scm: lower SCM_MAX_FD
[linux-2.6.git] / net / core / scm.c
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/system.h>
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
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
50         if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
51             ((creds->uid == cred->uid   || creds->uid == cred->euid ||
52               creds->uid == cred->suid) || capable(CAP_SETUID)) &&
53             ((creds->gid == cred->gid   || creds->gid == cred->egid ||
54               creds->gid == cred->sgid) || capable(CAP_SETGID))) {
55                return 0;
56         }
57         return -EPERM;
58 }
59
60 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
61 {
62         int *fdp = (int*)CMSG_DATA(cmsg);
63         struct scm_fp_list *fpl = *fplp;
64         struct file **fpp;
65         int i, num;
66
67         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
68
69         if (num <= 0)
70                 return 0;
71
72         if (num > SCM_MAX_FD)
73                 return -EINVAL;
74
75         if (!fpl)
76         {
77                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
78                 if (!fpl)
79                         return -ENOMEM;
80                 *fplp = fpl;
81                 fpl->count = 0;
82                 fpl->max = SCM_MAX_FD;
83         }
84         fpp = &fpl->fp[fpl->count];
85
86         if (fpl->count + num > fpl->max)
87                 return -EINVAL;
88
89         /*
90          *      Verify the descriptors and increment the usage count.
91          */
92
93         for (i=0; i< num; i++)
94         {
95                 int fd = fdp[i];
96                 struct file *file;
97
98                 if (fd < 0 || !(file = fget(fd)))
99                         return -EBADF;
100                 *fpp++ = file;
101                 fpl->count++;
102         }
103         return num;
104 }
105
106 void __scm_destroy(struct scm_cookie *scm)
107 {
108         struct scm_fp_list *fpl = scm->fp;
109         int i;
110
111         if (fpl) {
112                 scm->fp = NULL;
113                 if (current->scm_work_list) {
114                         list_add_tail(&fpl->list, current->scm_work_list);
115                 } else {
116                         LIST_HEAD(work_list);
117
118                         current->scm_work_list = &work_list;
119
120                         list_add(&fpl->list, &work_list);
121                         while (!list_empty(&work_list)) {
122                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
123
124                                 list_del(&fpl->list);
125                                 for (i=fpl->count-1; i>=0; i--)
126                                         fput(fpl->fp[i]);
127                                 kfree(fpl);
128                         }
129
130                         current->scm_work_list = NULL;
131                 }
132         }
133 }
134 EXPORT_SYMBOL(__scm_destroy);
135
136 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
137 {
138         struct cmsghdr *cmsg;
139         int err;
140
141         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
142         {
143                 err = -EINVAL;
144
145                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
146                 /* The first check was omitted in <= 2.2.5. The reasoning was
147                    that parser checks cmsg_len in any case, so that
148                    additional check would be work duplication.
149                    But if cmsg_level is not SOL_SOCKET, we do not check
150                    for too short ancillary data object at all! Oops.
151                    OK, let's add it...
152                  */
153                 if (!CMSG_OK(msg, cmsg))
154                         goto error;
155
156                 if (cmsg->cmsg_level != SOL_SOCKET)
157                         continue;
158
159                 switch (cmsg->cmsg_type)
160                 {
161                 case SCM_RIGHTS:
162                         if (!sock->ops || sock->ops->family != PF_UNIX)
163                                 goto error;
164                         err=scm_fp_copy(cmsg, &p->fp);
165                         if (err<0)
166                                 goto error;
167                         break;
168                 case SCM_CREDENTIALS:
169                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
170                                 goto error;
171                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
172                         err = scm_check_creds(&p->creds);
173                         if (err)
174                                 goto error;
175
176                         if (pid_vnr(p->pid) != p->creds.pid) {
177                                 struct pid *pid;
178                                 err = -ESRCH;
179                                 pid = find_get_pid(p->creds.pid);
180                                 if (!pid)
181                                         goto error;
182                                 put_pid(p->pid);
183                                 p->pid = pid;
184                         }
185
186                         if ((p->cred->euid != p->creds.uid) ||
187                                 (p->cred->egid != p->creds.gid)) {
188                                 struct cred *cred;
189                                 err = -ENOMEM;
190                                 cred = prepare_creds();
191                                 if (!cred)
192                                         goto error;
193
194                                 cred->uid = cred->euid = p->creds.uid;
195                                 cred->gid = cred->egid = p->creds.uid;
196                                 put_cred(p->cred);
197                                 p->cred = cred;
198                         }
199                         break;
200                 default:
201                         goto error;
202                 }
203         }
204
205         if (p->fp && !p->fp->count)
206         {
207                 kfree(p->fp);
208                 p->fp = NULL;
209         }
210         return 0;
211
212 error:
213         scm_destroy(p);
214         return err;
215 }
216 EXPORT_SYMBOL(__scm_send);
217
218 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
219 {
220         struct cmsghdr __user *cm
221                 = (__force struct cmsghdr __user *)msg->msg_control;
222         struct cmsghdr cmhdr;
223         int cmlen = CMSG_LEN(len);
224         int err;
225
226         if (MSG_CMSG_COMPAT & msg->msg_flags)
227                 return put_cmsg_compat(msg, level, type, len, data);
228
229         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
230                 msg->msg_flags |= MSG_CTRUNC;
231                 return 0; /* XXX: return error? check spec. */
232         }
233         if (msg->msg_controllen < cmlen) {
234                 msg->msg_flags |= MSG_CTRUNC;
235                 cmlen = msg->msg_controllen;
236         }
237         cmhdr.cmsg_level = level;
238         cmhdr.cmsg_type = type;
239         cmhdr.cmsg_len = cmlen;
240
241         err = -EFAULT;
242         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
243                 goto out;
244         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
245                 goto out;
246         cmlen = CMSG_SPACE(len);
247         if (msg->msg_controllen < cmlen)
248                 cmlen = msg->msg_controllen;
249         msg->msg_control += cmlen;
250         msg->msg_controllen -= cmlen;
251         err = 0;
252 out:
253         return err;
254 }
255 EXPORT_SYMBOL(put_cmsg);
256
257 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
258 {
259         struct cmsghdr __user *cm
260                 = (__force struct cmsghdr __user*)msg->msg_control;
261
262         int fdmax = 0;
263         int fdnum = scm->fp->count;
264         struct file **fp = scm->fp->fp;
265         int __user *cmfptr;
266         int err = 0, i;
267
268         if (MSG_CMSG_COMPAT & msg->msg_flags) {
269                 scm_detach_fds_compat(msg, scm);
270                 return;
271         }
272
273         if (msg->msg_controllen > sizeof(struct cmsghdr))
274                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
275                          / sizeof(int));
276
277         if (fdnum < fdmax)
278                 fdmax = fdnum;
279
280         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
281              i++, cmfptr++)
282         {
283                 int new_fd;
284                 err = security_file_receive(fp[i]);
285                 if (err)
286                         break;
287                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
288                                           ? O_CLOEXEC : 0);
289                 if (err < 0)
290                         break;
291                 new_fd = err;
292                 err = put_user(new_fd, cmfptr);
293                 if (err) {
294                         put_unused_fd(new_fd);
295                         break;
296                 }
297                 /* Bump the usage count and install the file. */
298                 get_file(fp[i]);
299                 fd_install(new_fd, fp[i]);
300         }
301
302         if (i > 0)
303         {
304                 int cmlen = CMSG_LEN(i*sizeof(int));
305                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
306                 if (!err)
307                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
308                 if (!err)
309                         err = put_user(cmlen, &cm->cmsg_len);
310                 if (!err) {
311                         cmlen = CMSG_SPACE(i*sizeof(int));
312                         msg->msg_control += cmlen;
313                         msg->msg_controllen -= cmlen;
314                 }
315         }
316         if (i < fdnum || (fdnum && fdmax <= 0))
317                 msg->msg_flags |= MSG_CTRUNC;
318
319         /*
320          * All of the files that fit in the message have had their
321          * usage counts incremented, so we just free the list.
322          */
323         __scm_destroy(scm);
324 }
325 EXPORT_SYMBOL(scm_detach_fds);
326
327 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
328 {
329         struct scm_fp_list *new_fpl;
330         int i;
331
332         if (!fpl)
333                 return NULL;
334
335         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
336                           GFP_KERNEL);
337         if (new_fpl) {
338                 for (i = 0; i < fpl->count; i++)
339                         get_file(fpl->fp[i]);
340                 new_fpl->max = new_fpl->count;
341         }
342         return new_fpl;
343 }
344 EXPORT_SYMBOL(scm_fp_dup);