kernel/groups.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Supplementary group IDs
   4  */
   5 #include <linux/cred.h>
   6 #include <linux/export.h>
   7 #include <linux/slab.h>
   8 #include <linux/security.h>
   9 #include <linux/sort.h>
  10 #include <linux/syscalls.h>
  11 #include <linux/user_namespace.h>
  12 #include <linux/vmalloc.h>
  13 #include <linux/uaccess.h>
  14
  15 struct group_info *groups_alloc(int gidsetsize)
  16 {
  17         struct group_info *gi;
  18         gi = kvmalloc(struct_size(gi, gid, gidsetsize), GFP_KERNEL_ACCOUNT);
  19         if (!gi)
  20                 return NULL;
  21
  22         refcount_set(&gi->usage, 1);
  23         gi->ngroups = gidsetsize;
  24         return gi;
  25 }
  26
  27 EXPORT_SYMBOL(groups_alloc);
  28
  29 void groups_free(struct group_info *group_info)
  30 {
  31         kvfree(group_info);
  32 }
  33
  34 EXPORT_SYMBOL(groups_free);
  35
  36 /* export the group_info to a user-space array */
  37 static int groups_to_user(gid_t __user *grouplist,
  38                           const struct group_info *group_info)
  39 {
  40         struct user_namespace *user_ns = current_user_ns();
  41         int i;
  42         unsigned int count = group_info->ngroups;
  43
  44         for (i = 0; i < count; i++) {
  45                 gid_t gid;
  46                 gid = from_kgid_munged(user_ns, group_info->gid[i]);
  47                 if (put_user(gid, grouplist+i))
  48                         return -EFAULT;
  49         }
  50         return 0;
  51 }
  52
  53 /* fill a group_info from a user-space array - it must be allocated already */
  54 static int groups_from_user(struct group_info *group_info,
  55     gid_t __user *grouplist)
  56 {
  57         struct user_namespace *user_ns = current_user_ns();
  58         int i;
  59         unsigned int count = group_info->ngroups;
  60
  61         for (i = 0; i < count; i++) {
  62                 gid_t gid;
  63                 kgid_t kgid;
  64                 if (get_user(gid, grouplist+i))
  65                         return -EFAULT;
  66
  67                 kgid = make_kgid(user_ns, gid);
  68                 if (!gid_valid(kgid))
  69                         return -EINVAL;
  70
  71                 group_info->gid[i] = kgid;
  72         }
  73         return 0;
  74 }
  75
  76 static int gid_cmp(const void *_a, const void *_b)
  77 {
  78         kgid_t a = *(kgid_t *)_a;
  79         kgid_t b = *(kgid_t *)_b;
  80
  81         return gid_gt(a, b) - gid_lt(a, b);
  82 }
  83
  84 void groups_sort(struct group_info *group_info)
  85 {
  86         sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
  87              gid_cmp, NULL);
  88 }
  89 EXPORT_SYMBOL(groups_sort);
  90
  91 /* a simple bsearch */
  92 int groups_search(const struct group_info *group_info, kgid_t grp)
  93 {
  94         unsigned int left, right;
  95
  96         if (!group_info)
  97                 return 0;
  98
  99         left = 0;
 100         right = group_info->ngroups;
 101         while (left < right) {
 102                 unsigned int mid = (left+right)/2;
 103                 if (gid_gt(grp, group_info->gid[mid]))
 104                         left = mid + 1;
 105                 else if (gid_lt(grp, group_info->gid[mid]))
 106                         right = mid;
 107                 else
 108                         return 1;
 109         }
 110         return 0;
 111 }
 112
 113 /**
 114  * set_groups - Change a group subscription in a set of credentials
 115  * @new: The newly prepared set of credentials to alter
 116  * @group_info: The group list to install
 117  */
 118 void set_groups(struct cred *new, struct group_info *group_info)
 119 {
 120         put_group_info(new->group_info);
 121         get_group_info(group_info);
 122         new->group_info = group_info;
 123 }
 124
 125 EXPORT_SYMBOL(set_groups);
 126
 127 /**
 128  * set_current_groups - Change current's group subscription
 129  * @group_info: The group list to impose
 130  *
 131  * Validate a group subscription and, if valid, impose it upon current's task
 132  * security record.
 133  */
 134 int set_current_groups(struct group_info *group_info)
 135 {
 136         struct cred *new;
 137         const struct cred *old;
 138         int retval;
 139
 140         new = prepare_creds();
 141         if (!new)
 142                 return -ENOMEM;
 143
 144         old = current_cred();
 145
 146         set_groups(new, group_info);
 147
 148         retval = security_task_fix_setgroups(new, old);
 149         if (retval < 0)
 150                 goto error;
 151
 152         return commit_creds(new);
 153
 154 error:
 155         abort_creds(new);
 156         return retval;
 157 }
 158
 159 EXPORT_SYMBOL(set_current_groups);
 160
 161 SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
 162 {
 163         const struct cred *cred = current_cred();
 164         int i;
 165
 166         if (gidsetsize < 0)
 167                 return -EINVAL;
 168
 169         /* no need to grab task_lock here; it cannot change */
 170         i = cred->group_info->ngroups;
 171         if (gidsetsize) {
 172                 if (i > gidsetsize) {
 173                         i = -EINVAL;
 174                         goto out;
 175                 }
 176                 if (groups_to_user(grouplist, cred->group_info)) {
 177                         i = -EFAULT;
 178                         goto out;
 179                 }
 180         }
 181 out:
 182         return i;
 183 }
 184
 185 bool may_setgroups(void)
 186 {
 187         struct user_namespace *user_ns = current_user_ns();
 188
 189         return ns_capable_setid(user_ns, CAP_SETGID) &&
 190                 userns_may_setgroups(user_ns);
 191 }
 192
 193 /*
 194  *      SMP: Our groups are copy-on-write. We can set them safely
 195  *      without another task interfering.
 196  */
 197
 198 SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
 199 {
 200         struct group_info *group_info;
 201         int retval;
 202
 203         if (!may_setgroups())
 204                 return -EPERM;
 205         if ((unsigned)gidsetsize > NGROUPS_MAX)
 206                 return -EINVAL;
 207
 208         group_info = groups_alloc(gidsetsize);
 209         if (!group_info)
 210                 return -ENOMEM;
 211         retval = groups_from_user(group_info, grouplist);
 212         if (retval) {
 213                 put_group_info(group_info);
 214                 return retval;
 215         }
 216
 217         groups_sort(group_info);
 218         retval = set_current_groups(group_info);
 219         put_group_info(group_info);
 220
 221         return retval;
 222 }
 223
 224 /*
 225  * Check whether we're fsgid/egid or in the supplemental group..
 226  */
 227 int in_group_p(kgid_t grp)
 228 {
 229         const struct cred *cred = current_cred();
 230         int retval = 1;
 231
 232         if (!gid_eq(grp, cred->fsgid))
 233                 retval = groups_search(cred->group_info, grp);
 234         return retval;
 235 }
 236
 237 EXPORT_SYMBOL(in_group_p);
 238
 239 int in_egroup_p(kgid_t grp)
 240 {
 241         const struct cred *cred = current_cred();
 242         int retval = 1;
 243
 244         if (!gid_eq(grp, cred->egid))
 245                 retval = groups_search(cred->group_info, grp);
 246         return retval;
 247 }
 248
 249 EXPORT_SYMBOL(in_egroup_p);