xref: /linux/net/core/scm.c (revision 260f6f4fda93c8485c8037865c941b42b9cba5d2) 
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 		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 
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 
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 
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 
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 
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 
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
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 
450 static bool scm_has_secdata(struct sock *sk)
451 {
452 	return sk->sk_scm_security;
453 }
454 #else
455 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
456 {
457 }
458 
459 static bool scm_has_secdata(struct sock *sk)
460 {
461 	return false;
462 }
463 #endif
464 
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 
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 
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 
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