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 <uapi/linux/pidfd.h>
27 #include <linux/pidfs.h>
28 #include <linux/nsproxy.h>
29 #include <linux/slab.h>
30 #include <linux/errqueue.h>
31 #include <linux/io_uring.h>
32
33 #include <linux/uaccess.h>
34
35 #include <net/protocol.h>
36 #include <linux/skbuff.h>
37 #include <net/sock.h>
38 #include <net/compat.h>
39 #include <net/scm.h>
40 #include <net/cls_cgroup.h>
41 #include <net/af_unix.h>
42
43
44 /*
45 * Only allow a user to send credentials, that they could set with
46 * setu(g)id.
47 */
48
scm_check_creds(struct ucred * creds)49 static __inline__ int scm_check_creds(struct ucred *creds)
50 {
51 const struct cred *cred = current_cred();
52 kuid_t uid = make_kuid(cred->user_ns, creds->uid);
53 kgid_t gid = make_kgid(cred->user_ns, creds->gid);
54
55 if (!uid_valid(uid) || !gid_valid(gid))
56 return -EINVAL;
57
58 if ((creds->pid == task_tgid_vnr(current) ||
59 ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
60 ((uid_eq(uid, cred->uid) || uid_eq(uid, cred->euid) ||
61 uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
62 ((gid_eq(gid, cred->gid) || gid_eq(gid, cred->egid) ||
63 gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
64 return 0;
65 }
66 return -EPERM;
67 }
68
scm_fp_copy(struct cmsghdr * cmsg,struct scm_fp_list ** fplp)69 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
70 {
71 int *fdp = (int*)CMSG_DATA(cmsg);
72 struct scm_fp_list *fpl = *fplp;
73 struct file **fpp;
74 int i, num;
75
76 num = (cmsg->cmsg_len - sizeof(struct cmsghdr))/sizeof(int);
77
78 if (num <= 0)
79 return 0;
80
81 if (num > SCM_MAX_FD)
82 return -EINVAL;
83
84 if (!fpl)
85 {
86 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL_ACCOUNT);
87 if (!fpl)
88 return -ENOMEM;
89 *fplp = fpl;
90 fpl->count = 0;
91 fpl->count_unix = 0;
92 fpl->max = SCM_MAX_FD;
93 fpl->user = NULL;
94 #if IS_ENABLED(CONFIG_UNIX)
95 fpl->inflight = false;
96 fpl->dead = false;
97 fpl->edges = NULL;
98 INIT_LIST_HEAD(&fpl->vertices);
99 #endif
100 }
101 fpp = &fpl->fp[fpl->count];
102
103 if (fpl->count + num > fpl->max)
104 return -EINVAL;
105
106 /*
107 * Verify the descriptors and increment the usage count.
108 */
109
110 for (i=0; i< num; i++)
111 {
112 int fd = fdp[i];
113 struct file *file;
114
115 if (fd < 0 || !(file = fget_raw(fd)))
116 return -EBADF;
117 /* don't allow io_uring files */
118 if (io_is_uring_fops(file)) {
119 fput(file);
120 return -EINVAL;
121 }
122 if (unix_get_socket(file))
123 fpl->count_unix++;
124
125 *fpp++ = file;
126 fpl->count++;
127 }
128
129 if (!fpl->user)
130 fpl->user = get_uid(current_user());
131
132 return num;
133 }
134
__scm_destroy(struct scm_cookie * scm)135 void __scm_destroy(struct scm_cookie *scm)
136 {
137 struct scm_fp_list *fpl = scm->fp;
138 int i;
139
140 if (fpl) {
141 scm->fp = NULL;
142 for (i=fpl->count-1; i>=0; i--)
143 fput(fpl->fp[i]);
144 free_uid(fpl->user);
145 kfree(fpl);
146 }
147 }
148 EXPORT_SYMBOL(__scm_destroy);
149
scm_replace_pid(struct scm_cookie * scm,struct pid * pid)150 static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
151 {
152 int err;
153
154 /* drop all previous references */
155 scm_destroy_cred(scm);
156
157 err = pidfs_register_pid(pid);
158 if (unlikely(err))
159 return err;
160
161 scm->pid = pid;
162 scm->creds.pid = pid_vnr(pid);
163 return 0;
164 }
165
__scm_send(struct socket * sock,struct msghdr * msg,struct scm_cookie * p)166 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
167 {
168 const struct proto_ops *ops = READ_ONCE(sock->ops);
169 struct cmsghdr *cmsg;
170 int err;
171
172 for_each_cmsghdr(cmsg, msg) {
173 err = -EINVAL;
174
175 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
176 /* The first check was omitted in <= 2.2.5. The reasoning was
177 that parser checks cmsg_len in any case, so that
178 additional check would be work duplication.
179 But if cmsg_level is not SOL_SOCKET, we do not check
180 for too short ancillary data object at all! Oops.
181 OK, let's add it...
182 */
183 if (!CMSG_OK(msg, cmsg))
184 goto error;
185
186 if (cmsg->cmsg_level != SOL_SOCKET)
187 continue;
188
189 switch (cmsg->cmsg_type)
190 {
191 case SCM_RIGHTS:
192 if (!ops || ops->family != PF_UNIX)
193 goto error;
194 err=scm_fp_copy(cmsg, &p->fp);
195 if (err<0)
196 goto error;
197 break;
198 case SCM_CREDENTIALS:
199 {
200 struct ucred creds;
201 kuid_t uid;
202 kgid_t gid;
203 if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
204 goto error;
205 memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
206 err = scm_check_creds(&creds);
207 if (err)
208 goto error;
209
210 if (!p->pid || pid_vnr(p->pid) != creds.pid) {
211 struct pid *pid;
212 err = -ESRCH;
213 pid = find_get_pid(creds.pid);
214 if (!pid)
215 goto error;
216
217 /* pass a struct pid reference from
218 * find_get_pid() to scm_replace_pid().
219 */
220 err = scm_replace_pid(p, pid);
221 if (err) {
222 put_pid(pid);
223 goto error;
224 }
225 }
226
227 err = -EINVAL;
228 uid = make_kuid(current_user_ns(), creds.uid);
229 gid = make_kgid(current_user_ns(), creds.gid);
230 if (!uid_valid(uid) || !gid_valid(gid))
231 goto error;
232
233 p->creds.uid = uid;
234 p->creds.gid = gid;
235 break;
236 }
237 default:
238 goto error;
239 }
240 }
241
242 if (p->fp && !p->fp->count)
243 {
244 kfree(p->fp);
245 p->fp = NULL;
246 }
247 return 0;
248
249 error:
250 scm_destroy(p);
251 return err;
252 }
253 EXPORT_SYMBOL(__scm_send);
254
put_cmsg(struct msghdr * msg,int level,int type,int len,void * data)255 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
256 {
257 int cmlen = CMSG_LEN(len);
258
259 if (msg->msg_flags & MSG_CMSG_COMPAT)
260 return put_cmsg_compat(msg, level, type, len, data);
261
262 if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
263 msg->msg_flags |= MSG_CTRUNC;
264 return 0; /* XXX: return error? check spec. */
265 }
266 if (msg->msg_controllen < cmlen) {
267 msg->msg_flags |= MSG_CTRUNC;
268 cmlen = msg->msg_controllen;
269 }
270
271 if (msg->msg_control_is_user) {
272 struct cmsghdr __user *cm = msg->msg_control_user;
273
274 check_object_size(data, cmlen - sizeof(*cm), true);
275
276 if (!user_write_access_begin(cm, cmlen))
277 goto efault;
278
279 unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
280 unsafe_put_user(level, &cm->cmsg_level, efault_end);
281 unsafe_put_user(type, &cm->cmsg_type, efault_end);
282 unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
283 cmlen - sizeof(*cm), efault_end);
284 user_write_access_end();
285 } else {
286 struct cmsghdr *cm = msg->msg_control;
287
288 cm->cmsg_level = level;
289 cm->cmsg_type = type;
290 cm->cmsg_len = cmlen;
291 memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
292 }
293
294 cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
295 if (msg->msg_control_is_user)
296 msg->msg_control_user += cmlen;
297 else
298 msg->msg_control += cmlen;
299 msg->msg_controllen -= cmlen;
300 return 0;
301
302 efault_end:
303 user_write_access_end();
304 efault:
305 return -EFAULT;
306 }
307 EXPORT_SYMBOL(put_cmsg);
308
put_cmsg_notrunc(struct msghdr * msg,int level,int type,int len,void * data)309 int put_cmsg_notrunc(struct msghdr *msg, int level, int type, int len,
310 void *data)
311 {
312 /* Don't produce truncated CMSGs */
313 if (!msg->msg_control || msg->msg_controllen < CMSG_LEN(len))
314 return -ETOOSMALL;
315
316 return put_cmsg(msg, level, type, len, data);
317 }
318
put_cmsg_scm_timestamping64(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)319 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
320 {
321 struct scm_timestamping64 tss;
322 int i;
323
324 for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
325 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
326 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
327 }
328
329 put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
330 }
331 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
332
put_cmsg_scm_timestamping(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)333 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
334 {
335 struct scm_timestamping tss;
336 int i;
337
338 for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
339 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
340 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
341 }
342
343 put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
344 }
345 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
346
scm_max_fds(struct msghdr * msg)347 static int scm_max_fds(struct msghdr *msg)
348 {
349 if (msg->msg_controllen <= sizeof(struct cmsghdr))
350 return 0;
351 return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
352 }
353
scm_detach_fds(struct msghdr * msg,struct scm_cookie * scm)354 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
355 {
356 struct cmsghdr __user *cm =
357 (__force struct cmsghdr __user *)msg->msg_control_user;
358 unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
359 int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
360 int __user *cmsg_data = CMSG_USER_DATA(cm);
361 int err = 0, i;
362
363 /* no use for FD passing from kernel space callers */
364 if (WARN_ON_ONCE(!msg->msg_control_is_user))
365 return;
366
367 if (msg->msg_flags & MSG_CMSG_COMPAT) {
368 scm_detach_fds_compat(msg, scm);
369 return;
370 }
371
372 for (i = 0; i < fdmax; i++) {
373 err = scm_recv_one_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
374 if (err < 0)
375 break;
376 }
377
378 if (i > 0) {
379 int cmlen = CMSG_LEN(i * sizeof(int));
380
381 err = put_user(SOL_SOCKET, &cm->cmsg_level);
382 if (!err)
383 err = put_user(SCM_RIGHTS, &cm->cmsg_type);
384 if (!err)
385 err = put_user(cmlen, &cm->cmsg_len);
386 if (!err) {
387 cmlen = CMSG_SPACE(i * sizeof(int));
388 if (msg->msg_controllen < cmlen)
389 cmlen = msg->msg_controllen;
390 msg->msg_control_user += cmlen;
391 msg->msg_controllen -= cmlen;
392 }
393 }
394
395 if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
396 msg->msg_flags |= MSG_CTRUNC;
397
398 /*
399 * All of the files that fit in the message have had their usage counts
400 * incremented, so we just free the list.
401 */
402 __scm_destroy(scm);
403 }
404 EXPORT_SYMBOL(scm_detach_fds);
405
scm_fp_dup(struct scm_fp_list * fpl)406 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
407 {
408 struct scm_fp_list *new_fpl;
409 int i;
410
411 if (!fpl)
412 return NULL;
413
414 new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
415 GFP_KERNEL_ACCOUNT);
416 if (new_fpl) {
417 for (i = 0; i < fpl->count; i++)
418 get_file(fpl->fp[i]);
419
420 new_fpl->max = new_fpl->count;
421 new_fpl->user = get_uid(fpl->user);
422 #if IS_ENABLED(CONFIG_UNIX)
423 new_fpl->inflight = false;
424 new_fpl->edges = NULL;
425 INIT_LIST_HEAD(&new_fpl->vertices);
426 #endif
427 }
428 return new_fpl;
429 }
430 EXPORT_SYMBOL(scm_fp_dup);
431
432 #ifdef CONFIG_SECURITY_NETWORK
scm_passec(struct sock * sk,struct msghdr * msg,struct scm_cookie * scm)433 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
434 {
435 struct lsm_context ctx;
436 int err;
437
438 if (sk->sk_scm_security) {
439 err = security_secid_to_secctx(scm->secid, &ctx);
440
441 if (err >= 0) {
442 put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, ctx.len,
443 ctx.context);
444
445 security_release_secctx(&ctx);
446 }
447 }
448 }
449
scm_has_secdata(struct sock * sk)450 static bool scm_has_secdata(struct sock *sk)
451 {
452 return sk->sk_scm_security;
453 }
454 #else
scm_passec(struct sock * sk,struct msghdr * msg,struct scm_cookie * scm)455 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
456 {
457 }
458
scm_has_secdata(struct sock * sk)459 static bool scm_has_secdata(struct sock *sk)
460 {
461 return false;
462 }
463 #endif
464
scm_pidfd_recv(struct msghdr * msg,struct scm_cookie * scm)465 static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
466 {
467 struct file *pidfd_file = NULL;
468 int len, pidfd;
469
470 /* put_cmsg() doesn't return an error if CMSG is truncated,
471 * that's why we need to opencode these checks here.
472 */
473 if (msg->msg_flags & MSG_CMSG_COMPAT)
474 len = sizeof(struct compat_cmsghdr) + sizeof(int);
475 else
476 len = sizeof(struct cmsghdr) + sizeof(int);
477
478 if (msg->msg_controllen < len) {
479 msg->msg_flags |= MSG_CTRUNC;
480 return;
481 }
482
483 if (!scm->pid)
484 return;
485
486 pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
487
488 if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
489 if (pidfd_file) {
490 put_unused_fd(pidfd);
491 fput(pidfd_file);
492 }
493
494 return;
495 }
496
497 if (pidfd_file)
498 fd_install(pidfd, pidfd_file);
499 }
500
__scm_recv_common(struct sock * sk,struct msghdr * msg,struct scm_cookie * scm,int flags)501 static bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
502 struct scm_cookie *scm, int flags)
503 {
504 if (!msg->msg_control) {
505 if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
506 scm->fp || scm_has_secdata(sk))
507 msg->msg_flags |= MSG_CTRUNC;
508
509 scm_destroy(scm);
510 return false;
511 }
512
513 if (sk->sk_scm_credentials) {
514 struct user_namespace *current_ns = current_user_ns();
515 struct ucred ucreds = {
516 .pid = scm->creds.pid,
517 .uid = from_kuid_munged(current_ns, scm->creds.uid),
518 .gid = from_kgid_munged(current_ns, scm->creds.gid),
519 };
520
521 put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
522 }
523
524 scm_passec(sk, msg, scm);
525
526 if (scm->fp)
527 scm_detach_fds(msg, scm);
528
529 return true;
530 }
531
scm_recv(struct socket * sock,struct msghdr * msg,struct scm_cookie * scm,int flags)532 void scm_recv(struct socket *sock, struct msghdr *msg,
533 struct scm_cookie *scm, int flags)
534 {
535 if (!__scm_recv_common(sock->sk, msg, scm, flags))
536 return;
537
538 scm_destroy_cred(scm);
539 }
540 EXPORT_SYMBOL(scm_recv);
541
scm_recv_unix(struct socket * sock,struct msghdr * msg,struct scm_cookie * scm,int flags)542 void scm_recv_unix(struct socket *sock, struct msghdr *msg,
543 struct scm_cookie *scm, int flags)
544 {
545 if (!__scm_recv_common(sock->sk, msg, scm, flags))
546 return;
547
548 if (sock->sk->sk_scm_pidfd)
549 scm_pidfd_recv(msg, scm);
550
551 scm_destroy_cred(scm);
552 }
553