1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* scm.c - Socket level control messages processing.
3  *
4  * Author:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
5  *              Alignment and value checking mods by Craig Metz
6  */
7 
8 #include <linux/module.h>
9 #include <linux/signal.h>
10 #include <linux/capability.h>
11 #include <linux/errno.h>
12 #include <linux/sched.h>
13 #include <linux/sched/user.h>
14 #include <linux/mm.h>
15 #include <linux/kernel.h>
16 #include <linux/stat.h>
17 #include <linux/socket.h>
18 #include <linux/file.h>
19 #include <linux/fcntl.h>
20 #include <linux/net.h>
21 #include <linux/interrupt.h>
22 #include <linux/netdevice.h>
23 #include <linux/security.h>
24 #include <linux/pid_namespace.h>
25 #include <linux/pid.h>
26 #include <linux/nsproxy.h>
27 #include <linux/slab.h>
28 #include <linux/errqueue.h>
29 
30 #include <linux/uaccess.h>
31 
32 #include <net/protocol.h>
33 #include <linux/skbuff.h>
34 #include <net/sock.h>
35 #include <net/compat.h>
36 #include <net/scm.h>
37 #include <net/cls_cgroup.h>
38 
39 
40 /*
41  *	Only allow a user to send credentials, that they could set with
42  *	setu(g)id.
43  */
44 
scm_check_creds(struct ucred * creds)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) ||
55 	     ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
56 	    ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
57 	      uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
58 	    ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
59 	      gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
60 	       return 0;
61 	}
62 	return -EPERM;
63 }
64 
scm_fp_copy(struct cmsghdr * cmsg,struct scm_fp_list ** fplp)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 - 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_ACCOUNT);
83 		if (!fpl)
84 			return -ENOMEM;
85 		*fplp = fpl;
86 		fpl->count = 0;
87 		fpl->max = SCM_MAX_FD;
88 		fpl->user = NULL;
89 	}
90 	fpp = &fpl->fp[fpl->count];
91 
92 	if (fpl->count + num > fpl->max)
93 		return -EINVAL;
94 
95 	/*
96 	 *	Verify the descriptors and increment the usage count.
97 	 */
98 
99 	for (i=0; i< num; i++)
100 	{
101 		int fd = fdp[i];
102 		struct file *file;
103 
104 		if (fd < 0 || !(file = fget_raw(fd)))
105 			return -EBADF;
106 		*fpp++ = file;
107 		fpl->count++;
108 	}
109 
110 	if (!fpl->user)
111 		fpl->user = get_uid(current_user());
112 
113 	return num;
114 }
115 
__scm_destroy(struct scm_cookie * scm)116 void __scm_destroy(struct scm_cookie *scm)
117 {
118 	struct scm_fp_list *fpl = scm->fp;
119 	int i;
120 
121 	if (fpl) {
122 		scm->fp = NULL;
123 		for (i=fpl->count-1; i>=0; i--)
124 			fput(fpl->fp[i]);
125 		free_uid(fpl->user);
126 		kfree(fpl);
127 	}
128 }
129 EXPORT_SYMBOL(__scm_destroy);
130 
__scm_send(struct socket * sock,struct msghdr * msg,struct scm_cookie * p)131 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
132 {
133 	struct cmsghdr *cmsg;
134 	int err;
135 
136 	for_each_cmsghdr(cmsg, msg) {
137 		err = -EINVAL;
138 
139 		/* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
140 		/* The first check was omitted in <= 2.2.5. The reasoning was
141 		   that parser checks cmsg_len in any case, so that
142 		   additional check would be work duplication.
143 		   But if cmsg_level is not SOL_SOCKET, we do not check
144 		   for too short ancillary data object at all! Oops.
145 		   OK, let's add it...
146 		 */
147 		if (!CMSG_OK(msg, cmsg))
148 			goto error;
149 
150 		if (cmsg->cmsg_level != SOL_SOCKET)
151 			continue;
152 
153 		switch (cmsg->cmsg_type)
154 		{
155 		case SCM_RIGHTS:
156 			if (!sock->ops || sock->ops->family != PF_UNIX)
157 				goto error;
158 			err=scm_fp_copy(cmsg, &p->fp);
159 			if (err<0)
160 				goto error;
161 			break;
162 		case SCM_CREDENTIALS:
163 		{
164 			struct ucred creds;
165 			kuid_t uid;
166 			kgid_t gid;
167 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
168 				goto error;
169 			memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
170 			err = scm_check_creds(&creds);
171 			if (err)
172 				goto error;
173 
174 			p->creds.pid = creds.pid;
175 			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
176 				struct pid *pid;
177 				err = -ESRCH;
178 				pid = find_get_pid(creds.pid);
179 				if (!pid)
180 					goto error;
181 				put_pid(p->pid);
182 				p->pid = pid;
183 			}
184 
185 			err = -EINVAL;
186 			uid = make_kuid(current_user_ns(), creds.uid);
187 			gid = make_kgid(current_user_ns(), creds.gid);
188 			if (!uid_valid(uid) || !gid_valid(gid))
189 				goto error;
190 
191 			p->creds.uid = uid;
192 			p->creds.gid = gid;
193 			break;
194 		}
195 		default:
196 			goto error;
197 		}
198 	}
199 
200 	if (p->fp && !p->fp->count)
201 	{
202 		kfree(p->fp);
203 		p->fp = NULL;
204 	}
205 	return 0;
206 
207 error:
208 	scm_destroy(p);
209 	return err;
210 }
211 EXPORT_SYMBOL(__scm_send);
212 
put_cmsg(struct msghdr * msg,int level,int type,int len,void * data)213 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
214 {
215 	int cmlen = CMSG_LEN(len);
216 
217 	if (msg->msg_flags & MSG_CMSG_COMPAT)
218 		return put_cmsg_compat(msg, level, type, len, data);
219 
220 	if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
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 
229 	if (msg->msg_control_is_user) {
230 		struct cmsghdr __user *cm = msg->msg_control_user;
231 
232 		if (!user_write_access_begin(cm, cmlen))
233 			goto efault;
234 
235 		unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
236 		unsafe_put_user(level, &cm->cmsg_level, efault_end);
237 		unsafe_put_user(type, &cm->cmsg_type, efault_end);
238 		unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
239 				    cmlen - sizeof(*cm), efault_end);
240 		user_write_access_end();
241 	} else {
242 		struct cmsghdr *cm = msg->msg_control;
243 
244 		cm->cmsg_level = level;
245 		cm->cmsg_type = type;
246 		cm->cmsg_len = cmlen;
247 		memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
248 	}
249 
250 	cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
251 	msg->msg_control += cmlen;
252 	msg->msg_controllen -= cmlen;
253 	return 0;
254 
255 efault_end:
256 	user_write_access_end();
257 efault:
258 	return -EFAULT;
259 }
260 EXPORT_SYMBOL(put_cmsg);
261 
put_cmsg_scm_timestamping64(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)262 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
263 {
264 	struct scm_timestamping64 tss;
265 	int i;
266 
267 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
268 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
269 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
270 	}
271 
272 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
273 }
274 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
275 
put_cmsg_scm_timestamping(struct msghdr * msg,struct scm_timestamping_internal * tss_internal)276 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
277 {
278 	struct scm_timestamping tss;
279 	int i;
280 
281 	for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
282 		tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
283 		tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
284 	}
285 
286 	put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
287 }
288 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
289 
scm_max_fds(struct msghdr * msg)290 static int scm_max_fds(struct msghdr *msg)
291 {
292 	if (msg->msg_controllen <= sizeof(struct cmsghdr))
293 		return 0;
294 	return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
295 }
296 
scm_detach_fds(struct msghdr * msg,struct scm_cookie * scm)297 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
298 {
299 	struct cmsghdr __user *cm =
300 		(__force struct cmsghdr __user *)msg->msg_control;
301 	unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
302 	int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
303 	int __user *cmsg_data = CMSG_USER_DATA(cm);
304 	int err = 0, i;
305 
306 	/* no use for FD passing from kernel space callers */
307 	if (WARN_ON_ONCE(!msg->msg_control_is_user))
308 		return;
309 
310 	if (msg->msg_flags & MSG_CMSG_COMPAT) {
311 		scm_detach_fds_compat(msg, scm);
312 		return;
313 	}
314 
315 	for (i = 0; i < fdmax; i++) {
316 		err = receive_fd_user(scm->fp->fp[i], cmsg_data + i, o_flags);
317 		if (err < 0)
318 			break;
319 	}
320 
321 	if (i > 0) {
322 		int cmlen = CMSG_LEN(i * sizeof(int));
323 
324 		err = put_user(SOL_SOCKET, &cm->cmsg_level);
325 		if (!err)
326 			err = put_user(SCM_RIGHTS, &cm->cmsg_type);
327 		if (!err)
328 			err = put_user(cmlen, &cm->cmsg_len);
329 		if (!err) {
330 			cmlen = CMSG_SPACE(i * sizeof(int));
331 			if (msg->msg_controllen < cmlen)
332 				cmlen = msg->msg_controllen;
333 			msg->msg_control += cmlen;
334 			msg->msg_controllen -= cmlen;
335 		}
336 	}
337 
338 	if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
339 		msg->msg_flags |= MSG_CTRUNC;
340 
341 	/*
342 	 * All of the files that fit in the message have had their usage counts
343 	 * incremented, so we just free the list.
344 	 */
345 	__scm_destroy(scm);
346 }
347 EXPORT_SYMBOL(scm_detach_fds);
348 
scm_fp_dup(struct scm_fp_list * fpl)349 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
350 {
351 	struct scm_fp_list *new_fpl;
352 	int i;
353 
354 	if (!fpl)
355 		return NULL;
356 
357 	new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
358 			  GFP_KERNEL_ACCOUNT);
359 	if (new_fpl) {
360 		for (i = 0; i < fpl->count; i++)
361 			get_file(fpl->fp[i]);
362 		new_fpl->max = new_fpl->count;
363 		new_fpl->user = get_uid(fpl->user);
364 	}
365 	return new_fpl;
366 }
367 EXPORT_SYMBOL(scm_fp_dup);
368