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
28#include <asm/system.h>
29#include <asm/uaccess.h>
30
31#include <net/protocol.h>
32#include <linux/skbuff.h>
33#include <net/sock.h>
34#include <net/compat.h>
35#include <net/scm.h>
36
37
38/*
39 *	Only allow a user to send credentials, that they could set with
40 *	setu(g)id.
41 */
42
43static __inline__ int scm_check_creds(struct ucred *creds)
44{
45	if ((creds->pid == current->tgid || capable(CAP_SYS_ADMIN)) &&
46	    ((creds->uid == current->uid || creds->uid == current->euid ||
47	      creds->uid == current->suid) || capable(CAP_SETUID)) &&
48	    ((creds->gid == current->gid || creds->gid == current->egid ||
49	      creds->gid == current->sgid) || capable(CAP_SETGID))) {
50	       return 0;
51	}
52	return -EPERM;
53}
54
55static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
56{
57	int *fdp = (int*)CMSG_DATA(cmsg);
58	struct scm_fp_list *fpl = *fplp;
59	struct file **fpp;
60	int i, num;
61
62	num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
63
64	if (num <= 0)
65		return 0;
66
67	if (num > SCM_MAX_FD)
68		return -EINVAL;
69
70	if (!fpl)
71	{
72		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
73		if (!fpl)
74			return -ENOMEM;
75		*fplp = fpl;
76		fpl->count = 0;
77	}
78	fpp = &fpl->fp[fpl->count];
79
80	if (fpl->count + num > SCM_MAX_FD)
81		return -EINVAL;
82
83	/*
84	 *	Verify the descriptors and increment the usage count.
85	 */
86
87	for (i=0; i< num; i++)
88	{
89		int fd = fdp[i];
90		struct file *file;
91
92		if (fd < 0 || !(file = fget(fd)))
93			return -EBADF;
94		*fpp++ = file;
95		fpl->count++;
96	}
97	return num;
98}
99
100void __scm_destroy(struct scm_cookie *scm)
101{
102	struct scm_fp_list *fpl = scm->fp;
103	int i;
104
105	if (fpl) {
106		scm->fp = NULL;
107		for (i=fpl->count-1; i>=0; i--)
108			fput(fpl->fp[i]);
109		kfree(fpl);
110	}
111}
112
113int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
114{
115	struct cmsghdr *cmsg;
116	int err;
117
118	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
119	{
120		err = -EINVAL;
121
122		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
123		/* The first check was omitted in <= 2.2.5. The reasoning was
124		   that parser checks cmsg_len in any case, so that
125		   additional check would be work duplication.
126		   But if cmsg_level is not SOL_SOCKET, we do not check
127		   for too short ancillary data object at all! Oops.
128		   OK, let's add it...
129		 */
130		if (!CMSG_OK(msg, cmsg))
131			goto error;
132
133		if (cmsg->cmsg_level != SOL_SOCKET)
134			continue;
135
136		switch (cmsg->cmsg_type)
137		{
138		case SCM_RIGHTS:
139			err=scm_fp_copy(cmsg, &p->fp);
140			if (err<0)
141				goto error;
142			break;
143		case SCM_CREDENTIALS:
144			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
145				goto error;
146			memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
147			err = scm_check_creds(&p->creds);
148			if (err)
149				goto error;
150			break;
151		default:
152			goto error;
153		}
154	}
155
156	if (p->fp && !p->fp->count)
157	{
158		kfree(p->fp);
159		p->fp = NULL;
160	}
161	return 0;
162
163error:
164	scm_destroy(p);
165	return err;
166}
167
168int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
169{
170	struct cmsghdr __user *cm = (struct cmsghdr __user *)msg->msg_control;
171	struct cmsghdr cmhdr;
172	int cmlen = CMSG_LEN(len);
173	int err;
174
175	if (MSG_CMSG_COMPAT & msg->msg_flags)
176		return put_cmsg_compat(msg, level, type, len, data);
177
178	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
179		msg->msg_flags |= MSG_CTRUNC;
180		return 0;
181	}
182	if (msg->msg_controllen < cmlen) {
183		msg->msg_flags |= MSG_CTRUNC;
184		cmlen = msg->msg_controllen;
185	}
186	cmhdr.cmsg_level = level;
187	cmhdr.cmsg_type = type;
188	cmhdr.cmsg_len = cmlen;
189
190	err = -EFAULT;
191	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
192		goto out;
193	if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
194		goto out;
195	cmlen = CMSG_SPACE(len);
196	msg->msg_control += cmlen;
197	msg->msg_controllen -= cmlen;
198	err = 0;
199out:
200	return err;
201}
202
203void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
204{
205	struct cmsghdr __user *cm = (struct cmsghdr __user*)msg->msg_control;
206
207	int fdmax = 0;
208	int fdnum = scm->fp->count;
209	struct file **fp = scm->fp->fp;
210	int __user *cmfptr;
211	int err = 0, i;
212
213	if (MSG_CMSG_COMPAT & msg->msg_flags) {
214		scm_detach_fds_compat(msg, scm);
215		return;
216	}
217
218	if (msg->msg_controllen > sizeof(struct cmsghdr))
219		fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
220			 / sizeof(int));
221
222	if (fdnum < fdmax)
223		fdmax = fdnum;
224
225	for (i=0, cmfptr=(int __user *)CMSG_DATA(cm); i<fdmax; i++, cmfptr++)
226	{
227		int new_fd;
228		err = security_file_receive(fp[i]);
229		if (err)
230			break;
231		err = get_unused_fd();
232		if (err < 0)
233			break;
234		new_fd = err;
235		err = put_user(new_fd, cmfptr);
236		if (err) {
237			put_unused_fd(new_fd);
238			break;
239		}
240		/* Bump the usage count and install the file. */
241		get_file(fp[i]);
242		fd_install(new_fd, fp[i]);
243	}
244
245	if (i > 0)
246	{
247		int cmlen = CMSG_LEN(i*sizeof(int));
248		err = put_user(SOL_SOCKET, &cm->cmsg_level);
249		if (!err)
250			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
251		if (!err)
252			err = put_user(cmlen, &cm->cmsg_len);
253		if (!err) {
254			cmlen = CMSG_SPACE(i*sizeof(int));
255			msg->msg_control += cmlen;
256			msg->msg_controllen -= cmlen;
257		}
258	}
259	if (i < fdnum || (fdnum && fdmax <= 0))
260		msg->msg_flags |= MSG_CTRUNC;
261
262	/*
263	 * All of the files that fit in the message have had their
264	 * usage counts incremented, so we just free the list.
265	 */
266	__scm_destroy(scm);
267}
268
269struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
270{
271	struct scm_fp_list *new_fpl;
272	int i;
273
274	if (!fpl)
275		return NULL;
276
277	new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
278	if (new_fpl) {
279		for (i=fpl->count-1; i>=0; i--)
280			get_file(fpl->fp[i]);
281		memcpy(new_fpl, fpl, sizeof(*fpl));
282	}
283	return new_fpl;
284}
285
286EXPORT_SYMBOL(__scm_destroy);
287EXPORT_SYMBOL(__scm_send);
288EXPORT_SYMBOL(put_cmsg);
289EXPORT_SYMBOL(scm_detach_fds);
290EXPORT_SYMBOL(scm_fp_dup);
291