xref: /openbmc/linux/net/core/scm.c (revision 84764a41) 
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/mm.h>
18 #include <linux/kernel.h>
19 #include <linux/stat.h>
20 #include <linux/socket.h>
21 #include <linux/file.h>
22 #include <linux/fcntl.h>
23 #include <linux/net.h>
24 #include <linux/interrupt.h>
25 #include <linux/netdevice.h>
26 #include <linux/security.h>
27 #include <linux/pid.h>
28 #include <linux/nsproxy.h>
29 #include <linux/slab.h>
30 
31 #include <asm/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 
39 
40 /*
41  *	Only allow a user to send credentials, that they could set with
42  *	setu(g)id.
43  */
44 
45 static __inline__ int scm_check_creds(struct ucred *creds)
46 {
47 	const struct cred *cred = current_cred();
48 	kuid_t uid = make_kuid(cred->user_ns, creds->uid);
49 	kgid_t gid = make_kgid(cred->user_ns, creds->gid);
50 
51 	if (!uid_valid(uid) || !gid_valid(gid))
52 		return -EINVAL;
53 
54 	if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
55 	    ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
56 	      uid_eq(uid, cred->suid)) || capable(CAP_SETUID)) &&
57 	    ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
58 	      gid_eq(gid, cred->sgid)) || capable(CAP_SETGID))) {
59 	       return 0;
60 	}
61 	return -EPERM;
62 }
63 
64 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
65 {
66 	int *fdp = (int*)CMSG_DATA(cmsg);
67 	struct scm_fp_list *fpl = *fplp;
68 	struct file **fpp;
69 	int i, num;
70 
71 	num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
72 
73 	if (num <= 0)
74 		return 0;
75 
76 	if (num > SCM_MAX_FD)
77 		return -EINVAL;
78 
79 	if (!fpl)
80 	{
81 		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
82 		if (!fpl)
83 			return -ENOMEM;
84 		*fplp = fpl;
85 		fpl->count = 0;
86 		fpl->max = SCM_MAX_FD;
87 	}
88 	fpp = &fpl->fp[fpl->count];
89 
90 	if (fpl->count + num > fpl->max)
91 		return -EINVAL;
92 
93 	/*
94 	 *	Verify the descriptors and increment the usage count.
95 	 */
96 
97 	for (i=0; i< num; i++)
98 	{
99 		int fd = fdp[i];
100 		struct file *file;
101 
102 		if (fd < 0 || !(file = fget_raw(fd)))
103 			return -EBADF;
104 		*fpp++ = file;
105 		fpl->count++;
106 	}
107 	return num;
108 }
109 
110 void __scm_destroy(struct scm_cookie *scm)
111 {
112 	struct scm_fp_list *fpl = scm->fp;
113 	int i;
114 
115 	if (fpl) {
116 		scm->fp = NULL;
117 		for (i=fpl->count-1; i>=0; i--)
118 			fput(fpl->fp[i]);
119 		kfree(fpl);
120 	}
121 }
122 EXPORT_SYMBOL(__scm_destroy);
123 
124 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
125 {
126 	struct cmsghdr *cmsg;
127 	int err;
128 
129 	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
130 	{
131 		err = -EINVAL;
132 
133 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
134 		/* The first check was omitted in <= 2.2.5. The reasoning was
135 		   that parser checks cmsg_len in any case, so that
136 		   additional check would be work duplication.
137 		   But if cmsg_level is not SOL_SOCKET, we do not check
138 		   for too short ancillary data object at all! Oops.
139 		   OK, let's add it...
140 		 */
141 		if (!CMSG_OK(msg, cmsg))
142 			goto error;
143 
144 		if (cmsg->cmsg_level != SOL_SOCKET)
145 			continue;
146 
147 		switch (cmsg->cmsg_type)
148 		{
149 		case SCM_RIGHTS:
150 			if (!sock->ops || sock->ops->family != PF_UNIX)
151 				goto error;
152 			err=scm_fp_copy(cmsg, &p->fp);
153 			if (err<0)
154 				goto error;
155 			break;
156 		case SCM_CREDENTIALS:
157 		{
158 			struct ucred creds;
159 			kuid_t uid;
160 			kgid_t gid;
161 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
162 				goto error;
163 			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
164 			err = scm_check_creds(&creds);
165 			if (err)
166 				goto error;
167 
168 			p->creds.pid = creds.pid;
169 			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
170 				struct pid *pid;
171 				err = -ESRCH;
172 				pid = find_get_pid(creds.pid);
173 				if (!pid)
174 					goto error;
175 				put_pid(p->pid);
176 				p->pid = pid;
177 			}
178 
179 			err = -EINVAL;
180 			uid = make_kuid(current_user_ns(), creds.uid);
181 			gid = make_kgid(current_user_ns(), creds.gid);
182 			if (!uid_valid(uid) || !gid_valid(gid))
183 				goto error;
184 
185 			p->creds.uid = uid;
186 			p->creds.gid = gid;
187 
188 			if (!p->cred ||
189 			    !uid_eq(p->cred->euid, uid) ||
190 			    !gid_eq(p->cred->egid, gid)) {
191 				struct cred *cred;
192 				err = -ENOMEM;
193 				cred = prepare_creds();
194 				if (!cred)
195 					goto error;
196 
197 				cred->uid = cred->euid = uid;
198 				cred->gid = cred->egid = gid;
199 				if (p->cred)
200 					put_cred(p->cred);
201 				p->cred = cred;
202 			}
203 			break;
204 		}
205 		default:
206 			goto error;
207 		}
208 	}
209 
210 	if (p->fp && !p->fp->count)
211 	{
212 		kfree(p->fp);
213 		p->fp = NULL;
214 	}
215 	return 0;
216 
217 error:
218 	scm_destroy(p);
219 	return err;
220 }
221 EXPORT_SYMBOL(__scm_send);
222 
223 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
224 {
225 	struct cmsghdr __user *cm
226 		= (__force struct cmsghdr __user *)msg->msg_control;
227 	struct cmsghdr cmhdr;
228 	int cmlen = CMSG_LEN(len);
229 	int err;
230 
231 	if (MSG_CMSG_COMPAT & msg->msg_flags)
232 		return put_cmsg_compat(msg, level, type, len, data);
233 
234 	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
235 		msg->msg_flags |= MSG_CTRUNC;
236 		return 0; /* XXX: return error? check spec. */
237 	}
238 	if (msg->msg_controllen < cmlen) {
239 		msg->msg_flags |= MSG_CTRUNC;
240 		cmlen = msg->msg_controllen;
241 	}
242 	cmhdr.cmsg_level = level;
243 	cmhdr.cmsg_type = type;
244 	cmhdr.cmsg_len = cmlen;
245 
246 	err = -EFAULT;
247 	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
248 		goto out;
249 	if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
250 		goto out;
251 	cmlen = CMSG_SPACE(len);
252 	if (msg->msg_controllen < cmlen)
253 		cmlen = msg->msg_controllen;
254 	msg->msg_control += cmlen;
255 	msg->msg_controllen -= cmlen;
256 	err = 0;
257 out:
258 	return err;
259 }
260 EXPORT_SYMBOL(put_cmsg);
261 
262 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
263 {
264 	struct cmsghdr __user *cm
265 		= (__force struct cmsghdr __user*)msg->msg_control;
266 
267 	int fdmax = 0;
268 	int fdnum = scm->fp->count;
269 	struct file **fp = scm->fp->fp;
270 	int __user *cmfptr;
271 	int err = 0, i;
272 
273 	if (MSG_CMSG_COMPAT & msg->msg_flags) {
274 		scm_detach_fds_compat(msg, scm);
275 		return;
276 	}
277 
278 	if (msg->msg_controllen > sizeof(struct cmsghdr))
279 		fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
280 			 / sizeof(int));
281 
282 	if (fdnum < fdmax)
283 		fdmax = fdnum;
284 
285 	for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
286 	     i++, cmfptr++)
287 	{
288 		struct socket *sock;
289 		int new_fd;
290 		err = security_file_receive(fp[i]);
291 		if (err)
292 			break;
293 		err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
294 					  ? O_CLOEXEC : 0);
295 		if (err < 0)
296 			break;
297 		new_fd = err;
298 		err = put_user(new_fd, cmfptr);
299 		if (err) {
300 			put_unused_fd(new_fd);
301 			break;
302 		}
303 		/* Bump the usage count and install the file. */
304 		sock = sock_from_file(fp[i], &err);
305 		if (sock)
306 			sock_update_netprioidx(sock->sk, current);
307 		fd_install(new_fd, get_file(fp[i]));
308 	}
309 
310 	if (i > 0)
311 	{
312 		int cmlen = CMSG_LEN(i*sizeof(int));
313 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
314 		if (!err)
315 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
316 		if (!err)
317 			err = put_user(cmlen, &cm->cmsg_len);
318 		if (!err) {
319 			cmlen = CMSG_SPACE(i*sizeof(int));
320 			msg->msg_control += cmlen;
321 			msg->msg_controllen -= cmlen;
322 		}
323 	}
324 	if (i < fdnum || (fdnum && fdmax <= 0))
325 		msg->msg_flags |= MSG_CTRUNC;
326 
327 	/*
328 	 * All of the files that fit in the message have had their
329 	 * usage counts incremented, so we just free the list.
330 	 */
331 	__scm_destroy(scm);
332 }
333 EXPORT_SYMBOL(scm_detach_fds);
334 
335 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
336 {
337 	struct scm_fp_list *new_fpl;
338 	int i;
339 
340 	if (!fpl)
341 		return NULL;
342 
343 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
344 			  GFP_KERNEL);
345 	if (new_fpl) {
346 		for (i = 0; i < fpl->count; i++)
347 			get_file(fpl->fp[i]);
348 		new_fpl->max = new_fpl->count;
349 	}
350 	return new_fpl;
351 }
352 EXPORT_SYMBOL(scm_fp_dup);
353