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_obj(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 struct pid *thread_pid;
153 int err;
154
155 /* drop all previous references */
156 scm_destroy_cred(scm);
157
158 err = pidfs_register_pid(pid);
159 if (unlikely(err))
160 return err;
161
162 /* A sender naming its own thread-group sends from the current thread. */
163 if (pid == task_tgid(current))
164 thread_pid = task_pid(current);
165 else
166 thread_pid = pid;
167
168 err = pidfs_register_pid(thread_pid);
169 if (unlikely(err))
170 return err;
171
172 scm->pid[PIDTYPE_TGID] = pid;
173 scm->pid[PIDTYPE_PID] = get_pid(thread_pid);
174 scm->creds.pid = pid_vnr(pid);
175 return 0;
176 }
177
__scm_send(struct socket * sock,struct msghdr * msg,struct scm_cookie * p)178 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
179 {
180 const struct proto_ops *ops = READ_ONCE(sock->ops);
181 struct cmsghdr *cmsg;
182 int err;
183
184 for_each_cmsghdr(cmsg, msg) {
185 err = -EINVAL;
186
187 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
188 /* The first check was omitted in <= 2.2.5. The reasoning was
189 that parser checks cmsg_len in any case, so that
190 additional check would be work duplication.
191 But if cmsg_level is not SOL_SOCKET, we do not check
192 for too short ancillary data object at all! Oops.
193 OK, let's add it...
194 */
195 if (!CMSG_OK(msg, cmsg))
196 goto error;
197
198 if (cmsg->cmsg_level != SOL_SOCKET)
199 continue;
200
201 switch (cmsg->cmsg_type)
202 {
203 case SCM_RIGHTS:
204 if (!ops || ops->family != PF_UNIX)
205 goto error;
206 err=scm_fp_copy(cmsg, &p->fp);
207 if (err<0)
208 goto error;
209 break;
210 case SCM_CREDENTIALS:
211 {
212 struct ucred creds;
213 kuid_t uid;
214 kgid_t gid;
215 if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
216 goto error;
217 memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
218 err = scm_check_creds(&creds);
219 if (err)
220 goto error;
221
222 if (!p->pid[PIDTYPE_TGID] ||
223 pid_vnr(p->pid[PIDTYPE_TGID]) != creds.pid) {
224 struct pid *pid;
225 err = -ESRCH;
226 pid = find_get_pid(creds.pid);
227 if (!pid)
228 goto error;
229
230 /* pass a struct pid reference from
231 * find_get_pid() to scm_replace_pid().
232 */
233 err = scm_replace_pid(p, pid);
234 if (err) {
235 put_pid(pid);
236 goto error;
237 }
238 }
239
240 err = -EINVAL;
241 uid = make_kuid(current_user_ns(), creds.uid);
242 gid = make_kgid(current_user_ns(), creds.gid);
243 if (!uid_valid(uid) || !gid_valid(gid))
244 goto error;
245
246 p->creds.uid = uid;
247 p->creds.gid = gid;
248 break;
249 }
250 default:
251 goto error;
252 }
253 }
254
255 if (p->fp && !p->fp->count)
256 {
257 kfree(p->fp);
258 p->fp = NULL;
259 }
260 return 0;
261
262 error:
263 scm_destroy(p);
264 return err;
265 }
266 EXPORT_SYMBOL(__scm_send);
267
put_cmsg(struct msghdr * msg,int level,int type,int len,void * data)268 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
269 {
270 int cmlen = CMSG_LEN(len);
271
272 if (msg->msg_flags & MSG_CMSG_COMPAT)
273 return put_cmsg_compat(msg, level, type, len, data);
274
275 if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
276 msg->msg_flags |= MSG_CTRUNC;
277 return 0; /* XXX: return error? check spec. */
278 }
279 if (msg->msg_controllen < cmlen) {
280 msg->msg_flags |= MSG_CTRUNC;
281 cmlen = msg->msg_controllen;
282 }
283
284 if (msg->msg_control_is_user) {
285 struct cmsghdr __user *cm = msg->msg_control_user;
286
287 check_object_size(data, cmlen - sizeof(*cm), true);
288
289 scoped_user_write_access_size(cm, cmlen, efault) {
290 unsafe_put_user(cmlen, &cm->cmsg_len, efault);
291 unsafe_put_user(level, &cm->cmsg_level, efault);
292 unsafe_put_user(type, &cm->cmsg_type, efault);
293 unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
294 cmlen - sizeof(*cm), efault);
295 }
296 } else {
297 struct cmsghdr *cm = msg->msg_control;
298
299 cm->cmsg_level = level;
300 cm->cmsg_type = type;
301 cm->cmsg_len = cmlen;
302 memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
303 }
304
305 cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
306 if (msg->msg_control_is_user)
307 msg->msg_control_user += cmlen;
308 else
309 msg->msg_control += cmlen;
310 msg->msg_controllen -= cmlen;
311 return 0;
312
313 efault:
314 return -EFAULT;
315 }
316 EXPORT_SYMBOL(put_cmsg);
317
put_cmsg_notrunc(struct msghdr * msg,int level,int type,int len,void * data)318 int put_cmsg_notrunc(struct msghdr *msg, int level, int type, int len,
319 void *data)
320 {
321 /* Don't produce truncated CMSGs */
322 if (!msg->msg_control || msg->msg_controllen < CMSG_LEN(len))
323 return -ETOOSMALL;
324
325 return put_cmsg(msg, level, type, len, data);
326 }
327
put_cmsg_scm_timestamping64(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)328 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
329 {
330 struct scm_timestamping64 tss;
331 int i;
332
333 for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
334 struct timespec64 tv = ktime_to_timespec64(tss_internal->ts[i]);
335
336 tss.ts[i].tv_sec = tv.tv_sec;
337 tss.ts[i].tv_nsec = tv.tv_nsec;
338 }
339
340 put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
341 }
342 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
343
put_cmsg_scm_timestamping(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)344 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
345 {
346 struct scm_timestamping tss;
347 int i;
348
349 for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
350 struct timespec64 tv = ktime_to_timespec64(tss_internal->ts[i]);
351
352 tss.ts[i].tv_sec = tv.tv_sec;
353 tss.ts[i].tv_nsec = tv.tv_nsec;
354 }
355
356 put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
357 }
358 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
359
scm_max_fds(struct msghdr * msg)360 static int scm_max_fds(struct msghdr *msg)
361 {
362 if (msg->msg_controllen <= sizeof(struct cmsghdr))
363 return 0;
364 return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
365 }
366
scm_recv_one_fd(struct file * f,int __user * ufd,unsigned int flags,bool notrunc)367 int scm_recv_one_fd(struct file *f, int __user *ufd, unsigned int flags,
368 bool notrunc)
369 {
370 int error;
371
372 if (!ufd)
373 return -EFAULT;
374
375 error = security_file_receive(f);
376 if (error)
377 return notrunc ? put_user(error, ufd) : error;
378
379 FD_PREPARE(fdf, flags, get_file(f));
380 if (fdf->fd < 0)
381 return fdf->fd;
382
383 error = put_user(fdf->fd, ufd);
384 if (error)
385 return error;
386
387 __receive_sock(fdf->file);
388 return fd_publish(fdf);
389 }
390
scm_detach_fds(struct msghdr * msg,struct scm_cookie * scm,bool notrunc)391 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm, bool notrunc)
392 {
393 struct cmsghdr __user *cm =
394 (__force struct cmsghdr __user *)msg->msg_control_user;
395 unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
396 int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
397 int __user *cmsg_data = CMSG_USER_DATA(cm);
398 int err = 0, i;
399
400 /* no use for FD passing from kernel space callers */
401 if (WARN_ON_ONCE(!msg->msg_control_is_user))
402 return;
403
404 if (msg->msg_flags & MSG_CMSG_COMPAT) {
405 scm_detach_fds_compat(msg, scm, notrunc);
406 return;
407 }
408
409 for (i = 0; i < fdmax; i++) {
410 err = scm_recv_one_fd(scm->fp->fp[i], cmsg_data + i, o_flags, notrunc);
411 if (err < 0)
412 break;
413 }
414
415 if (i > 0) {
416 int cmlen = CMSG_LEN(i * sizeof(int));
417
418 err = put_user(SOL_SOCKET, &cm->cmsg_level);
419 if (!err)
420 err = put_user(SCM_RIGHTS, &cm->cmsg_type);
421 if (!err)
422 err = put_user(cmlen, &cm->cmsg_len);
423 if (!err) {
424 cmlen = CMSG_SPACE(i * sizeof(int));
425 if (msg->msg_controllen < cmlen)
426 cmlen = msg->msg_controllen;
427 msg->msg_control_user += cmlen;
428 msg->msg_controllen -= cmlen;
429 }
430 }
431
432 if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
433 msg->msg_flags |= MSG_CTRUNC;
434
435 /*
436 * All of the files that fit in the message have had their usage counts
437 * incremented, so we just free the list.
438 */
439 __scm_destroy(scm);
440 }
441 EXPORT_SYMBOL(scm_detach_fds);
442
scm_fp_dup(struct scm_fp_list * fpl)443 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
444 {
445 struct scm_fp_list *new_fpl;
446 int i;
447
448 if (!fpl)
449 return NULL;
450
451 new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
452 GFP_KERNEL_ACCOUNT);
453 if (new_fpl) {
454 for (i = 0; i < fpl->count; i++)
455 get_file(fpl->fp[i]);
456
457 new_fpl->max = new_fpl->count;
458 new_fpl->user = get_uid(fpl->user);
459 #if IS_ENABLED(CONFIG_UNIX)
460 new_fpl->inflight = false;
461 new_fpl->edges = NULL;
462 INIT_LIST_HEAD(&new_fpl->vertices);
463 #endif
464 }
465 return new_fpl;
466 }
467 EXPORT_SYMBOL(scm_fp_dup);
468
469 #ifdef CONFIG_SECURITY_NETWORK
scm_passec(struct sock * sk,struct msghdr * msg,struct scm_cookie * scm)470 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
471 {
472 struct lsm_context ctx;
473 int err;
474
475 if (sk->sk_scm_security) {
476 err = security_secid_to_secctx(scm->secid, &ctx);
477
478 if (err >= 0) {
479 put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, ctx.len,
480 ctx.context);
481
482 security_release_secctx(&ctx);
483 }
484 }
485 }
486
scm_has_secdata(struct sock * sk)487 static bool scm_has_secdata(struct sock *sk)
488 {
489 return sk->sk_scm_security;
490 }
491 #else
scm_passec(struct sock * sk,struct msghdr * msg,struct scm_cookie * scm)492 static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
493 {
494 }
495
scm_has_secdata(struct sock * sk)496 static bool scm_has_secdata(struct sock *sk)
497 {
498 return false;
499 }
500 #endif
501
scm_pidfd_recv(struct msghdr * msg,struct scm_cookie * scm,enum pid_type type,int cmsg_type)502 static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm,
503 enum pid_type type, int cmsg_type)
504 {
505 unsigned int flags = PIDFD_STALE;
506 struct file *pidfd_file = NULL;
507 struct pid *pid;
508 int len, pidfd;
509
510 pid = scm->pid[type];
511
512 /* put_cmsg() doesn't return an error if CMSG is truncated,
513 * that's why we need to opencode these checks here.
514 */
515 if (msg->msg_flags & MSG_CMSG_COMPAT)
516 len = sizeof(struct compat_cmsghdr) + sizeof(int);
517 else
518 len = sizeof(struct cmsghdr) + sizeof(int);
519
520 if (msg->msg_controllen < len) {
521 msg->msg_flags |= MSG_CTRUNC;
522 return;
523 }
524
525 if (!pid)
526 return;
527
528 if (type == PIDTYPE_PID)
529 flags |= PIDFD_THREAD;
530
531 pidfd = pidfd_prepare(pid, flags, &pidfd_file);
532
533 if (put_cmsg(msg, SOL_SOCKET, cmsg_type, sizeof(int), &pidfd)) {
534 if (pidfd_file) {
535 put_unused_fd(pidfd);
536 fput(pidfd_file);
537 }
538
539 return;
540 }
541
542 if (pidfd_file)
543 fd_install(pidfd, pidfd_file);
544 }
545
__scm_recv_common(struct sock * sk,struct msghdr * msg,struct scm_cookie * scm,int flags)546 static bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
547 struct scm_cookie *scm, int flags)
548 {
549 if (!msg->msg_control) {
550 if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
551 sk->sk_scm_pidfd_thread || scm->fp || scm_has_secdata(sk))
552 msg->msg_flags |= MSG_CTRUNC;
553
554 scm_destroy(scm);
555 return false;
556 }
557
558 if (sk->sk_scm_credentials) {
559 struct user_namespace *current_ns = current_user_ns();
560 struct ucred ucreds = {
561 .pid = scm->creds.pid,
562 .uid = from_kuid_munged(current_ns, scm->creds.uid),
563 .gid = from_kgid_munged(current_ns, scm->creds.gid),
564 };
565
566 put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
567 }
568
569 scm_passec(sk, msg, scm);
570
571 return true;
572 }
573
scm_recv(struct socket * sock,struct msghdr * msg,struct scm_cookie * scm,int flags)574 void scm_recv(struct socket *sock, struct msghdr *msg,
575 struct scm_cookie *scm, int flags)
576 {
577 if (!__scm_recv_common(sock->sk, msg, scm, flags))
578 return;
579
580 scm_destroy_cred(scm);
581 }
582 EXPORT_SYMBOL(scm_recv);
583
scm_recv_unix(struct socket * sock,struct msghdr * msg,struct scm_cookie * scm,int flags)584 void scm_recv_unix(struct socket *sock, struct msghdr *msg,
585 struct scm_cookie *scm, int flags)
586 {
587 if (!__scm_recv_common(sock->sk, msg, scm, flags))
588 return;
589
590 if (scm->fp) {
591 struct unix_sock *u;
592
593 u = unix_sk(sock->sk);
594 scm_detach_fds(msg, scm, READ_ONCE(u->scm_rights_notrunc));
595 }
596
597 if (sock->sk->sk_scm_pidfd)
598 scm_pidfd_recv(msg, scm, PIDTYPE_TGID, SCM_PIDFD);
599
600 if (sock->sk->sk_scm_pidfd_thread)
601 scm_pidfd_recv(msg, scm, PIDTYPE_PID, SCM_PIDFD_THREAD);
602
603 scm_destroy_cred(scm);
604 }
605