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Linux/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);
272 

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