kernel/groups.c

   1 /*
   2  * Supplementary group IDs
   3  */
   4 #include <linux/cred.h>
   5 #include <linux/export.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                         kgid_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         struct user_namespace *user_ns = current_user_ns();
  70         int i;
  71         unsigned int count = group_info->ngroups;
  72
  73         for (i = 0; i < count; i++) {
  74                 gid_t gid;
  75                 gid = from_kgid_munged(user_ns, GROUP_AT(group_info, i));
  76                 if (put_user(gid, grouplist+i))
  77                         return -EFAULT;
  78         }
  79         return 0;
  80 }
  81
  82 /* fill a group_info from a user-space array - it must be allocated already */
  83 static int groups_from_user(struct group_info *group_info,
  84     gid_t __user *grouplist)
  85 {
  86         struct user_namespace *user_ns = current_user_ns();
  87         int i;
  88         unsigned int count = group_info->ngroups;
  89
  90         for (i = 0; i < count; i++) {
  91                 gid_t gid;
  92                 kgid_t kgid;
  93                 if (get_user(gid, grouplist+i))
  94                         return -EFAULT;
  95
  96                 kgid = make_kgid(user_ns, gid);
  97                 if (!gid_valid(kgid))
  98                         return -EINVAL;
  99
 100                 GROUP_AT(group_info, i) = kgid;
 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                         kgid_t tmp = GROUP_AT(group_info, right);
 121
 122                         while (left >= 0 && gid_gt(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, kgid_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                 if (gid_gt(grp, GROUP_AT(group_info, mid)))
 147                         left = mid + 1;
 148                 else if (gid_lt(grp, GROUP_AT(group_info, mid)))
 149                         right = mid;
 150                 else
 151                         return 1;
 152         }
 153         return 0;
 154 }
 155
 156 /**
 157  * set_groups - Change a group subscription in a set of credentials
 158  * @new: The newly prepared set of credentials to alter
 159  * @group_info: The group list to install
 160  */
 161 void set_groups(struct cred *new, struct group_info *group_info)
 162 {
 163         put_group_info(new->group_info);
 164         groups_sort(group_info);
 165         get_group_info(group_info);
 166         new->group_info = group_info;
 167 }
 168
 169 EXPORT_SYMBOL(set_groups);
 170
 171 /**
 172  * set_current_groups - Change current's group subscription
 173  * @group_info: The group list to impose
 174  *
 175  * Validate a group subscription and, if valid, impose it upon current's task
 176  * security record.
 177  */
 178 int set_current_groups(struct group_info *group_info)
 179 {
 180         struct cred *new;
 181
 182         new = prepare_creds();
 183         if (!new)
 184                 return -ENOMEM;
 185
 186         set_groups(new, group_info);
 187         return commit_creds(new);
 188 }
 189
 190 EXPORT_SYMBOL(set_current_groups);
 191
 192 SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
 193 {
 194         const struct cred *cred = current_cred();
 195         int i;
 196
 197         if (gidsetsize < 0)
 198                 return -EINVAL;
 199
 200         /* no need to grab task_lock here; it cannot change */
 201         i = cred->group_info->ngroups;
 202         if (gidsetsize) {
 203                 if (i > gidsetsize) {
 204                         i = -EINVAL;
 205                         goto out;
 206                 }
 207                 if (groups_to_user(grouplist, cred->group_info)) {
 208                         i = -EFAULT;
 209                         goto out;
 210                 }
 211         }
 212 out:
 213         return i;
 214 }
 215
 216 /*
 217  *      SMP: Our groups are copy-on-write. We can set them safely
 218  *      without another task interfering.
 219  */
 220
 221 SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
 222 {
 223         struct group_info *group_info;
 224         int retval;
 225
 226         if (!ns_capable(current_user_ns(), CAP_SETGID))
 227                 return -EPERM;
 228         if ((unsigned)gidsetsize > NGROUPS_MAX)
 229                 return -EINVAL;
 230
 231         group_info = groups_alloc(gidsetsize);
 232         if (!group_info)
 233                 return -ENOMEM;
 234         retval = groups_from_user(group_info, grouplist);
 235         if (retval) {
 236                 put_group_info(group_info);
 237                 return retval;
 238         }
 239
 240         retval = set_current_groups(group_info);
 241         put_group_info(group_info);
 242
 243         return retval;
 244 }
 245
 246 /*
 247  * Check whether we're fsgid/egid or in the supplemental group..
 248  */
 249 int in_group_p(kgid_t grp)
 250 {
 251         const struct cred *cred = current_cred();
 252         int retval = 1;
 253
 254         if (!gid_eq(grp, cred->fsgid))
 255                 retval = groups_search(cred->group_info, grp);
 256         return retval;
 257 }
 258
 259 EXPORT_SYMBOL(in_group_p);
 260
 261 int in_egroup_p(kgid_t grp)
 262 {
 263         const struct cred *cred = current_cred();
 264         int retval = 1;
 265
 266         if (!gid_eq(grp, cred->egid))
 267                 retval = groups_search(cred->group_info, grp);
 268         return retval;
 269 }
 270
 271 EXPORT_SYMBOL(in_egroup_p);