xref: /openbmc/linux/kernel/groups.c (revision 4da722ca)
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/sort.h>
9 #include <linux/syscalls.h>
10 #include <linux/user_namespace.h>
11 #include <linux/vmalloc.h>
12 #include <linux/uaccess.h>
13 
14 struct group_info *groups_alloc(int gidsetsize)
15 {
16 	struct group_info *gi;
17 	unsigned int len;
18 
19 	len = sizeof(struct group_info) + sizeof(kgid_t) * gidsetsize;
20 	gi = kmalloc(len, GFP_KERNEL_ACCOUNT|__GFP_NOWARN|__GFP_NORETRY);
21 	if (!gi)
22 		gi = __vmalloc(len, GFP_KERNEL_ACCOUNT, PAGE_KERNEL);
23 	if (!gi)
24 		return NULL;
25 
26 	atomic_set(&gi->usage, 1);
27 	gi->ngroups = gidsetsize;
28 	return gi;
29 }
30 
31 EXPORT_SYMBOL(groups_alloc);
32 
33 void groups_free(struct group_info *group_info)
34 {
35 	kvfree(group_info);
36 }
37 
38 EXPORT_SYMBOL(groups_free);
39 
40 /* export the group_info to a user-space array */
41 static int groups_to_user(gid_t __user *grouplist,
42 			  const struct group_info *group_info)
43 {
44 	struct user_namespace *user_ns = current_user_ns();
45 	int i;
46 	unsigned int count = group_info->ngroups;
47 
48 	for (i = 0; i < count; i++) {
49 		gid_t gid;
50 		gid = from_kgid_munged(user_ns, group_info->gid[i]);
51 		if (put_user(gid, grouplist+i))
52 			return -EFAULT;
53 	}
54 	return 0;
55 }
56 
57 /* fill a group_info from a user-space array - it must be allocated already */
58 static int groups_from_user(struct group_info *group_info,
59     gid_t __user *grouplist)
60 {
61 	struct user_namespace *user_ns = current_user_ns();
62 	int i;
63 	unsigned int count = group_info->ngroups;
64 
65 	for (i = 0; i < count; i++) {
66 		gid_t gid;
67 		kgid_t kgid;
68 		if (get_user(gid, grouplist+i))
69 			return -EFAULT;
70 
71 		kgid = make_kgid(user_ns, gid);
72 		if (!gid_valid(kgid))
73 			return -EINVAL;
74 
75 		group_info->gid[i] = kgid;
76 	}
77 	return 0;
78 }
79 
80 static int gid_cmp(const void *_a, const void *_b)
81 {
82 	kgid_t a = *(kgid_t *)_a;
83 	kgid_t b = *(kgid_t *)_b;
84 
85 	return gid_gt(a, b) - gid_lt(a, b);
86 }
87 
88 static void groups_sort(struct group_info *group_info)
89 {
90 	sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
91 	     gid_cmp, NULL);
92 }
93 
94 /* a simple bsearch */
95 int groups_search(const struct group_info *group_info, kgid_t grp)
96 {
97 	unsigned int left, right;
98 
99 	if (!group_info)
100 		return 0;
101 
102 	left = 0;
103 	right = group_info->ngroups;
104 	while (left < right) {
105 		unsigned int mid = (left+right)/2;
106 		if (gid_gt(grp, group_info->gid[mid]))
107 			left = mid + 1;
108 		else if (gid_lt(grp, group_info->gid[mid]))
109 			right = mid;
110 		else
111 			return 1;
112 	}
113 	return 0;
114 }
115 
116 /**
117  * set_groups - Change a group subscription in a set of credentials
118  * @new: The newly prepared set of credentials to alter
119  * @group_info: The group list to install
120  */
121 void set_groups(struct cred *new, struct group_info *group_info)
122 {
123 	put_group_info(new->group_info);
124 	groups_sort(group_info);
125 	get_group_info(group_info);
126 	new->group_info = group_info;
127 }
128 
129 EXPORT_SYMBOL(set_groups);
130 
131 /**
132  * set_current_groups - Change current's group subscription
133  * @group_info: The group list to impose
134  *
135  * Validate a group subscription and, if valid, impose it upon current's task
136  * security record.
137  */
138 int set_current_groups(struct group_info *group_info)
139 {
140 	struct cred *new;
141 
142 	new = prepare_creds();
143 	if (!new)
144 		return -ENOMEM;
145 
146 	set_groups(new, group_info);
147 	return commit_creds(new);
148 }
149 
150 EXPORT_SYMBOL(set_current_groups);
151 
152 SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
153 {
154 	const struct cred *cred = current_cred();
155 	int i;
156 
157 	if (gidsetsize < 0)
158 		return -EINVAL;
159 
160 	/* no need to grab task_lock here; it cannot change */
161 	i = cred->group_info->ngroups;
162 	if (gidsetsize) {
163 		if (i > gidsetsize) {
164 			i = -EINVAL;
165 			goto out;
166 		}
167 		if (groups_to_user(grouplist, cred->group_info)) {
168 			i = -EFAULT;
169 			goto out;
170 		}
171 	}
172 out:
173 	return i;
174 }
175 
176 bool may_setgroups(void)
177 {
178 	struct user_namespace *user_ns = current_user_ns();
179 
180 	return ns_capable(user_ns, CAP_SETGID) &&
181 		userns_may_setgroups(user_ns);
182 }
183 
184 /*
185  *	SMP: Our groups are copy-on-write. We can set them safely
186  *	without another task interfering.
187  */
188 
189 SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
190 {
191 	struct group_info *group_info;
192 	int retval;
193 
194 	if (!may_setgroups())
195 		return -EPERM;
196 	if ((unsigned)gidsetsize > NGROUPS_MAX)
197 		return -EINVAL;
198 
199 	group_info = groups_alloc(gidsetsize);
200 	if (!group_info)
201 		return -ENOMEM;
202 	retval = groups_from_user(group_info, grouplist);
203 	if (retval) {
204 		put_group_info(group_info);
205 		return retval;
206 	}
207 
208 	retval = set_current_groups(group_info);
209 	put_group_info(group_info);
210 
211 	return retval;
212 }
213 
214 /*
215  * Check whether we're fsgid/egid or in the supplemental group..
216  */
217 int in_group_p(kgid_t grp)
218 {
219 	const struct cred *cred = current_cred();
220 	int retval = 1;
221 
222 	if (!gid_eq(grp, cred->fsgid))
223 		retval = groups_search(cred->group_info, grp);
224 	return retval;
225 }
226 
227 EXPORT_SYMBOL(in_group_p);
228 
229 int in_egroup_p(kgid_t grp)
230 {
231 	const struct cred *cred = current_cred();
232 	int retval = 1;
233 
234 	if (!gid_eq(grp, cred->egid))
235 		retval = groups_search(cred->group_info, grp);
236 	return retval;
237 }
238 
239 EXPORT_SYMBOL(in_egroup_p);
240