xref: /linux/net/core/scm.c (revision 860a9bed265146b10311bcadbbcef59c3af4454d) 
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 
47 static __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 
67 static 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 #if IS_ENABLED(CONFIG_UNIX)
93 		fpl->inflight = false;
94 		fpl->edges = NULL;
95 		INIT_LIST_HEAD(&fpl->vertices);
96 #endif
97 	}
98 	fpp = &fpl->fp[fpl->count];
99 
100 	if (fpl->count + num > fpl->max)
101 		return -EINVAL;
102 
103 	/*
104 	 *	Verify the descriptors and increment the usage count.
105 	 */
106 
107 	for (i=0; i< num; i++)
108 	{
109 		int fd = fdp[i];
110 		struct file *file;
111 
112 		if (fd < 0 || !(file = fget_raw(fd)))
113 			return -EBADF;
114 		/* don't allow io_uring files */
115 		if (io_is_uring_fops(file)) {
116 			fput(file);
117 			return -EINVAL;
118 		}
119 		if (unix_get_socket(file))
120 			fpl->count_unix++;
121 
122 		*fpp++ = file;
123 		fpl->count++;
124 	}
125 
126 	if (!fpl->user)
127 		fpl->user = get_uid(current_user());
128 
129 	return num;
130 }
131 
132 void __scm_destroy(struct scm_cookie *scm)
133 {
134 	struct scm_fp_list *fpl = scm->fp;
135 	int i;
136 
137 	if (fpl) {
138 		scm->fp = NULL;
139 		for (i=fpl->count-1; i>=0; i--)
140 			fput(fpl->fp[i]);
141 		free_uid(fpl->user);
142 		kfree(fpl);
143 	}
144 }
145 EXPORT_SYMBOL(__scm_destroy);
146 
147 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
148 {
149 	const struct proto_ops *ops = READ_ONCE(sock->ops);
150 	struct cmsghdr *cmsg;
151 	int err;
152 
153 	for_each_cmsghdr(cmsg, msg) {
154 		err = -EINVAL;
155 
156 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
157 		/* The first check was omitted in <= 2.2.5. The reasoning was
158 		   that parser checks cmsg_len in any case, so that
159 		   additional check would be work duplication.
160 		   But if cmsg_level is not SOL_SOCKET, we do not check
161 		   for too short ancillary data object at all! Oops.
162 		   OK, let's add it...
163 		 */
164 		if (!CMSG_OK(msg, cmsg))
165 			goto error;
166 
167 		if (cmsg->cmsg_level != SOL_SOCKET)
168 			continue;
169 
170 		switch (cmsg->cmsg_type)
171 		{
172 		case SCM_RIGHTS:
173 			if (!ops || ops->family != PF_UNIX)
174 				goto error;
175 			err=scm_fp_copy(cmsg, &p->fp);
176 			if (err<0)
177 				goto error;
178 			break;
179 		case SCM_CREDENTIALS:
180 		{
181 			struct ucred creds;
182 			kuid_t uid;
183 			kgid_t gid;
184 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
185 				goto error;
186 			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
187 			err = scm_check_creds(&creds);
188 			if (err)
189 				goto error;
190 
191 			p->creds.pid = creds.pid;
192 			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
193 				struct pid *pid;
194 				err = -ESRCH;
195 				pid = find_get_pid(creds.pid);
196 				if (!pid)
197 					goto error;
198 				put_pid(p->pid);
199 				p->pid = pid;
200 			}
201 
202 			err = -EINVAL;
203 			uid = make_kuid(current_user_ns(), creds.uid);
204 			gid = make_kgid(current_user_ns(), creds.gid);
205 			if (!uid_valid(uid) || !gid_valid(gid))
206 				goto error;
207 
208 			p->creds.uid = uid;
209 			p->creds.gid = gid;
210 			break;
211 		}
212 		default:
213 			goto error;
214 		}
215 	}
216 
217 	if (p->fp && !p->fp->count)
218 	{
219 		kfree(p->fp);
220 		p->fp = NULL;
221 	}
222 	return 0;
223 
224 error:
225 	scm_destroy(p);
226 	return err;
227 }
228 EXPORT_SYMBOL(__scm_send);
229 
230 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
231 {
232 	int cmlen = CMSG_LEN(len);
233 
234 	if (msg->msg_flags & MSG_CMSG_COMPAT)
235 		return put_cmsg_compat(msg, level, type, len, data);
236 
237 	if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
238 		msg->msg_flags |= MSG_CTRUNC;
239 		return 0; /* XXX: return error? check spec. */
240 	}
241 	if (msg->msg_controllen < cmlen) {
242 		msg->msg_flags |= MSG_CTRUNC;
243 		cmlen = msg->msg_controllen;
244 	}
245 
246 	if (msg->msg_control_is_user) {
247 		struct cmsghdr __user *cm = msg->msg_control_user;
248 
249 		check_object_size(data, cmlen - sizeof(*cm), true);
250 
251 		if (!user_write_access_begin(cm, cmlen))
252 			goto efault;
253 
254 		unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
255 		unsafe_put_user(level, &cm->cmsg_level, efault_end);
256 		unsafe_put_user(type, &cm->cmsg_type, efault_end);
257 		unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
258 				    cmlen - sizeof(*cm), efault_end);
259 		user_write_access_end();
260 	} else {
261 		struct cmsghdr *cm = msg->msg_control;
262 
263 		cm->cmsg_level = level;
264 		cm->cmsg_type = type;
265 		cm->cmsg_len = cmlen;
266 		memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
267 	}
268 
269 	cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
270 	if (msg->msg_control_is_user)
271 		msg->msg_control_user += cmlen;
272 	else
273 		msg->msg_control += cmlen;
274 	msg->msg_controllen -= cmlen;
275 	return 0;
276 
277 efault_end:
278 	user_write_access_end();
279 efault:
280 	return -EFAULT;
281 }
282 EXPORT_SYMBOL(put_cmsg);
283 
284 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
285 {
286 	struct scm_timestamping64 tss;
287 	int i;
288 
289 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
290 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
291 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
292 	}
293 
294 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
295 }
296 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
297 
298 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
299 {
300 	struct scm_timestamping tss;
301 	int i;
302 
303 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
304 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
305 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
306 	}
307 
308 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
309 }
310 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
311 
312 static int scm_max_fds(struct msghdr *msg)
313 {
314 	if (msg->msg_controllen <= sizeof(struct cmsghdr))
315 		return 0;
316 	return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
317 }
318 
319 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
320 {
321 	struct cmsghdr __user *cm =
322 		(__force struct cmsghdr __user *)msg->msg_control_user;
323 	unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
324 	int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
325 	int __user *cmsg_data = CMSG_USER_DATA(cm);
326 	int err = 0, i;
327 
328 	/* no use for FD passing from kernel space callers */
329 	if (WARN_ON_ONCE(!msg->msg_control_is_user))
330 		return;
331 
332 	if (msg->msg_flags & MSG_CMSG_COMPAT) {
333 		scm_detach_fds_compat(msg, scm);
334 		return;
335 	}
336 
337 	for (i = 0; i < fdmax; i++) {
338 		err = scm_recv_one_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
339 		if (err < 0)
340 			break;
341 	}
342 
343 	if (i > 0) {
344 		int cmlen = CMSG_LEN(i * sizeof(int));
345 
346 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
347 		if (!err)
348 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
349 		if (!err)
350 			err = put_user(cmlen, &cm->cmsg_len);
351 		if (!err) {
352 			cmlen = CMSG_SPACE(i * sizeof(int));
353 			if (msg->msg_controllen < cmlen)
354 				cmlen = msg->msg_controllen;
355 			msg->msg_control_user += cmlen;
356 			msg->msg_controllen -= cmlen;
357 		}
358 	}
359 
360 	if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
361 		msg->msg_flags |= MSG_CTRUNC;
362 
363 	/*
364 	 * All of the files that fit in the message have had their usage counts
365 	 * incremented, so we just free the list.
366 	 */
367 	__scm_destroy(scm);
368 }
369 EXPORT_SYMBOL(scm_detach_fds);
370 
371 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
372 {
373 	struct scm_fp_list *new_fpl;
374 	int i;
375 
376 	if (!fpl)
377 		return NULL;
378 
379 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
380 			  GFP_KERNEL_ACCOUNT);
381 	if (new_fpl) {
382 		for (i = 0; i < fpl->count; i++)
383 			get_file(fpl->fp[i]);
384 
385 		new_fpl->max = new_fpl->count;
386 		new_fpl->user = get_uid(fpl->user);
387 #if IS_ENABLED(CONFIG_UNIX)
388 		new_fpl->inflight = false;
389 		new_fpl->edges = NULL;
390 		INIT_LIST_HEAD(&new_fpl->vertices);
391 #endif
392 	}
393 	return new_fpl;
394 }
395 EXPORT_SYMBOL(scm_fp_dup);
396