xref: /openbmc/linux/net/core/scm.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
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 
30 #include <asm/system.h>
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 
49 	if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
50 	    ((creds->uid == cred->uid   || creds->uid == cred->euid ||
51 	      creds->uid == cred->suid) || capable(CAP_SETUID)) &&
52 	    ((creds->gid == cred->gid   || creds->gid == cred->egid ||
53 	      creds->gid == cred->sgid) || capable(CAP_SETGID))) {
54 	       return 0;
55 	}
56 	return -EPERM;
57 }
58 
59 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
60 {
61 	int *fdp = (int*)CMSG_DATA(cmsg);
62 	struct scm_fp_list *fpl = *fplp;
63 	struct file **fpp;
64 	int i, num;
65 
66 	num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
67 
68 	if (num <= 0)
69 		return 0;
70 
71 	if (num > SCM_MAX_FD)
72 		return -EINVAL;
73 
74 	if (!fpl)
75 	{
76 		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
77 		if (!fpl)
78 			return -ENOMEM;
79 		*fplp = fpl;
80 		fpl->count = 0;
81 	}
82 	fpp = &fpl->fp[fpl->count];
83 
84 	if (fpl->count + num > SCM_MAX_FD)
85 		return -EINVAL;
86 
87 	/*
88 	 *	Verify the descriptors and increment the usage count.
89 	 */
90 
91 	for (i=0; i< num; i++)
92 	{
93 		int fd = fdp[i];
94 		struct file *file;
95 
96 		if (fd < 0 || !(file = fget(fd)))
97 			return -EBADF;
98 		*fpp++ = file;
99 		fpl->count++;
100 	}
101 	return num;
102 }
103 
104 void __scm_destroy(struct scm_cookie *scm)
105 {
106 	struct scm_fp_list *fpl = scm->fp;
107 	int i;
108 
109 	if (fpl) {
110 		scm->fp = NULL;
111 		if (current->scm_work_list) {
112 			list_add_tail(&fpl->list, current->scm_work_list);
113 		} else {
114 			LIST_HEAD(work_list);
115 
116 			current->scm_work_list = &work_list;
117 
118 			list_add(&fpl->list, &work_list);
119 			while (!list_empty(&work_list)) {
120 				fpl = list_first_entry(&work_list, struct scm_fp_list, list);
121 
122 				list_del(&fpl->list);
123 				for (i=fpl->count-1; i>=0; i--)
124 					fput(fpl->fp[i]);
125 				kfree(fpl);
126 			}
127 
128 			current->scm_work_list = NULL;
129 		}
130 	}
131 }
132 
133 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
134 {
135 	struct cmsghdr *cmsg;
136 	int err;
137 
138 	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
139 	{
140 		err = -EINVAL;
141 
142 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
143 		/* The first check was omitted in <= 2.2.5. The reasoning was
144 		   that parser checks cmsg_len in any case, so that
145 		   additional check would be work duplication.
146 		   But if cmsg_level is not SOL_SOCKET, we do not check
147 		   for too short ancillary data object at all! Oops.
148 		   OK, let's add it...
149 		 */
150 		if (!CMSG_OK(msg, cmsg))
151 			goto error;
152 
153 		if (cmsg->cmsg_level != SOL_SOCKET)
154 			continue;
155 
156 		switch (cmsg->cmsg_type)
157 		{
158 		case SCM_RIGHTS:
159 			err=scm_fp_copy(cmsg, &p->fp);
160 			if (err<0)
161 				goto error;
162 			break;
163 		case SCM_CREDENTIALS:
164 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
165 				goto error;
166 			memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
167 			err = scm_check_creds(&p->creds);
168 			if (err)
169 				goto error;
170 			break;
171 		default:
172 			goto error;
173 		}
174 	}
175 
176 	if (p->fp && !p->fp->count)
177 	{
178 		kfree(p->fp);
179 		p->fp = NULL;
180 	}
181 	return 0;
182 
183 error:
184 	scm_destroy(p);
185 	return err;
186 }
187 
188 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
189 {
190 	struct cmsghdr __user *cm
191 		= (__force struct cmsghdr __user *)msg->msg_control;
192 	struct cmsghdr cmhdr;
193 	int cmlen = CMSG_LEN(len);
194 	int err;
195 
196 	if (MSG_CMSG_COMPAT & msg->msg_flags)
197 		return put_cmsg_compat(msg, level, type, len, data);
198 
199 	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
200 		msg->msg_flags |= MSG_CTRUNC;
201 		return 0; /* XXX: return error? check spec. */
202 	}
203 	if (msg->msg_controllen < cmlen) {
204 		msg->msg_flags |= MSG_CTRUNC;
205 		cmlen = msg->msg_controllen;
206 	}
207 	cmhdr.cmsg_level = level;
208 	cmhdr.cmsg_type = type;
209 	cmhdr.cmsg_len = cmlen;
210 
211 	err = -EFAULT;
212 	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
213 		goto out;
214 	if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
215 		goto out;
216 	cmlen = CMSG_SPACE(len);
217 	if (msg->msg_controllen < cmlen)
218 		cmlen = msg->msg_controllen;
219 	msg->msg_control += cmlen;
220 	msg->msg_controllen -= cmlen;
221 	err = 0;
222 out:
223 	return err;
224 }
225 
226 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
227 {
228 	struct cmsghdr __user *cm
229 		= (__force struct cmsghdr __user*)msg->msg_control;
230 
231 	int fdmax = 0;
232 	int fdnum = scm->fp->count;
233 	struct file **fp = scm->fp->fp;
234 	int __user *cmfptr;
235 	int err = 0, i;
236 
237 	if (MSG_CMSG_COMPAT & msg->msg_flags) {
238 		scm_detach_fds_compat(msg, scm);
239 		return;
240 	}
241 
242 	if (msg->msg_controllen > sizeof(struct cmsghdr))
243 		fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
244 			 / sizeof(int));
245 
246 	if (fdnum < fdmax)
247 		fdmax = fdnum;
248 
249 	for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
250 	     i++, cmfptr++)
251 	{
252 		int new_fd;
253 		err = security_file_receive(fp[i]);
254 		if (err)
255 			break;
256 		err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
257 					  ? O_CLOEXEC : 0);
258 		if (err < 0)
259 			break;
260 		new_fd = err;
261 		err = put_user(new_fd, cmfptr);
262 		if (err) {
263 			put_unused_fd(new_fd);
264 			break;
265 		}
266 		/* Bump the usage count and install the file. */
267 		get_file(fp[i]);
268 		fd_install(new_fd, fp[i]);
269 	}
270 
271 	if (i > 0)
272 	{
273 		int cmlen = CMSG_LEN(i*sizeof(int));
274 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
275 		if (!err)
276 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
277 		if (!err)
278 			err = put_user(cmlen, &cm->cmsg_len);
279 		if (!err) {
280 			cmlen = CMSG_SPACE(i*sizeof(int));
281 			msg->msg_control += cmlen;
282 			msg->msg_controllen -= cmlen;
283 		}
284 	}
285 	if (i < fdnum || (fdnum && fdmax <= 0))
286 		msg->msg_flags |= MSG_CTRUNC;
287 
288 	/*
289 	 * All of the files that fit in the message have had their
290 	 * usage counts incremented, so we just free the list.
291 	 */
292 	__scm_destroy(scm);
293 }
294 
295 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
296 {
297 	struct scm_fp_list *new_fpl;
298 	int i;
299 
300 	if (!fpl)
301 		return NULL;
302 
303 	new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
304 	if (new_fpl) {
305 		for (i=fpl->count-1; i>=0; i--)
306 			get_file(fpl->fp[i]);
307 		memcpy(new_fpl, fpl, sizeof(*fpl));
308 	}
309 	return new_fpl;
310 }
311 
312 EXPORT_SYMBOL(__scm_destroy);
313 EXPORT_SYMBOL(__scm_send);
314 EXPORT_SYMBOL(put_cmsg);
315 EXPORT_SYMBOL(scm_detach_fds);
316 EXPORT_SYMBOL(scm_fp_dup);
317