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 <linux/user_namespace.h>
  10 #include <asm/uaccess.h>
  11
  12 struct group_info *groups_alloc(int gidsetsize)
  13 {
  14         struct group_info *group_info;
  15         int nblocks;
  16         int i;
  17
  18         nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;
  19         /* Make sure we always allocate at least one indirect block pointer */
  20         nblocks = nblocks ? : 1;
  21         group_info = kmalloc(sizeof(*group_info) + nblocks*sizeof(gid_t *), GFP_USER);
  22         if (!group_info)
  23                 return NULL;
  24         group_info->ngroups = gidsetsize;
  25         group_info->nblocks = nblocks;
  26         atomic_set(&group_info->usage, 1);
  27
  28         if (gidsetsize <= NGROUPS_SMALL)
  29                 group_info->blocks[0] = group_info->small_block;
  30         else {
  31                 for (i = 0; i < nblocks; i++) {
  32                         kgid_t *b;
  33                         b = (void *)__get_free_page(GFP_USER);
  34                         if (!b)
  35                                 goto out_undo_partial_alloc;
  36                         group_info->blocks[i] = b;
  37                 }
  38         }
  39         return group_info;
  40
  41 out_undo_partial_alloc:
  42         while (--i >= 0) {
  43                 free_page((unsigned long)group_info->blocks[i]);
  44         }
  45         kfree(group_info);
  46         return NULL;
  47 }
  48
  49 EXPORT_SYMBOL(groups_alloc);
  50
  51 void groups_free(struct group_info *group_info)
  52 {
  53         if (group_info->blocks[0] != group_info->small_block) {
  54                 int i;
  55                 for (i = 0; i < group_info->nblocks; i++)
  56                         free_page((unsigned long)group_info->blocks[i]);
  57         }
  58         kfree(group_info);
  59 }
  60
  61 EXPORT_SYMBOL(groups_free);
  62
  63 /* export the group_info to a user-space array */
  64 static int groups_to_user(gid_t __user *grouplist,
  65                           const struct group_info *group_info)
  66 {
  67         struct user_namespace *user_ns = current_user_ns();
  68         int i;
  69         unsigned int count = group_info->ngroups;
  70
  71         for (i = 0; i < count; i++) {
  72                 gid_t gid;
  73                 gid = from_kgid_munged(user_ns, GROUP_AT(group_info, i));
  74                 if (put_user(gid, grouplist+i))
  75                         return -EFAULT;
  76         }
  77         return 0;
  78 }
  79
  80 /* fill a group_info from a user-space array - it must be allocated already */
  81 static int groups_from_user(struct group_info *group_info,
  82     gid_t __user *grouplist)
  83 {
  84         struct user_namespace *user_ns = current_user_ns();
  85         int i;
  86         unsigned int count = group_info->ngroups;
  87
  88         for (i = 0; i < count; i++) {
  89                 gid_t gid;
  90                 kgid_t kgid;
  91                 if (get_user(gid, grouplist+i))
  92                         return -EFAULT;
  93
  94                 kgid = make_kgid(user_ns, gid);
  95                 if (!gid_valid(kgid))
  96                         return -EINVAL;
  97
  98                 GROUP_AT(group_info, i) = kgid;
  99         }
 100         return 0;
 101 }
 102
 103 /* a simple Shell sort */
 104 static void groups_sort(struct group_info *group_info)
 105 {
 106         int base, max, stride;
 107         int gidsetsize = group_info->ngroups;
 108
 109         for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1)
 110                 ; /* nothing */
 111         stride /= 3;
 112
 113         while (stride) {
 114                 max = gidsetsize - stride;
 115                 for (base = 0; base < max; base++) {
 116                         int left = base;
 117                         int right = left + stride;
 118                         kgid_t tmp = GROUP_AT(group_info, right);
 119
 120                         while (left >= 0 && gid_gt(GROUP_AT(group_info, left), tmp)) {
 121                                 GROUP_AT(group_info, right) =
 122                                     GROUP_AT(group_info, left);
 123                                 right = left;
 124                                 left -= stride;
 125                         }
 126                         GROUP_AT(group_info, right) = tmp;
 127                 }
 128                 stride /= 3;
 129         }
 130 }
 131
 132 /* a simple bsearch */
 133 int groups_search(const struct group_info *group_info, kgid_t grp)
 134 {
 135         unsigned int left, right;
 136
 137         if (!group_info)
 138                 return 0;
 139
 140         left = 0;
 141         right = group_info->ngroups;
 142         while (left < right) {
 143                 unsigned int mid = (left+right)/2;
 144                 if (gid_gt(grp, GROUP_AT(group_info, mid)))
 145                         left = mid + 1;
 146                 else if (gid_lt(grp, GROUP_AT(group_info, mid)))
 147                         right = mid;
 148                 else
 149                         return 1;
 150         }
 151         return 0;
 152 }
 153
 154 /**
 155  * set_groups - Change a group subscription in a set of credentials
 156  * @new: The newly prepared set of credentials to alter
 157  * @group_info: The group list to install
 158  */
 159 void set_groups(struct cred *new, struct group_info *group_info)
 160 {
 161         put_group_info(new->group_info);
 162         groups_sort(group_info);
 163         get_group_info(group_info);
 164         new->group_info = group_info;
 165 }
 166
 167 EXPORT_SYMBOL(set_groups);
 168
 169 /**
 170  * set_current_groups - Change current's group subscription
 171  * @group_info: The group list to impose
 172  *
 173  * Validate a group subscription and, if valid, impose it upon current's task
 174  * security record.
 175  */
 176 int set_current_groups(struct group_info *group_info)
 177 {
 178         struct cred *new;
 179
 180         new = prepare_creds();
 181         if (!new)
 182                 return -ENOMEM;
 183
 184         set_groups(new, group_info);
 185         return commit_creds(new);
 186 }
 187
 188 EXPORT_SYMBOL(set_current_groups);
 189
 190 SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
 191 {
 192         const struct cred *cred = current_cred();
 193         int i;
 194
 195         if (gidsetsize < 0)
 196                 return -EINVAL;
 197
 198         /* no need to grab task_lock here; it cannot change */
 199         i = cred->group_info->ngroups;
 200         if (gidsetsize) {
 201                 if (i > gidsetsize) {
 202                         i = -EINVAL;
 203                         goto out;
 204                 }
 205                 if (groups_to_user(grouplist, cred->group_info)) {
 206                         i = -EFAULT;
 207                         goto out;
 208                 }
 209         }
 210 out:
 211         return i;
 212 }
 213
 214 bool may_setgroups(void)
 215 {
 216         struct user_namespace *user_ns = current_user_ns();
 217
 218         return ns_capable(user_ns, CAP_SETGID) &&
 219                 userns_may_setgroups(user_ns);
 220 }
 221
 222 /*
 223  *      SMP: Our groups are copy-on-write. We can set them safely
 224  *      without another task interfering.
 225  */
 226
 227 SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
 228 {
 229         struct group_info *group_info;
 230         int retval;
 231
 232         if (!may_setgroups())
 233                 return -EPERM;
 234         if ((unsigned)gidsetsize > NGROUPS_MAX)
 235                 return -EINVAL;
 236
 237         group_info = groups_alloc(gidsetsize);
 238         if (!group_info)
 239                 return -ENOMEM;
 240         retval = groups_from_user(group_info, grouplist);
 241         if (retval) {
 242                 put_group_info(group_info);
 243                 return retval;
 244         }
 245
 246         retval = set_current_groups(group_info);
 247         put_group_info(group_info);
 248
 249         return retval;
 250 }
 251
 252 /*
 253  * Check whether we're fsgid/egid or in the supplemental group..
 254  */
 255 int in_group_p(kgid_t grp)
 256 {
 257         const struct cred *cred = current_cred();
 258         int retval = 1;
 259
 260         if (!gid_eq(grp, cred->fsgid))
 261                 retval = groups_search(cred->group_info, grp);
 262         return retval;
 263 }
 264
 265 EXPORT_SYMBOL(in_group_p);
 266
 267 int in_egroup_p(kgid_t grp)
 268 {
 269         const struct cred *cred = current_cred();
 270         int retval = 1;
 271
 272         if (!gid_eq(grp, cred->egid))
 273                 retval = groups_search(cred->group_info, grp);
 274         return retval;
 275 }
 276
 277 EXPORT_SYMBOL(in_egroup_p);