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Linux/net/core/scm.c

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  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                 fpl->user = NULL;
 91         }
 92         fpp = &fpl->fp[fpl->count];
 93 
 94         if (fpl->count + num > fpl->max)
 95                 return -EINVAL;
 96 
 97         /*
 98          *      Verify the descriptors and increment the usage count.
 99          */
100 
101         for (i=0; i< num; i++)
102         {
103                 int fd = fdp[i];
104                 struct file *file;
105 
106                 if (fd < 0 || !(file = fget_raw(fd)))
107                         return -EBADF;
108                 *fpp++ = file;
109                 fpl->count++;
110         }
111 
112         if (!fpl->user)
113                 fpl->user = get_uid(current_user());
114 
115         return num;
116 }
117 
118 void __scm_destroy(struct scm_cookie *scm)
119 {
120         struct scm_fp_list *fpl = scm->fp;
121         int i;
122 
123         if (fpl) {
124                 scm->fp = NULL;
125                 for (i=fpl->count-1; i>=0; i--)
126                         fput(fpl->fp[i]);
127                 free_uid(fpl->user);
128                 kfree(fpl);
129         }
130 }
131 EXPORT_SYMBOL(__scm_destroy);
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                         if (!sock->ops || sock->ops->family != PF_UNIX)
160                                 goto error;
161                         err=scm_fp_copy(cmsg, &p->fp);
162                         if (err<0)
163                                 goto error;
164                         break;
165                 case SCM_CREDENTIALS:
166                 {
167                         struct ucred creds;
168                         kuid_t uid;
169                         kgid_t gid;
170                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
171                                 goto error;
172                         memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
173                         err = scm_check_creds(&creds);
174                         if (err)
175                                 goto error;
176 
177                         p->creds.pid = creds.pid;
178                         if (!p->pid || pid_vnr(p->pid) != creds.pid) {
179                                 struct pid *pid;
180                                 err = -ESRCH;
181                                 pid = find_get_pid(creds.pid);
182                                 if (!pid)
183                                         goto error;
184                                 put_pid(p->pid);
185                                 p->pid = pid;
186                         }
187 
188                         err = -EINVAL;
189                         uid = make_kuid(current_user_ns(), creds.uid);
190                         gid = make_kgid(current_user_ns(), creds.gid);
191                         if (!uid_valid(uid) || !gid_valid(gid))
192                                 goto error;
193 
194                         p->creds.uid = uid;
195                         p->creds.gid = gid;
196                         break;
197                 }
198                 default:
199                         goto error;
200                 }
201         }
202 
203         if (p->fp && !p->fp->count)
204         {
205                 kfree(p->fp);
206                 p->fp = NULL;
207         }
208         return 0;
209 
210 error:
211         scm_destroy(p);
212         return err;
213 }
214 EXPORT_SYMBOL(__scm_send);
215 
216 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
217 {
218         struct cmsghdr __user *cm
219                 = (__force struct cmsghdr __user *)msg->msg_control;
220         struct cmsghdr cmhdr;
221         int cmlen = CMSG_LEN(len);
222         int err;
223 
224         if (MSG_CMSG_COMPAT & msg->msg_flags)
225                 return put_cmsg_compat(msg, level, type, len, data);
226 
227         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
228                 msg->msg_flags |= MSG_CTRUNC;
229                 return 0; /* XXX: return error? check spec. */
230         }
231         if (msg->msg_controllen < cmlen) {
232                 msg->msg_flags |= MSG_CTRUNC;
233                 cmlen = msg->msg_controllen;
234         }
235         cmhdr.cmsg_level = level;
236         cmhdr.cmsg_type = type;
237         cmhdr.cmsg_len = cmlen;
238 
239         err = -EFAULT;
240         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
241                 goto out;
242         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
243                 goto out;
244         cmlen = CMSG_SPACE(len);
245         if (msg->msg_controllen < cmlen)
246                 cmlen = msg->msg_controllen;
247         msg->msg_control += cmlen;
248         msg->msg_controllen -= cmlen;
249         err = 0;
250 out:
251         return err;
252 }
253 EXPORT_SYMBOL(put_cmsg);
254 
255 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
256 {
257         struct cmsghdr __user *cm
258                 = (__force struct cmsghdr __user*)msg->msg_control;
259 
260         int fdmax = 0;
261         int fdnum = scm->fp->count;
262         struct file **fp = scm->fp->fp;
263         int __user *cmfptr;
264         int err = 0, i;
265 
266         if (MSG_CMSG_COMPAT & msg->msg_flags) {
267                 scm_detach_fds_compat(msg, scm);
268                 return;
269         }
270 
271         if (msg->msg_controllen > sizeof(struct cmsghdr))
272                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
273                          / sizeof(int));
274 
275         if (fdnum < fdmax)
276                 fdmax = fdnum;
277 
278         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
279              i++, cmfptr++)
280         {
281                 struct socket *sock;
282                 int new_fd;
283                 err = security_file_receive(fp[i]);
284                 if (err)
285                         break;
286                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
287                                           ? O_CLOEXEC : 0);
288                 if (err < 0)
289                         break;
290                 new_fd = err;
291                 err = put_user(new_fd, cmfptr);
292                 if (err) {
293                         put_unused_fd(new_fd);
294                         break;
295                 }
296                 /* Bump the usage count and install the file. */
297                 sock = sock_from_file(fp[i], &err);
298                 if (sock) {
299                         sock_update_netprioidx(sock->sk);
300                         sock_update_classid(sock->sk);
301                 }
302                 fd_install(new_fd, get_file(fp[i]));
303         }
304 
305         if (i > 0)
306         {
307                 int cmlen = CMSG_LEN(i*sizeof(int));
308                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
309                 if (!err)
310                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
311                 if (!err)
312                         err = put_user(cmlen, &cm->cmsg_len);
313                 if (!err) {
314                         cmlen = CMSG_SPACE(i*sizeof(int));
315                         if (msg->msg_controllen < cmlen)
316                                 cmlen = msg->msg_controllen;
317                         msg->msg_control += cmlen;
318                         msg->msg_controllen -= cmlen;
319                 }
320         }
321         if (i < fdnum || (fdnum && fdmax <= 0))
322                 msg->msg_flags |= MSG_CTRUNC;
323 
324         /*
325          * All of the files that fit in the message have had their
326          * usage counts incremented, so we just free the list.
327          */
328         __scm_destroy(scm);
329 }
330 EXPORT_SYMBOL(scm_detach_fds);
331 
332 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
333 {
334         struct scm_fp_list *new_fpl;
335         int i;
336 
337         if (!fpl)
338                 return NULL;
339 
340         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
341                           GFP_KERNEL);
342         if (new_fpl) {
343                 for (i = 0; i < fpl->count; i++)
344                         get_file(fpl->fp[i]);
345                 new_fpl->max = new_fpl->count;
346                 new_fpl->user = get_uid(fpl->user);
347         }
348         return new_fpl;
349 }
350 EXPORT_SYMBOL(scm_fp_dup);
351 

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