xref: /openbmc/linux/net/core/scm.c (revision 9d749629) 
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 #include <net/cls_cgroup.h>
39 
40 
41 /*
42  *	Only allow a user to send credentials, that they could set with
43  *	setu(g)id.
44  */
45 
46 static __inline__ int scm_check_creds(struct ucred *creds)
47 {
48 	const struct cred *cred = current_cred();
49 	kuid_t uid = make_kuid(cred->user_ns, creds->uid);
50 	kgid_t gid = make_kgid(cred->user_ns, creds->gid);
51 
52 	if (!uid_valid(uid) || !gid_valid(gid))
53 		return -EINVAL;
54 
55 	if ((creds->pid == task_tgid_vnr(current) || nsown_capable(CAP_SYS_ADMIN)) &&
56 	    ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
57 	      uid_eq(uid, cred->suid)) || nsown_capable(CAP_SETUID)) &&
58 	    ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
59 	      gid_eq(gid, cred->sgid)) || nsown_capable(CAP_SETGID))) {
60 	       return 0;
61 	}
62 	return -EPERM;
63 }
64 
65 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
66 {
67 	int *fdp = (int*)CMSG_DATA(cmsg);
68 	struct scm_fp_list *fpl = *fplp;
69 	struct file **fpp;
70 	int i, num;
71 
72 	num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
73 
74 	if (num <= 0)
75 		return 0;
76 
77 	if (num > SCM_MAX_FD)
78 		return -EINVAL;
79 
80 	if (!fpl)
81 	{
82 		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
83 		if (!fpl)
84 			return -ENOMEM;
85 		*fplp = fpl;
86 		fpl->count = 0;
87 		fpl->max = SCM_MAX_FD;
88 	}
89 	fpp = &fpl->fp[fpl->count];
90 
91 	if (fpl->count + num > fpl->max)
92 		return -EINVAL;
93 
94 	/*
95 	 *	Verify the descriptors and increment the usage count.
96 	 */
97 
98 	for (i=0; i< num; i++)
99 	{
100 		int fd = fdp[i];
101 		struct file *file;
102 
103 		if (fd < 0 || !(file = fget_raw(fd)))
104 			return -EBADF;
105 		*fpp++ = file;
106 		fpl->count++;
107 	}
108 	return num;
109 }
110 
111 void __scm_destroy(struct scm_cookie *scm)
112 {
113 	struct scm_fp_list *fpl = scm->fp;
114 	int i;
115 
116 	if (fpl) {
117 		scm->fp = NULL;
118 		for (i=fpl->count-1; i>=0; i--)
119 			fput(fpl->fp[i]);
120 		kfree(fpl);
121 	}
122 }
123 EXPORT_SYMBOL(__scm_destroy);
124 
125 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
126 {
127 	struct cmsghdr *cmsg;
128 	int err;
129 
130 	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
131 	{
132 		err = -EINVAL;
133 
134 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
135 		/* The first check was omitted in <= 2.2.5. The reasoning was
136 		   that parser checks cmsg_len in any case, so that
137 		   additional check would be work duplication.
138 		   But if cmsg_level is not SOL_SOCKET, we do not check
139 		   for too short ancillary data object at all! Oops.
140 		   OK, let's add it...
141 		 */
142 		if (!CMSG_OK(msg, cmsg))
143 			goto error;
144 
145 		if (cmsg->cmsg_level != SOL_SOCKET)
146 			continue;
147 
148 		switch (cmsg->cmsg_type)
149 		{
150 		case SCM_RIGHTS:
151 			if (!sock->ops || sock->ops->family != PF_UNIX)
152 				goto error;
153 			err=scm_fp_copy(cmsg, &p->fp);
154 			if (err<0)
155 				goto error;
156 			break;
157 		case SCM_CREDENTIALS:
158 		{
159 			struct ucred creds;
160 			kuid_t uid;
161 			kgid_t gid;
162 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
163 				goto error;
164 			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
165 			err = scm_check_creds(&creds);
166 			if (err)
167 				goto error;
168 
169 			p->creds.pid = creds.pid;
170 			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
171 				struct pid *pid;
172 				err = -ESRCH;
173 				pid = find_get_pid(creds.pid);
174 				if (!pid)
175 					goto error;
176 				put_pid(p->pid);
177 				p->pid = pid;
178 			}
179 
180 			err = -EINVAL;
181 			uid = make_kuid(current_user_ns(), creds.uid);
182 			gid = make_kgid(current_user_ns(), creds.gid);
183 			if (!uid_valid(uid) || !gid_valid(gid))
184 				goto error;
185 
186 			p->creds.uid = uid;
187 			p->creds.gid = gid;
188 
189 			if (!p->cred ||
190 			    !uid_eq(p->cred->euid, uid) ||
191 			    !gid_eq(p->cred->egid, gid)) {
192 				struct cred *cred;
193 				err = -ENOMEM;
194 				cred = prepare_creds();
195 				if (!cred)
196 					goto error;
197 
198 				cred->uid = cred->euid = uid;
199 				cred->gid = cred->egid = gid;
200 				if (p->cred)
201 					put_cred(p->cred);
202 				p->cred = cred;
203 			}
204 			break;
205 		}
206 		default:
207 			goto error;
208 		}
209 	}
210 
211 	if (p->fp && !p->fp->count)
212 	{
213 		kfree(p->fp);
214 		p->fp = NULL;
215 	}
216 	return 0;
217 
218 error:
219 	scm_destroy(p);
220 	return err;
221 }
222 EXPORT_SYMBOL(__scm_send);
223 
224 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
225 {
226 	struct cmsghdr __user *cm
227 		= (__force struct cmsghdr __user *)msg->msg_control;
228 	struct cmsghdr cmhdr;
229 	int cmlen = CMSG_LEN(len);
230 	int err;
231 
232 	if (MSG_CMSG_COMPAT & msg->msg_flags)
233 		return put_cmsg_compat(msg, level, type, len, data);
234 
235 	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
236 		msg->msg_flags |= MSG_CTRUNC;
237 		return 0; /* XXX: return error? check spec. */
238 	}
239 	if (msg->msg_controllen < cmlen) {
240 		msg->msg_flags |= MSG_CTRUNC;
241 		cmlen = msg->msg_controllen;
242 	}
243 	cmhdr.cmsg_level = level;
244 	cmhdr.cmsg_type = type;
245 	cmhdr.cmsg_len = cmlen;
246 
247 	err = -EFAULT;
248 	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
249 		goto out;
250 	if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
251 		goto out;
252 	cmlen = CMSG_SPACE(len);
253 	if (msg->msg_controllen < cmlen)
254 		cmlen = msg->msg_controllen;
255 	msg->msg_control += cmlen;
256 	msg->msg_controllen -= cmlen;
257 	err = 0;
258 out:
259 	return err;
260 }
261 EXPORT_SYMBOL(put_cmsg);
262 
263 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
264 {
265 	struct cmsghdr __user *cm
266 		= (__force struct cmsghdr __user*)msg->msg_control;
267 
268 	int fdmax = 0;
269 	int fdnum = scm->fp->count;
270 	struct file **fp = scm->fp->fp;
271 	int __user *cmfptr;
272 	int err = 0, i;
273 
274 	if (MSG_CMSG_COMPAT & msg->msg_flags) {
275 		scm_detach_fds_compat(msg, scm);
276 		return;
277 	}
278 
279 	if (msg->msg_controllen > sizeof(struct cmsghdr))
280 		fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
281 			 / sizeof(int));
282 
283 	if (fdnum < fdmax)
284 		fdmax = fdnum;
285 
286 	for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
287 	     i++, cmfptr++)
288 	{
289 		struct socket *sock;
290 		int new_fd;
291 		err = security_file_receive(fp[i]);
292 		if (err)
293 			break;
294 		err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
295 					  ? O_CLOEXEC : 0);
296 		if (err < 0)
297 			break;
298 		new_fd = err;
299 		err = put_user(new_fd, cmfptr);
300 		if (err) {
301 			put_unused_fd(new_fd);
302 			break;
303 		}
304 		/* Bump the usage count and install the file. */
305 		sock = sock_from_file(fp[i], &err);
306 		if (sock) {
307 			sock_update_netprioidx(sock->sk, current);
308 			sock_update_classid(sock->sk, current);
309 		}
310 		fd_install(new_fd, get_file(fp[i]));
311 	}
312 
313 	if (i > 0)
314 	{
315 		int cmlen = CMSG_LEN(i*sizeof(int));
316 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
317 		if (!err)
318 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
319 		if (!err)
320 			err = put_user(cmlen, &cm->cmsg_len);
321 		if (!err) {
322 			cmlen = CMSG_SPACE(i*sizeof(int));
323 			msg->msg_control += cmlen;
324 			msg->msg_controllen -= cmlen;
325 		}
326 	}
327 	if (i < fdnum || (fdnum && fdmax <= 0))
328 		msg->msg_flags |= MSG_CTRUNC;
329 
330 	/*
331 	 * All of the files that fit in the message have had their
332 	 * usage counts incremented, so we just free the list.
333 	 */
334 	__scm_destroy(scm);
335 }
336 EXPORT_SYMBOL(scm_detach_fds);
337 
338 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
339 {
340 	struct scm_fp_list *new_fpl;
341 	int i;
342 
343 	if (!fpl)
344 		return NULL;
345 
346 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
347 			  GFP_KERNEL);
348 	if (new_fpl) {
349 		for (i = 0; i < fpl->count; i++)
350 			get_file(fpl->fp[i]);
351 		new_fpl->max = new_fpl->count;
352 	}
353 	return new_fpl;
354 }
355 EXPORT_SYMBOL(scm_fp_dup);
356