroups;
 110
 111         for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1)
 112                 ; /* nothing */
 113         stride /= 3;
 114
 115         while (stride) {
 116                 max = gidsetsize - stride;
 117                 for (base = 0; base < max; base++) {
 118                         int left = base;
 119                         int right = left + stride;
 120                         gid_t tmp = GROUP_AT(group_info, right);
 121
 122                         while (left >= 0 && GROUP_AT(group_info, left) > tmp) {
 123                                 GROUP_AT(group_info, right) =
 124                                     GROUP_AT(group_info, left);
 125                                 right = left;
 126                                 left -= stride;
 127                         }
 128                         GROUP_AT(group_info, right) = tmp;
 129                 }
 130                 stride /= 3;
 131         }
 132 }
 133
 134 /* a simple bsearch */
 135 int groups_search(const struct group_info *group_info, gid_t grp)
 136 {
 137         unsigned int left, right;
 138
 139         if (!group_info)
 140                 return 0;
 141
 142         left = 0;
 143         right = group_info->ngroups;
 144         while (left < right) {
 145                 unsigned int mid = (left+right)/2;
 146                 int cmp = grp - GROUP_AT(group_info, mid);
 147                 if (cmp > 0)
 148                         left = mid + 1;
 149                 else if (cmp < 0)
 150                         right = mid;
 151                 else
 152                         return 1;
 153         }
 154         return 0;
 155 }
 156
 157 /**
 158  * set_groups - Change a group subscription in a set of credentials
 159  * @new: The newly prepared set of credentials to alter
 160  * @group_info: The group list to install
 161  *
 162  * Validate a group subscription and, if valid, insert it into a set
 163  * of credentials.
 164  */
 165 int set_groups(struct cred *new, struct group_info *group_info)
 166 {
 167         int retval;
 168
 169         retval = security_task_setgroups(group_info);
 170         if (retval)
 171                 return retval;
 172
 173         put_group_info(new->group_info);
 174         groups_sort(group_info);
 175         get_group_info(group_info);
 176         new->group_info = group_info;
 177         return 0;
 178 }
 179
 180 EXPORT_SYMBOL(set_groups);
 181
 182 /**
 183  * set_current_groups - Change current's group subscription
 184  * @group_info: The group list to impose
 185  *
 186  * Validate a group subscription and, if valid, impose it upon current's task
 187  * security record.
 188  */
 189 int set_current_groups(struct group_info *group_info)
 190 {
 191         struct cred *new;
 192         int ret;
 193
 194         new = prepare_creds();
 195         if (!new)
 196                 return -ENOMEM;
 197
 198         ret = set_groups(new, group_info);
 199         if (ret < 0) {
 200                 abort_creds(new);
 201                 return ret;
 202         }
 203
 204         return commit_creds(new);
 205 }
 206
 207 EXPORT_SYMBOL(set_current_groups);
 208
 209 SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
 210 {
 211         const struct cred *cred = current_cred();
 212         int i;
 213
 214         if (gidsetsize < 0)
 215                 return -EINVAL;
 216
 217         /* no need to grab task_lock here; it cannot change */
 218         i = cred->group_info->ngroups;
 219         if (gidsetsize) {
 220                 if (i > gidsetsize) {
 221                         i = -EINVAL;
 222                         goto out;
 223                 }
 224                 if (groups_to_user(grouplist, cred->group_info)) {
 225                         i = -EFAULT;
 226                         goto out;
 227                 }
 228         }
 229 out:
 230         return i;
 231 }
 232
 233 /*
 234  *      SMP: Our groups are copy-on-write. We can set them safely
 235  *      without another task interfering.
 236  */
 237
 238 SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
 239 {
 240         struct group_info *group_info;
 241         int retval;
 242
 243         if (!capable(CAP_SETGID))
 244                 return -EPERM;
 245         if ((unsigned)gidsetsize > NGROUPS_MAX)
 246                 return -EINVAL;
 247
 248         group_info = groups_alloc(gidsetsize);
 249         if (!group_info)
 250                 return -ENOMEM;
 251         retval = groups_from_user(group_info, grouplist);
 252         if (retval) {
 253                 put_group_info(group_info);
 254                 return retval;
 255         }
 256
 257         retval = set_current_groups(group_info);
 258         put_group_info(group_info);
 259
 260         return retval;
 261 }
 262
 263 /*
 264  * Check whether we're fsgid/egid or in the supplemental group..
 265  */
 266 int in_group_p(gid_t grp)
 267 {
 268         const struct cred *cred = current_cred();
 269         int retval = 1;
 270
 271         if (grp != cred->fsgid)
 272                 retval = groups_search(cred->group_info, grp);
 273         return retval;
 274 }
 275
 276 EXPORT_SYMBOL(in_group_p);
 277
 278 int in_egroup_p(gid_t grp)
 279 {
 280         const struct cred *cred = current_cred();
 281         int retval = 1;
 282
 283         if (grp != cred->egid)
 284                 retval = groups_search(cred->group_info, grp);
 285         return retval;
 286 }
 287
 288 EXPORT_SYMBOL(in_egroup_p);