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