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Linux/kernel/groups.c

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

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