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
groups_alloc(int gidsetsize)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
groups_free(struct group_info * group_info)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 */
groups_to_user(gid_t __user * grouplist,const struct group_info * group_info)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 */
groups_from_user(struct group_info * group_info,gid_t __user * grouplist)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
gid_cmp(const void * _a,const void * _b)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
groups_sort(struct group_info * group_info)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 */
groups_search(const struct group_info * group_info,kgid_t grp)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 */
set_groups(struct cred * new,struct group_info * group_info)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 */
set_current_groups(struct group_info * group_info)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
SYSCALL_DEFINE2(getgroups,int,gidsetsize,gid_t __user *,grouplist)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
may_setgroups(void)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
SYSCALL_DEFINE2(setgroups,int,gidsetsize,gid_t __user *,grouplist)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 */
in_group_p(kgid_t grp)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
in_egroup_p(kgid_t grp)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);
250