1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* scm.c - Socket level control messages processing.
3 *
4 * Author: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
5 * Alignment and value checking mods by Craig Metz
6 */
7
8 #include <linux/module.h>
9 #include <linux/signal.h>
10 #include <linux/capability.h>
11 #include <linux/errno.h>
12 #include <linux/sched.h>
13 #include <linux/sched/user.h>
14 #include <linux/mm.h>
15 #include <linux/kernel.h>
16 #include <linux/stat.h>
17 #include <linux/socket.h>
18 #include <linux/file.h>
19 #include <linux/fcntl.h>
20 #include <linux/net.h>
21 #include <linux/interrupt.h>
22 #include <linux/netdevice.h>
23 #include <linux/security.h>
24 #include <linux/pid_namespace.h>
25 #include <linux/pid.h>
26 #include <linux/nsproxy.h>
27 #include <linux/slab.h>
28 #include <linux/errqueue.h>
29
30 #include <linux/uaccess.h>
31
32 #include <net/protocol.h>
33 #include <linux/skbuff.h>
34 #include <net/sock.h>
35 #include <net/compat.h>
36 #include <net/scm.h>
37 #include <net/cls_cgroup.h>
38
39
40 /*
41 * Only allow a user to send credentials, that they could set with
42 * setu(g)id.
43 */
44
scm_check_creds(struct ucred * creds)45 static __inline__ int scm_check_creds(struct ucred *creds)
46 {
47 const struct cred *cred = current_cred();
48 kuid_t uid = make_kuid(cred->user_ns, creds->uid);
49 kgid_t gid = make_kgid(cred->user_ns, creds->gid);
50
51 if (!uid_valid(uid) || !gid_valid(gid))
52 return -EINVAL;
53
54 if ((creds->pid == task_tgid_vnr(current) ||
55 ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
56 ((uid_eq(uid, cred->uid) || uid_eq(uid, cred->euid) ||
57 uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
58 ((gid_eq(gid, cred->gid) || gid_eq(gid, cred->egid) ||
59 gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
60 return 0;
61 }
62 return -EPERM;
63 }
64
scm_fp_copy(struct cmsghdr * cmsg,struct scm_fp_list ** fplp)65 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
66 {
67 int *fdp = (int*)CMSG_DATA(cmsg);
68 struct scm_fp_list *fpl = *fplp;
69 struct file **fpp;
70 int i, num;
71
72 num = (cmsg->cmsg_len - sizeof(struct cmsghdr))/sizeof(int);
73
74 if (num <= 0)
75 return 0;
76
77 if (num > SCM_MAX_FD)
78 return -EINVAL;
79
80 if (!fpl)
81 {
82 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
83 if (!fpl)
84 return -ENOMEM;
85 *fplp = fpl;
86 fpl->count = 0;
87 fpl->max = SCM_MAX_FD;
88 fpl->user = NULL;
89 }
90 fpp = &fpl->fp[fpl->count];
91
92 if (fpl->count + num > fpl->max)
93 return -EINVAL;
94
95 /*
96 * Verify the descriptors and increment the usage count.
97 */
98
99 for (i=0; i< num; i++)
100 {
101 int fd = fdp[i];
102 struct file *file;
103
104 if (fd < 0 || !(file = fget_raw(fd)))
105 return -EBADF;
106 *fpp++ = file;
107 fpl->count++;
108 }
109
110 if (!fpl->user)
111 fpl->user = get_uid(current_user());
112
113 return num;
114 }
115
__scm_destroy(struct scm_cookie * scm)116 void __scm_destroy(struct scm_cookie *scm)
117 {
118 struct scm_fp_list *fpl = scm->fp;
119 int i;
120
121 if (fpl) {
122 scm->fp = NULL;
123 for (i=fpl->count-1; i>=0; i--)
124 fput(fpl->fp[i]);
125 free_uid(fpl->user);
126 kfree(fpl);
127 }
128 }
129 EXPORT_SYMBOL(__scm_destroy);
130
__scm_send(struct socket * sock,struct msghdr * msg,struct scm_cookie * p)131 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
132 {
133 struct cmsghdr *cmsg;
134 int err;
135
136 for_each_cmsghdr(cmsg, msg) {
137 err = -EINVAL;
138
139 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
140 /* The first check was omitted in <= 2.2.5. The reasoning was
141 that parser checks cmsg_len in any case, so that
142 additional check would be work duplication.
143 But if cmsg_level is not SOL_SOCKET, we do not check
144 for too short ancillary data object at all! Oops.
145 OK, let's add it...
146 */
147 if (!CMSG_OK(msg, cmsg))
148 goto error;
149
150 if (cmsg->cmsg_level != SOL_SOCKET)
151 continue;
152
153 switch (cmsg->cmsg_type)
154 {
155 case SCM_RIGHTS:
156 if (!sock->ops || sock->ops->family != PF_UNIX)
157 goto error;
158 err=scm_fp_copy(cmsg, &p->fp);
159 if (err<0)
160 goto error;
161 break;
162 case SCM_CREDENTIALS:
163 {
164 struct ucred creds;
165 kuid_t uid;
166 kgid_t gid;
167 if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
168 goto error;
169 memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
170 err = scm_check_creds(&creds);
171 if (err)
172 goto error;
173
174 p->creds.pid = creds.pid;
175 if (!p->pid || pid_vnr(p->pid) != creds.pid) {
176 struct pid *pid;
177 err = -ESRCH;
178 pid = find_get_pid(creds.pid);
179 if (!pid)
180 goto error;
181 put_pid(p->pid);
182 p->pid = pid;
183 }
184
185 err = -EINVAL;
186 uid = make_kuid(current_user_ns(), creds.uid);
187 gid = make_kgid(current_user_ns(), creds.gid);
188 if (!uid_valid(uid) || !gid_valid(gid))
189 goto error;
190
191 p->creds.uid = uid;
192 p->creds.gid = gid;
193 break;
194 }
195 default:
196 goto error;
197 }
198 }
199
200 if (p->fp && !p->fp->count)
201 {
202 kfree(p->fp);
203 p->fp = NULL;
204 }
205 return 0;
206
207 error:
208 scm_destroy(p);
209 return err;
210 }
211 EXPORT_SYMBOL(__scm_send);
212
put_cmsg(struct msghdr * msg,int level,int type,int len,void * data)213 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
214 {
215 int cmlen = CMSG_LEN(len);
216
217 if (msg->msg_flags & MSG_CMSG_COMPAT)
218 return put_cmsg_compat(msg, level, type, len, data);
219
220 if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
221 msg->msg_flags |= MSG_CTRUNC;
222 return 0; /* XXX: return error? check spec. */
223 }
224 if (msg->msg_controllen < cmlen) {
225 msg->msg_flags |= MSG_CTRUNC;
226 cmlen = msg->msg_controllen;
227 }
228
229 if (msg->msg_control_is_user) {
230 struct cmsghdr __user *cm = msg->msg_control_user;
231
232 if (!user_write_access_begin(cm, cmlen))
233 goto efault;
234
235 unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
236 unsafe_put_user(level, &cm->cmsg_level, efault_end);
237 unsafe_put_user(type, &cm->cmsg_type, efault_end);
238 unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
239 cmlen - sizeof(*cm), efault_end);
240 user_write_access_end();
241 } else {
242 struct cmsghdr *cm = msg->msg_control;
243
244 cm->cmsg_level = level;
245 cm->cmsg_type = type;
246 cm->cmsg_len = cmlen;
247 memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
248 }
249
250 cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
251 msg->msg_control += cmlen;
252 msg->msg_controllen -= cmlen;
253 return 0;
254
255 efault_end:
256 user_write_access_end();
257 efault:
258 return -EFAULT;
259 }
260 EXPORT_SYMBOL(put_cmsg);
261
put_cmsg_scm_timestamping64(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)262 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
263 {
264 struct scm_timestamping64 tss;
265 int i;
266
267 for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
268 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
269 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
270 }
271
272 put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
273 }
274 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
275
put_cmsg_scm_timestamping(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)276 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
277 {
278 struct scm_timestamping tss;
279 int i;
280
281 for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
282 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
283 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
284 }
285
286 put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
287 }
288 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
289
scm_max_fds(struct msghdr * msg)290 static int scm_max_fds(struct msghdr *msg)
291 {
292 if (msg->msg_controllen <= sizeof(struct cmsghdr))
293 return 0;
294 return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
295 }
296
scm_detach_fds(struct msghdr * msg,struct scm_cookie * scm)297 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
298 {
299 struct cmsghdr __user *cm =
300 (__force struct cmsghdr __user *)msg->msg_control;
301 unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
302 int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
303 int __user *cmsg_data = CMSG_USER_DATA(cm);
304 int err = 0, i;
305
306 /* no use for FD passing from kernel space callers */
307 if (WARN_ON_ONCE(!msg->msg_control_is_user))
308 return;
309
310 if (msg->msg_flags & MSG_CMSG_COMPAT) {
311 scm_detach_fds_compat(msg, scm);
312 return;
313 }
314
315 for (i = 0; i < fdmax; i++) {
316 err = receive_fd_user(scm->fp->fp[i], cmsg_data + i, o_flags);
317 if (err < 0)
318 break;
319 }
320
321 if (i > 0) {
322 int cmlen = CMSG_LEN(i * sizeof(int));
323
324 err = put_user(SOL_SOCKET, &cm->cmsg_level);
325 if (!err)
326 err = put_user(SCM_RIGHTS, &cm->cmsg_type);
327 if (!err)
328 err = put_user(cmlen, &cm->cmsg_len);
329 if (!err) {
330 cmlen = CMSG_SPACE(i * sizeof(int));
331 if (msg->msg_controllen < cmlen)
332 cmlen = msg->msg_controllen;
333 msg->msg_control += cmlen;
334 msg->msg_controllen -= cmlen;
335 }
336 }
337
338 if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
339 msg->msg_flags |= MSG_CTRUNC;
340
341 /*
342 * All of the files that fit in the message have had their usage counts
343 * incremented, so we just free the list.
344 */
345 __scm_destroy(scm);
346 }
347 EXPORT_SYMBOL(scm_detach_fds);
348
scm_fp_dup(struct scm_fp_list * fpl)349 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
350 {
351 struct scm_fp_list *new_fpl;
352 int i;
353
354 if (!fpl)
355 return NULL;
356
357 new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
358 GFP_KERNEL);
359 if (new_fpl) {
360 for (i = 0; i < fpl->count; i++)
361 get_file(fpl->fp[i]);
362 new_fpl->max = new_fpl->count;
363 new_fpl->user = get_uid(fpl->user);
364 }
365 return new_fpl;
366 }
367 EXPORT_SYMBOL(scm_fp_dup);
368