xref: /linux/net/core/scm.c (revision 7fc2cd2e4b398c57c9cf961cfea05eadbf34c05c) 
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 
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 
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 
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 
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 
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 
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 		scoped_user_write_access_size(cm, cmlen, efault) {
277 			unsafe_put_user(cmlen, &cm->cmsg_len, efault);
278 			unsafe_put_user(level, &cm->cmsg_level, efault);
279 			unsafe_put_user(type, &cm->cmsg_type, efault);
280 			unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
281 					    cmlen - sizeof(*cm), efault);
282 		}
283 	} else {
284 		struct cmsghdr *cm = msg->msg_control;
285 
286 		cm->cmsg_level = level;
287 		cm->cmsg_type = type;
288 		cm->cmsg_len = cmlen;
289 		memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
290 	}
291 
292 	cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
293 	if (msg->msg_control_is_user)
294 		msg->msg_control_user += cmlen;
295 	else
296 		msg->msg_control += cmlen;
297 	msg->msg_controllen -= cmlen;
298 	return 0;
299 
300 efault:
301 	return -EFAULT;
302 }
303 EXPORT_SYMBOL(put_cmsg);
304 
305 int put_cmsg_notrunc(struct msghdr *msg, int level, int type, int len,
306 		     void *data)
307 {
308 	/* Don't produce truncated CMSGs */
309 	if (!msg->msg_control || msg->msg_controllen < CMSG_LEN(len))
310 		return -ETOOSMALL;
311 
312 	return put_cmsg(msg, level, type, len, data);
313 }
314 
315 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
316 {
317 	struct scm_timestamping64 tss;
318 	int i;
319 
320 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
321 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
322 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
323 	}
324 
325 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
326 }
327 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
328 
329 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
330 {
331 	struct scm_timestamping tss;
332 	int i;
333 
334 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
335 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
336 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
337 	}
338 
339 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
340 }
341 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
342 
343 static int scm_max_fds(struct msghdr *msg)
344 {
345 	if (msg->msg_controllen <= sizeof(struct cmsghdr))
346 		return 0;
347 	return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
348 }
349 
350 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
351 {
352 	struct cmsghdr __user *cm =
353 		(__force struct cmsghdr __user *)msg->msg_control_user;
354 	unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
355 	int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
356 	int __user *cmsg_data = CMSG_USER_DATA(cm);
357 	int err = 0, i;
358 
359 	/* no use for FD passing from kernel space callers */
360 	if (WARN_ON_ONCE(!msg->msg_control_is_user))
361 		return;
362 
363 	if (msg->msg_flags & MSG_CMSG_COMPAT) {
364 		scm_detach_fds_compat(msg, scm);
365 		return;
366 	}
367 
368 	for (i = 0; i < fdmax; i++) {
369 		err = scm_recv_one_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
370 		if (err < 0)
371 			break;
372 	}
373 
374 	if (i > 0) {
375 		int cmlen = CMSG_LEN(i * sizeof(int));
376 
377 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
378 		if (!err)
379 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
380 		if (!err)
381 			err = put_user(cmlen, &cm->cmsg_len);
382 		if (!err) {
383 			cmlen = CMSG_SPACE(i * sizeof(int));
384 			if (msg->msg_controllen < cmlen)
385 				cmlen = msg->msg_controllen;
386 			msg->msg_control_user += cmlen;
387 			msg->msg_controllen -= cmlen;
388 		}
389 	}
390 
391 	if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
392 		msg->msg_flags |= MSG_CTRUNC;
393 
394 	/*
395 	 * All of the files that fit in the message have had their usage counts
396 	 * incremented, so we just free the list.
397 	 */
398 	__scm_destroy(scm);
399 }
400 EXPORT_SYMBOL(scm_detach_fds);
401 
402 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
403 {
404 	struct scm_fp_list *new_fpl;
405 	int i;
406 
407 	if (!fpl)
408 		return NULL;
409 
410 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
411 			  GFP_KERNEL_ACCOUNT);
412 	if (new_fpl) {
413 		for (i = 0; i < fpl->count; i++)
414 			get_file(fpl->fp[i]);
415 
416 		new_fpl->max = new_fpl->count;
417 		new_fpl->user = get_uid(fpl->user);
418 #if IS_ENABLED(CONFIG_UNIX)
419 		new_fpl->inflight = false;
420 		new_fpl->edges = NULL;
421 		INIT_LIST_HEAD(&new_fpl->vertices);
422 #endif
423 	}
424 	return new_fpl;
425 }
426 EXPORT_SYMBOL(scm_fp_dup);
427 
428 #ifdef CONFIG_SECURITY_NETWORK
429 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
430 {
431 	struct lsm_context ctx;
432 	int err;
433 
434 	if (sk->sk_scm_security) {
435 		err = security_secid_to_secctx(scm->secid, &ctx);
436 
437 		if (err >= 0) {
438 			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, ctx.len,
439 				 ctx.context);
440 
441 			security_release_secctx(&ctx);
442 		}
443 	}
444 }
445 
446 static bool scm_has_secdata(struct sock *sk)
447 {
448 	return sk->sk_scm_security;
449 }
450 #else
451 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
452 {
453 }
454 
455 static bool scm_has_secdata(struct sock *sk)
456 {
457 	return false;
458 }
459 #endif
460 
461 static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
462 {
463 	struct file *pidfd_file = NULL;
464 	int len, pidfd;
465 
466 	/* put_cmsg() doesn't return an error if CMSG is truncated,
467 	 * that's why we need to opencode these checks here.
468 	 */
469 	if (msg->msg_flags & MSG_CMSG_COMPAT)
470 		len = sizeof(struct compat_cmsghdr) + sizeof(int);
471 	else
472 		len = sizeof(struct cmsghdr) + sizeof(int);
473 
474 	if (msg->msg_controllen < len) {
475 		msg->msg_flags |= MSG_CTRUNC;
476 		return;
477 	}
478 
479 	if (!scm->pid)
480 		return;
481 
482 	pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
483 
484 	if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
485 		if (pidfd_file) {
486 			put_unused_fd(pidfd);
487 			fput(pidfd_file);
488 		}
489 
490 		return;
491 	}
492 
493 	if (pidfd_file)
494 		fd_install(pidfd, pidfd_file);
495 }
496 
497 static bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
498 			      struct scm_cookie *scm, int flags)
499 {
500 	if (!msg->msg_control) {
501 		if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
502 		    scm->fp || scm_has_secdata(sk))
503 			msg->msg_flags |= MSG_CTRUNC;
504 
505 		scm_destroy(scm);
506 		return false;
507 	}
508 
509 	if (sk->sk_scm_credentials) {
510 		struct user_namespace *current_ns = current_user_ns();
511 		struct ucred ucreds = {
512 			.pid = scm->creds.pid,
513 			.uid = from_kuid_munged(current_ns, scm->creds.uid),
514 			.gid = from_kgid_munged(current_ns, scm->creds.gid),
515 		};
516 
517 		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
518 	}
519 
520 	scm_passec(sk, msg, scm);
521 
522 	if (scm->fp)
523 		scm_detach_fds(msg, scm);
524 
525 	return true;
526 }
527 
528 void scm_recv(struct socket *sock, struct msghdr *msg,
529 	      struct scm_cookie *scm, int flags)
530 {
531 	if (!__scm_recv_common(sock->sk, msg, scm, flags))
532 		return;
533 
534 	scm_destroy_cred(scm);
535 }
536 EXPORT_SYMBOL(scm_recv);
537 
538 void scm_recv_unix(struct socket *sock, struct msghdr *msg,
539 		   struct scm_cookie *scm, int flags)
540 {
541 	if (!__scm_recv_common(sock->sk, msg, scm, flags))
542 		return;
543 
544 	if (sock->sk->sk_scm_pidfd)
545 		scm_pidfd_recv(msg, scm);
546 
547 	scm_destroy_cred(scm);
548 }
549