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#include <linux/io_uring.h>
30
31#include <linux/uaccess.h>
32
33#include <net/protocol.h>
34#include <linux/skbuff.h>
35#include <net/sock.h>
36#include <net/compat.h>
37#include <net/scm.h>
38#include <net/cls_cgroup.h>
39#include <net/af_unix.h>
40
41
42/*
43 *	Only allow a user to send credentials, that they could set with
44 *	setu(g)id.
45 */
46
47static __inline__ int scm_check_creds(struct ucred *creds)
48{
49	const struct cred *cred = current_cred();
50	kuid_t uid = make_kuid(cred->user_ns, creds->uid);
51	kgid_t gid = make_kgid(cred->user_ns, creds->gid);
52
53	if (!uid_valid(uid) || !gid_valid(gid))
54		return -EINVAL;
55
56	if ((creds->pid == task_tgid_vnr(current) ||
57	     ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
58	    ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
59	      uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
60	    ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
61	      gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
62	       return 0;
63	}
64	return -EPERM;
65}
66
67static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
68{
69	int *fdp = (int*)CMSG_DATA(cmsg);
70	struct scm_fp_list *fpl = *fplp;
71	struct file **fpp;
72	int i, num;
73
74	num = (cmsg->cmsg_len - sizeof(struct cmsghdr))/sizeof(int);
75
76	if (num <= 0)
77		return 0;
78
79	if (num > SCM_MAX_FD)
80		return -EINVAL;
81
82	if (!fpl)
83	{
84		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL_ACCOUNT);
85		if (!fpl)
86			return -ENOMEM;
87		*fplp = fpl;
88		fpl->count = 0;
89		fpl->count_unix = 0;
90		fpl->max = SCM_MAX_FD;
91		fpl->user = NULL;
92	}
93	fpp = &fpl->fp[fpl->count];
94
95	if (fpl->count + num > fpl->max)
96		return -EINVAL;
97
98	/*
99	 *	Verify the descriptors and increment the usage count.
100	 */
101
102	for (i=0; i< num; i++)
103	{
104		int fd = fdp[i];
105		struct file *file;
106
107		if (fd < 0 || !(file = fget_raw(fd)))
108			return -EBADF;
109		/* don't allow io_uring files */
110		if (io_is_uring_fops(file)) {
111			fput(file);
112			return -EINVAL;
113		}
114		if (unix_get_socket(file))
115			fpl->count_unix++;
116
117		*fpp++ = file;
118		fpl->count++;
119	}
120
121	if (!fpl->user)
122		fpl->user = get_uid(current_user());
123
124	return num;
125}
126
127void __scm_destroy(struct scm_cookie *scm)
128{
129	struct scm_fp_list *fpl = scm->fp;
130	int i;
131
132	if (fpl) {
133		scm->fp = NULL;
134		for (i=fpl->count-1; i>=0; i--)
135			fput(fpl->fp[i]);
136		free_uid(fpl->user);
137		kfree(fpl);
138	}
139}
140EXPORT_SYMBOL(__scm_destroy);
141
142int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
143{
144	const struct proto_ops *ops = READ_ONCE(sock->ops);
145	struct cmsghdr *cmsg;
146	int err;
147
148	for_each_cmsghdr(cmsg, msg) {
149		err = -EINVAL;
150
151		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
152		/* The first check was omitted in <= 2.2.5. The reasoning was
153		   that parser checks cmsg_len in any case, so that
154		   additional check would be work duplication.
155		   But if cmsg_level is not SOL_SOCKET, we do not check
156		   for too short ancillary data object at all! Oops.
157		   OK, let's add it...
158		 */
159		if (!CMSG_OK(msg, cmsg))
160			goto error;
161
162		if (cmsg->cmsg_level != SOL_SOCKET)
163			continue;
164
165		switch (cmsg->cmsg_type)
166		{
167		case SCM_RIGHTS:
168			if (!ops || ops->family != PF_UNIX)
169				goto error;
170			err=scm_fp_copy(cmsg, &p->fp);
171			if (err<0)
172				goto error;
173			break;
174		case SCM_CREDENTIALS:
175		{
176			struct ucred creds;
177			kuid_t uid;
178			kgid_t gid;
179			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
180				goto error;
181			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
182			err = scm_check_creds(&creds);
183			if (err)
184				goto error;
185
186			p->creds.pid = creds.pid;
187			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
188				struct pid *pid;
189				err = -ESRCH;
190				pid = find_get_pid(creds.pid);
191				if (!pid)
192					goto error;
193				put_pid(p->pid);
194				p->pid = pid;
195			}
196
197			err = -EINVAL;
198			uid = make_kuid(current_user_ns(), creds.uid);
199			gid = make_kgid(current_user_ns(), creds.gid);
200			if (!uid_valid(uid) || !gid_valid(gid))
201				goto error;
202
203			p->creds.uid = uid;
204			p->creds.gid = gid;
205			break;
206		}
207		default:
208			goto error;
209		}
210	}
211
212	if (p->fp && !p->fp->count)
213	{
214		kfree(p->fp);
215		p->fp = NULL;
216	}
217	return 0;
218
219error:
220	scm_destroy(p);
221	return err;
222}
223EXPORT_SYMBOL(__scm_send);
224
225int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
226{
227	int cmlen = CMSG_LEN(len);
228
229	if (msg->msg_flags & MSG_CMSG_COMPAT)
230		return put_cmsg_compat(msg, level, type, len, data);
231
232	if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
233		msg->msg_flags |= MSG_CTRUNC;
234		return 0; /* XXX: return error? check spec. */
235	}
236	if (msg->msg_controllen < cmlen) {
237		msg->msg_flags |= MSG_CTRUNC;
238		cmlen = msg->msg_controllen;
239	}
240
241	if (msg->msg_control_is_user) {
242		struct cmsghdr __user *cm = msg->msg_control_user;
243
244		check_object_size(data, cmlen - sizeof(*cm), true);
245
246		if (!user_write_access_begin(cm, cmlen))
247			goto efault;
248
249		unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
250		unsafe_put_user(level, &cm->cmsg_level, efault_end);
251		unsafe_put_user(type, &cm->cmsg_type, efault_end);
252		unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
253				    cmlen - sizeof(*cm), efault_end);
254		user_write_access_end();
255	} else {
256		struct cmsghdr *cm = msg->msg_control;
257
258		cm->cmsg_level = level;
259		cm->cmsg_type = type;
260		cm->cmsg_len = cmlen;
261		memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
262	}
263
264	cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
265	if (msg->msg_control_is_user)
266		msg->msg_control_user += cmlen;
267	else
268		msg->msg_control += cmlen;
269	msg->msg_controllen -= cmlen;
270	return 0;
271
272efault_end:
273	user_write_access_end();
274efault:
275	return -EFAULT;
276}
277EXPORT_SYMBOL(put_cmsg);
278
279void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
280{
281	struct scm_timestamping64 tss;
282	int i;
283
284	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
285		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
286		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
287	}
288
289	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
290}
291EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
292
293void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
294{
295	struct scm_timestamping tss;
296	int i;
297
298	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
299		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
300		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
301	}
302
303	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
304}
305EXPORT_SYMBOL(put_cmsg_scm_timestamping);
306
307static int scm_max_fds(struct msghdr *msg)
308{
309	if (msg->msg_controllen <= sizeof(struct cmsghdr))
310		return 0;
311	return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
312}
313
314void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
315{
316	struct cmsghdr __user *cm =
317		(__force struct cmsghdr __user *)msg->msg_control_user;
318	unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
319	int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
320	int __user *cmsg_data = CMSG_USER_DATA(cm);
321	int err = 0, i;
322
323	/* no use for FD passing from kernel space callers */
324	if (WARN_ON_ONCE(!msg->msg_control_is_user))
325		return;
326
327	if (msg->msg_flags & MSG_CMSG_COMPAT) {
328		scm_detach_fds_compat(msg, scm);
329		return;
330	}
331
332	for (i = 0; i < fdmax; i++) {
333		err = scm_recv_one_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
334		if (err < 0)
335			break;
336	}
337
338	if (i > 0) {
339		int cmlen = CMSG_LEN(i * sizeof(int));
340
341		err = put_user(SOL_SOCKET, &cm->cmsg_level);
342		if (!err)
343			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
344		if (!err)
345			err = put_user(cmlen, &cm->cmsg_len);
346		if (!err) {
347			cmlen = CMSG_SPACE(i * sizeof(int));
348			if (msg->msg_controllen < cmlen)
349				cmlen = msg->msg_controllen;
350			msg->msg_control_user += cmlen;
351			msg->msg_controllen -= cmlen;
352		}
353	}
354
355	if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
356		msg->msg_flags |= MSG_CTRUNC;
357
358	/*
359	 * All of the files that fit in the message have had their usage counts
360	 * incremented, so we just free the list.
361	 */
362	__scm_destroy(scm);
363}
364EXPORT_SYMBOL(scm_detach_fds);
365
366struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
367{
368	struct scm_fp_list *new_fpl;
369	int i;
370
371	if (!fpl)
372		return NULL;
373
374	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
375			  GFP_KERNEL_ACCOUNT);
376	if (new_fpl) {
377		for (i = 0; i < fpl->count; i++)
378			get_file(fpl->fp[i]);
379		new_fpl->max = new_fpl->count;
380		new_fpl->user = get_uid(fpl->user);
381	}
382	return new_fpl;
383}
384EXPORT_SYMBOL(scm_fp_dup);
385