xref: /openbmc/linux/net/core/scm.c (revision 6a613ac6) 
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_namespace.h>
28 #include <linux/pid.h>
29 #include <linux/nsproxy.h>
30 #include <linux/slab.h>
31 
32 #include <asm/uaccess.h>
33 
34 #include <net/protocol.h>
35 #include <linux/skbuff.h>
36 #include <net/sock.h>
37 #include <net/compat.h>
38 #include <net/scm.h>
39 #include <net/cls_cgroup.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 - CMSG_ALIGN(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);
85 		if (!fpl)
86 			return -ENOMEM;
87 		*fplp = fpl;
88 		fpl->count = 0;
89 		fpl->max = SCM_MAX_FD;
90 	}
91 	fpp = &fpl->fp[fpl->count];
92 
93 	if (fpl->count + num > fpl->max)
94 		return -EINVAL;
95 
96 	/*
97 	 *	Verify the descriptors and increment the usage count.
98 	 */
99 
100 	for (i=0; i< num; i++)
101 	{
102 		int fd = fdp[i];
103 		struct file *file;
104 
105 		if (fd < 0 || !(file = fget_raw(fd)))
106 			return -EBADF;
107 		*fpp++ = file;
108 		fpl->count++;
109 	}
110 	return num;
111 }
112 
113 void __scm_destroy(struct scm_cookie *scm)
114 {
115 	struct scm_fp_list *fpl = scm->fp;
116 	int i;
117 
118 	if (fpl) {
119 		scm->fp = NULL;
120 		for (i=fpl->count-1; i>=0; i--)
121 			fput(fpl->fp[i]);
122 		kfree(fpl);
123 	}
124 }
125 EXPORT_SYMBOL(__scm_destroy);
126 
127 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
128 {
129 	struct cmsghdr *cmsg;
130 	int err;
131 
132 	for_each_cmsghdr(cmsg, msg) {
133 		err = -EINVAL;
134 
135 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
136 		/* The first check was omitted in <= 2.2.5. The reasoning was
137 		   that parser checks cmsg_len in any case, so that
138 		   additional check would be work duplication.
139 		   But if cmsg_level is not SOL_SOCKET, we do not check
140 		   for too short ancillary data object at all! Oops.
141 		   OK, let's add it...
142 		 */
143 		if (!CMSG_OK(msg, cmsg))
144 			goto error;
145 
146 		if (cmsg->cmsg_level != SOL_SOCKET)
147 			continue;
148 
149 		switch (cmsg->cmsg_type)
150 		{
151 		case SCM_RIGHTS:
152 			if (!sock->ops || sock->ops->family != PF_UNIX)
153 				goto error;
154 			err=scm_fp_copy(cmsg, &p->fp);
155 			if (err<0)
156 				goto error;
157 			break;
158 		case SCM_CREDENTIALS:
159 		{
160 			struct ucred creds;
161 			kuid_t uid;
162 			kgid_t gid;
163 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
164 				goto error;
165 			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
166 			err = scm_check_creds(&creds);
167 			if (err)
168 				goto error;
169 
170 			p->creds.pid = creds.pid;
171 			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
172 				struct pid *pid;
173 				err = -ESRCH;
174 				pid = find_get_pid(creds.pid);
175 				if (!pid)
176 					goto error;
177 				put_pid(p->pid);
178 				p->pid = pid;
179 			}
180 
181 			err = -EINVAL;
182 			uid = make_kuid(current_user_ns(), creds.uid);
183 			gid = make_kgid(current_user_ns(), creds.gid);
184 			if (!uid_valid(uid) || !gid_valid(gid))
185 				goto error;
186 
187 			p->creds.uid = uid;
188 			p->creds.gid = gid;
189 			break;
190 		}
191 		default:
192 			goto error;
193 		}
194 	}
195 
196 	if (p->fp && !p->fp->count)
197 	{
198 		kfree(p->fp);
199 		p->fp = NULL;
200 	}
201 	return 0;
202 
203 error:
204 	scm_destroy(p);
205 	return err;
206 }
207 EXPORT_SYMBOL(__scm_send);
208 
209 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
210 {
211 	struct cmsghdr __user *cm
212 		= (__force struct cmsghdr __user *)msg->msg_control;
213 	struct cmsghdr cmhdr;
214 	int cmlen = CMSG_LEN(len);
215 	int err;
216 
217 	if (MSG_CMSG_COMPAT & msg->msg_flags)
218 		return put_cmsg_compat(msg, level, type, len, data);
219 
220 	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
221 		msg->msg_flags |= MSG_CTRUNC;
222 		return 0; /* XXX: return error? check spec. */
223 	}
224 	if (msg->msg_controllen < cmlen) {
225 		msg->msg_flags |= MSG_CTRUNC;
226 		cmlen = msg->msg_controllen;
227 	}
228 	cmhdr.cmsg_level = level;
229 	cmhdr.cmsg_type = type;
230 	cmhdr.cmsg_len = cmlen;
231 
232 	err = -EFAULT;
233 	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
234 		goto out;
235 	if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
236 		goto out;
237 	cmlen = CMSG_SPACE(len);
238 	if (msg->msg_controllen < cmlen)
239 		cmlen = msg->msg_controllen;
240 	msg->msg_control += cmlen;
241 	msg->msg_controllen -= cmlen;
242 	err = 0;
243 out:
244 	return err;
245 }
246 EXPORT_SYMBOL(put_cmsg);
247 
248 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
249 {
250 	struct cmsghdr __user *cm
251 		= (__force struct cmsghdr __user*)msg->msg_control;
252 
253 	int fdmax = 0;
254 	int fdnum = scm->fp->count;
255 	struct file **fp = scm->fp->fp;
256 	int __user *cmfptr;
257 	int err = 0, i;
258 
259 	if (MSG_CMSG_COMPAT & msg->msg_flags) {
260 		scm_detach_fds_compat(msg, scm);
261 		return;
262 	}
263 
264 	if (msg->msg_controllen > sizeof(struct cmsghdr))
265 		fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
266 			 / sizeof(int));
267 
268 	if (fdnum < fdmax)
269 		fdmax = fdnum;
270 
271 	for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
272 	     i++, cmfptr++)
273 	{
274 		struct socket *sock;
275 		int new_fd;
276 		err = security_file_receive(fp[i]);
277 		if (err)
278 			break;
279 		err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
280 					  ? O_CLOEXEC : 0);
281 		if (err < 0)
282 			break;
283 		new_fd = err;
284 		err = put_user(new_fd, cmfptr);
285 		if (err) {
286 			put_unused_fd(new_fd);
287 			break;
288 		}
289 		/* Bump the usage count and install the file. */
290 		sock = sock_from_file(fp[i], &err);
291 		if (sock) {
292 			sock_update_netprioidx(sock->sk);
293 			sock_update_classid(sock->sk);
294 		}
295 		fd_install(new_fd, get_file(fp[i]));
296 	}
297 
298 	if (i > 0)
299 	{
300 		int cmlen = CMSG_LEN(i*sizeof(int));
301 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
302 		if (!err)
303 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
304 		if (!err)
305 			err = put_user(cmlen, &cm->cmsg_len);
306 		if (!err) {
307 			cmlen = CMSG_SPACE(i*sizeof(int));
308 			if (msg->msg_controllen < cmlen)
309 				cmlen = msg->msg_controllen;
310 			msg->msg_control += cmlen;
311 			msg->msg_controllen -= cmlen;
312 		}
313 	}
314 	if (i < fdnum || (fdnum && fdmax <= 0))
315 		msg->msg_flags |= MSG_CTRUNC;
316 
317 	/*
318 	 * All of the files that fit in the message have had their
319 	 * usage counts incremented, so we just free the list.
320 	 */
321 	__scm_destroy(scm);
322 }
323 EXPORT_SYMBOL(scm_detach_fds);
324 
325 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
326 {
327 	struct scm_fp_list *new_fpl;
328 	int i;
329 
330 	if (!fpl)
331 		return NULL;
332 
333 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
334 			  GFP_KERNEL);
335 	if (new_fpl) {
336 		for (i = 0; i < fpl->count; i++)
337 			get_file(fpl->fp[i]);
338 		new_fpl->max = new_fpl->count;
339 	}
340 	return new_fpl;
341 }
342 EXPORT_SYMBOL(scm_fp_dup);
343