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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 <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);
278 

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