linux/kernel/groups.c
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   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 */
  12struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
  13
  14struct 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
  43out_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
  51EXPORT_SYMBOL(groups_alloc);
  52
  53void 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
  63EXPORT_SYMBOL(groups_free);
  64
  65/* export the group_info to a user-space array */
  66static 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 */
  83static 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 */
 106static 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 */
 135int 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 * Validate a group subscription and, if valid, insert it into a set
 162 * of credentials.
 163 */
 164int set_groups(struct cred *new, struct group_info *group_info)
 165{
 166        put_group_info(new->group_info);
 167        groups_sort(group_info);
 168        get_group_info(group_info);
 169        new->group_info = group_info;
 170        return 0;
 171}
 172
 173EXPORT_SYMBOL(set_groups);
 174
 175/**
 176 * set_current_groups - Change current's group subscription
 177 * @group_info: The group list to impose
 178 *
 179 * Validate a group subscription and, if valid, impose it upon current's task
 180 * security record.
 181 */
 182int set_current_groups(struct group_info *group_info)
 183{
 184        struct cred *new;
 185        int ret;
 186
 187        new = prepare_creds();
 188        if (!new)
 189                return -ENOMEM;
 190
 191        ret = set_groups(new, group_info);
 192        if (ret < 0) {
 193                abort_creds(new);
 194                return ret;
 195        }
 196
 197        return commit_creds(new);
 198}
 199
 200EXPORT_SYMBOL(set_current_groups);
 201
 202SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
 203{
 204        const struct cred *cred = current_cred();
 205        int i;
 206
 207        if (gidsetsize < 0)
 208                return -EINVAL;
 209
 210        /* no need to grab task_lock here; it cannot change */
 211        i = cred->group_info->ngroups;
 212        if (gidsetsize) {
 213                if (i > gidsetsize) {
 214                        i = -EINVAL;
 215                        goto out;
 216                }
 217                if (groups_to_user(grouplist, cred->group_info)) {
 218                        i = -EFAULT;
 219                        goto out;
 220                }
 221        }
 222out:
 223        return i;
 224}
 225
 226/*
 227 *      SMP: Our groups are copy-on-write. We can set them safely
 228 *      without another task interfering.
 229 */
 230
 231SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
 232{
 233        struct group_info *group_info;
 234        int retval;
 235
 236        if (!nsown_capable(CAP_SETGID))
 237                return -EPERM;
 238        if ((unsigned)gidsetsize > NGROUPS_MAX)
 239                return -EINVAL;
 240
 241        group_info = groups_alloc(gidsetsize);
 242        if (!group_info)
 243                return -ENOMEM;
 244        retval = groups_from_user(group_info, grouplist);
 245        if (retval) {
 246                put_group_info(group_info);
 247                return retval;
 248        }
 249
 250        retval = set_current_groups(group_info);
 251        put_group_info(group_info);
 252
 253        return retval;
 254}
 255
 256/*
 257 * Check whether we're fsgid/egid or in the supplemental group..
 258 */
 259int in_group_p(kgid_t grp)
 260{
 261        const struct cred *cred = current_cred();
 262        int retval = 1;
 263
 264        if (!gid_eq(grp, cred->fsgid))
 265                retval = groups_search(cred->group_info, grp);
 266        return retval;
 267}
 268
 269EXPORT_SYMBOL(in_group_p);
 270
 271int in_egroup_p(kgid_t grp)
 272{
 273        const struct cred *cred = current_cred();
 274        int retval = 1;
 275
 276        if (!gid_eq(grp, cred->egid))
 277                retval = groups_search(cred->group_info, grp);
 278        return retval;
 279}
 280
 281EXPORT_SYMBOL(in_egroup_p);
 282
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