xref: /openbmc/linux/net/core/scm.c (revision f9a82c48) 
1 /* scm.c - Socket level control messages processing.
2  *
3  * Author:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
4  *              Alignment and value checking mods by Craig Metz
5  *
6  *		This program is free software; you can redistribute it and/or
7  *		modify it under the terms of the GNU General Public License
8  *		as published by the Free Software Foundation; either version
9  *		2 of the License, or (at your option) any later version.
10  */
11 
12 #include <linux/module.h>
13 #include <linux/signal.h>
14 #include <linux/capability.h>
15 #include <linux/errno.h>
16 #include <linux/sched.h>
17 #include <linux/sched/user.h>
18 #include <linux/mm.h>
19 #include <linux/kernel.h>
20 #include <linux/stat.h>
21 #include <linux/socket.h>
22 #include <linux/file.h>
23 #include <linux/fcntl.h>
24 #include <linux/net.h>
25 #include <linux/interrupt.h>
26 #include <linux/netdevice.h>
27 #include <linux/security.h>
28 #include <linux/pid_namespace.h>
29 #include <linux/pid.h>
30 #include <linux/nsproxy.h>
31 #include <linux/slab.h>
32 #include <linux/errqueue.h>
33 
34 #include <linux/uaccess.h>
35 
36 #include <net/protocol.h>
37 #include <linux/skbuff.h>
38 #include <net/sock.h>
39 #include <net/compat.h>
40 #include <net/scm.h>
41 #include <net/cls_cgroup.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);
87 		if (!fpl)
88 			return -ENOMEM;
89 		*fplp = fpl;
90 		fpl->count = 0;
91 		fpl->max = SCM_MAX_FD;
92 		fpl->user = NULL;
93 	}
94 	fpp = &fpl->fp[fpl->count];
95 
96 	if (fpl->count + num > fpl->max)
97 		return -EINVAL;
98 
99 	/*
100 	 *	Verify the descriptors and increment the usage count.
101 	 */
102 
103 	for (i=0; i< num; i++)
104 	{
105 		int fd = fdp[i];
106 		struct file *file;
107 
108 		if (fd < 0 || !(file = fget_raw(fd)))
109 			return -EBADF;
110 		*fpp++ = file;
111 		fpl->count++;
112 	}
113 
114 	if (!fpl->user)
115 		fpl->user = get_uid(current_user());
116 
117 	return num;
118 }
119 
120 void __scm_destroy(struct scm_cookie *scm)
121 {
122 	struct scm_fp_list *fpl = scm->fp;
123 	int i;
124 
125 	if (fpl) {
126 		scm->fp = NULL;
127 		for (i=fpl->count-1; i>=0; i--)
128 			fput(fpl->fp[i]);
129 		free_uid(fpl->user);
130 		kfree(fpl);
131 	}
132 }
133 EXPORT_SYMBOL(__scm_destroy);
134 
135 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
136 {
137 	struct cmsghdr *cmsg;
138 	int err;
139 
140 	for_each_cmsghdr(cmsg, msg) {
141 		err = -EINVAL;
142 
143 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
144 		/* The first check was omitted in <= 2.2.5. The reasoning was
145 		   that parser checks cmsg_len in any case, so that
146 		   additional check would be work duplication.
147 		   But if cmsg_level is not SOL_SOCKET, we do not check
148 		   for too short ancillary data object at all! Oops.
149 		   OK, let's add it...
150 		 */
151 		if (!CMSG_OK(msg, cmsg))
152 			goto error;
153 
154 		if (cmsg->cmsg_level != SOL_SOCKET)
155 			continue;
156 
157 		switch (cmsg->cmsg_type)
158 		{
159 		case SCM_RIGHTS:
160 			if (!sock->ops || sock->ops->family != PF_UNIX)
161 				goto error;
162 			err=scm_fp_copy(cmsg, &p->fp);
163 			if (err<0)
164 				goto error;
165 			break;
166 		case SCM_CREDENTIALS:
167 		{
168 			struct ucred creds;
169 			kuid_t uid;
170 			kgid_t gid;
171 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
172 				goto error;
173 			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
174 			err = scm_check_creds(&creds);
175 			if (err)
176 				goto error;
177 
178 			p->creds.pid = creds.pid;
179 			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
180 				struct pid *pid;
181 				err = -ESRCH;
182 				pid = find_get_pid(creds.pid);
183 				if (!pid)
184 					goto error;
185 				put_pid(p->pid);
186 				p->pid = pid;
187 			}
188 
189 			err = -EINVAL;
190 			uid = make_kuid(current_user_ns(), creds.uid);
191 			gid = make_kgid(current_user_ns(), creds.gid);
192 			if (!uid_valid(uid) || !gid_valid(gid))
193 				goto error;
194 
195 			p->creds.uid = uid;
196 			p->creds.gid = gid;
197 			break;
198 		}
199 		default:
200 			goto error;
201 		}
202 	}
203 
204 	if (p->fp && !p->fp->count)
205 	{
206 		kfree(p->fp);
207 		p->fp = NULL;
208 	}
209 	return 0;
210 
211 error:
212 	scm_destroy(p);
213 	return err;
214 }
215 EXPORT_SYMBOL(__scm_send);
216 
217 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
218 {
219 	struct cmsghdr __user *cm
220 		= (__force struct cmsghdr __user *)msg->msg_control;
221 	struct cmsghdr cmhdr;
222 	int cmlen = CMSG_LEN(len);
223 	int err;
224 
225 	if (MSG_CMSG_COMPAT & msg->msg_flags)
226 		return put_cmsg_compat(msg, level, type, len, data);
227 
228 	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
229 		msg->msg_flags |= MSG_CTRUNC;
230 		return 0; /* XXX: return error? check spec. */
231 	}
232 	if (msg->msg_controllen < cmlen) {
233 		msg->msg_flags |= MSG_CTRUNC;
234 		cmlen = msg->msg_controllen;
235 	}
236 	cmhdr.cmsg_level = level;
237 	cmhdr.cmsg_type = type;
238 	cmhdr.cmsg_len = cmlen;
239 
240 	err = -EFAULT;
241 	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
242 		goto out;
243 	if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
244 		goto out;
245 	cmlen = CMSG_SPACE(len);
246 	if (msg->msg_controllen < cmlen)
247 		cmlen = msg->msg_controllen;
248 	msg->msg_control += cmlen;
249 	msg->msg_controllen -= cmlen;
250 	err = 0;
251 out:
252 	return err;
253 }
254 EXPORT_SYMBOL(put_cmsg);
255 
256 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
257 {
258 	struct scm_timestamping64 tss;
259 	int i;
260 
261 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
262 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
263 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
264 	}
265 
266 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
267 }
268 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
269 
270 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
271 {
272 	struct scm_timestamping tss;
273 	int i;
274 
275 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++)
276 		tss.ts[i] = timespec64_to_timespec(tss_internal->ts[i]);
277 
278 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
279 }
280 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
281 
282 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
283 {
284 	struct cmsghdr __user *cm
285 		= (__force struct cmsghdr __user*)msg->msg_control;
286 
287 	int fdmax = 0;
288 	int fdnum = scm->fp->count;
289 	struct file **fp = scm->fp->fp;
290 	int __user *cmfptr;
291 	int err = 0, i;
292 
293 	if (MSG_CMSG_COMPAT & msg->msg_flags) {
294 		scm_detach_fds_compat(msg, scm);
295 		return;
296 	}
297 
298 	if (msg->msg_controllen > sizeof(struct cmsghdr))
299 		fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
300 			 / sizeof(int));
301 
302 	if (fdnum < fdmax)
303 		fdmax = fdnum;
304 
305 	for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
306 	     i++, cmfptr++)
307 	{
308 		struct socket *sock;
309 		int new_fd;
310 		err = security_file_receive(fp[i]);
311 		if (err)
312 			break;
313 		err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
314 					  ? O_CLOEXEC : 0);
315 		if (err < 0)
316 			break;
317 		new_fd = err;
318 		err = put_user(new_fd, cmfptr);
319 		if (err) {
320 			put_unused_fd(new_fd);
321 			break;
322 		}
323 		/* Bump the usage count and install the file. */
324 		sock = sock_from_file(fp[i], &err);
325 		if (sock) {
326 			sock_update_netprioidx(&sock->sk->sk_cgrp_data);
327 			sock_update_classid(&sock->sk->sk_cgrp_data);
328 		}
329 		fd_install(new_fd, get_file(fp[i]));
330 	}
331 
332 	if (i > 0)
333 	{
334 		int cmlen = CMSG_LEN(i*sizeof(int));
335 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
336 		if (!err)
337 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
338 		if (!err)
339 			err = put_user(cmlen, &cm->cmsg_len);
340 		if (!err) {
341 			cmlen = CMSG_SPACE(i*sizeof(int));
342 			if (msg->msg_controllen < cmlen)
343 				cmlen = msg->msg_controllen;
344 			msg->msg_control += cmlen;
345 			msg->msg_controllen -= cmlen;
346 		}
347 	}
348 	if (i < fdnum || (fdnum && fdmax <= 0))
349 		msg->msg_flags |= MSG_CTRUNC;
350 
351 	/*
352 	 * All of the files that fit in the message have had their
353 	 * usage counts incremented, so we just free the list.
354 	 */
355 	__scm_destroy(scm);
356 }
357 EXPORT_SYMBOL(scm_detach_fds);
358 
359 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
360 {
361 	struct scm_fp_list *new_fpl;
362 	int i;
363 
364 	if (!fpl)
365 		return NULL;
366 
367 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
368 			  GFP_KERNEL);
369 	if (new_fpl) {
370 		for (i = 0; i < fpl->count; i++)
371 			get_file(fpl->fp[i]);
372 		new_fpl->max = new_fpl->count;
373 		new_fpl->user = get_uid(fpl->user);
374 	}
375 	return new_fpl;
376 }
377 EXPORT_SYMBOL(scm_fp_dup);
378