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 #include <net/cls_cgroup.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         kuid_t uid = make_kuid(cred->user_ns, creds->uid);
  50         kgid_t gid = make_kgid(cred->user_ns, creds->gid);
  51
  52         if (!uid_valid(uid) || !gid_valid(gid))
  53                 return -EINVAL;
  54
  55         if ((creds->pid == task_tgid_vnr(current) || nsown_capable(CAP_SYS_ADMIN)) &&
  56             ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
  57               uid_eq(uid, cred->suid)) || nsown_capable(CAP_SETUID)) &&
  58             ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
  59               gid_eq(gid, cred->sgid)) || nsown_capable(CAP_SETGID))) {
  60                return 0;
  61         }
  62         return -EPERM;
  63 }
  64
  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 - CMSG_ALIGN(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);
  83                 if (!fpl)
  84                         return -ENOMEM;
  85                 *fplp = fpl;
  86                 fpl->count = 0;
  87                 fpl->max = SCM_MAX_FD;
  88         }
  89         fpp = &fpl->fp[fpl->count];
  90
  91         if (fpl->count + num > fpl->max)
  92                 return -EINVAL;
  93
  94         /*
  95          *      Verify the descriptors and increment the usage count.
  96          */
  97
  98         for (i=0; i< num; i++)
  99         {
 100                 int fd = fdp[i];
 101                 struct file *file;
 102
 103                 if (fd < 0 || !(file = fget_raw(fd)))
 104                         return -EBADF;
 105                 *fpp++ = file;
 106                 fpl->count++;
 107         }
 108         return num;
 109 }
 110
 111 void __scm_destroy(struct scm_cookie *scm)
 112 {
 113         struct scm_fp_list *fpl = scm->fp;
 114         int i;
 115
 116         if (fpl) {
 117                 scm->fp = NULL;
 118                 for (i=fpl->count-1; i>=0; i--)
 119                         fput(fpl->fp[i]);
 120                 kfree(fpl);
 121         }
 122 }
 123 EXPORT_SYMBOL(__scm_destroy);
 124
 125 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 126 {
 127         struct cmsghdr *cmsg;
 128         int err;
 129
 130         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 131         {
 132                 err = -EINVAL;
 133
 134                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 135                 /* The first check was omitted in <= 2.2.5. The reasoning was
 136                    that parser checks cmsg_len in any case, so that
 137                    additional check would be work duplication.
 138                    But if cmsg_level is not SOL_SOCKET, we do not check
 139                    for too short ancillary data object at all! Oops.
 140                    OK, let's add it...
 141                  */
 142                 if (!CMSG_OK(msg, cmsg))
 143                         goto error;
 144
 145                 if (cmsg->cmsg_level != SOL_SOCKET)
 146                         continue;
 147
 148                 switch (cmsg->cmsg_type)
 149                 {
 150                 case SCM_RIGHTS:
 151                         if (!sock->ops || sock->ops->family != PF_UNIX)
 152                                 goto error;
 153                         err=scm_fp_copy(cmsg, &p->fp);
 154                         if (err<0)
 155                                 goto error;
 156                         break;
 157                 case SCM_CREDENTIALS:
 158                 {
 159                         struct ucred creds;
 160                         kuid_t uid;
 161                         kgid_t gid;
 162                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 163                                 goto error;
 164                         memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 165                         err = scm_check_creds(&creds);
 166                         if (err)
 167                                 goto error;
 168
 169                         p->creds.pid = creds.pid;
 170                         if (!p->pid || pid_vnr(p->pid) != creds.pid) {
 171                                 struct pid *pid;
 172                                 err = -ESRCH;
 173                                 pid = find_get_pid(creds.pid);
 174                                 if (!pid)
 175                                         goto error;
 176                                 put_pid(p->pid);
 177                                 p->pid = pid;
 178                         }
 179
 180                         err = -EINVAL;
 181                         uid = make_kuid(current_user_ns(), creds.uid);
 182                         gid = make_kgid(current_user_ns(), creds.gid);
 183                         if (!uid_valid(uid) || !gid_valid(gid))
 184                                 goto error;
 185
 186                         p->creds.uid = uid;
 187                         p->creds.gid = gid;
 188
 189                         if (!p->cred ||
 190                             !uid_eq(p->cred->euid, uid) ||
 191                             !gid_eq(p->cred->egid, gid)) {
 192                                 struct cred *cred;
 193                                 err = -ENOMEM;
 194                                 cred = prepare_creds();
 195                                 if (!cred)
 196                                         goto error;
 197
 198                                 cred->uid = cred->euid = uid;
 199                                 cred->gid = cred->egid = gid;
 200                                 if (p->cred)
 201                                         put_cred(p->cred);
 202                                 p->cred = cred;
 203                         }
 204                         break;
 205                 }
 206                 default:
 207                         goto error;
 208                 }
 209         }
 210
 211         if (p->fp && !p->fp->count)
 212         {
 213                 kfree(p->fp);
 214                 p->fp = NULL;
 215         }
 216         return 0;
 217
 218 error:
 219         scm_destroy(p);
 220         return err;
 221 }
 222 EXPORT_SYMBOL(__scm_send);
 223
 224 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 225 {
 226         struct cmsghdr __user *cm
 227                 = (__force struct cmsghdr __user *)msg->msg_control;
 228         struct cmsghdr cmhdr;
 229         int cmlen = CMSG_LEN(len);
 230         int err;
 231
 232         if (MSG_CMSG_COMPAT & msg->msg_flags)
 233                 return put_cmsg_compat(msg, level, type, len, data);
 234
 235         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 236                 msg->msg_flags |= MSG_CTRUNC;
 237                 return 0; /* XXX: return error? check spec. */
 238         }
 239         if (msg->msg_controllen < cmlen) {
 240                 msg->msg_flags |= MSG_CTRUNC;
 241                 cmlen = msg->msg_controllen;
 242         }
 243         cmhdr.cmsg_level = level;
 244         cmhdr.cmsg_type = type;
 245         cmhdr.cmsg_len = cmlen;
 246
 247         err = -EFAULT;
 248         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 249                 goto out;
 250         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 251                 goto out;
 252         cmlen = CMSG_SPACE(len);
 253         if (msg->msg_controllen < cmlen)
 254                 cmlen = msg->msg_controllen;
 255         msg->msg_control += cmlen;
 256         msg->msg_controllen -= cmlen;
 257         err = 0;
 258 out:
 259         return err;
 260 }
 261 EXPORT_SYMBOL(put_cmsg);
 262
 263 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 264 {
 265         struct cmsghdr __user *cm
 266                 = (__force struct cmsghdr __user*)msg->msg_control;
 267
 268         int fdmax = 0;
 269         int fdnum = scm->fp->count;
 270         struct file **fp = scm->fp->fp;
 271         int __user *cmfptr;
 272         int err = 0, i;
 273
 274         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 275                 scm_detach_fds_compat(msg, scm);
 276                 return;
 277         }
 278
 279         if (msg->msg_controllen > sizeof(struct cmsghdr))
 280                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 281                          / sizeof(int));
 282
 283         if (fdnum < fdmax)
 284                 fdmax = fdnum;
 285
 286         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 287              i++, cmfptr++)
 288         {
 289                 struct socket *sock;
 290                 int new_fd;
 291                 err = security_file_receive(fp[i]);
 292                 if (err)
 293                         break;
 294                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 295                                           ? O_CLOEXEC : 0);
 296                 if (err < 0)
 297                         break;
 298                 new_fd = err;
 299                 err = put_user(new_fd, cmfptr);
 300                 if (err) {
 301                         put_unused_fd(new_fd);
 302                         break;
 303                 }
 304                 /* Bump the usage count and install the file. */
 305                 sock = sock_from_file(fp[i], &err);
 306                 if (sock) {
 307                         sock_update_netprioidx(sock->sk, current);
 308                         sock_update_classid(sock->sk, current);
 309                 }
 310                 fd_install(new_fd, get_file(fp[i]));
 311         }
 312
 313         if (i > 0)
 314         {
 315                 int cmlen = CMSG_LEN(i*sizeof(int));
 316                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 317                 if (!err)
 318                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 319                 if (!err)
 320                         err = put_user(cmlen, &cm->cmsg_len);
 321                 if (!err) {
 322                         cmlen = CMSG_SPACE(i*sizeof(int));
 323                         msg->msg_control += cmlen;
 324                         msg->msg_controllen -= cmlen;
 325                 }
 326         }
 327         if (i < fdnum || (fdnum && fdmax <= 0))
 328                 msg->msg_flags |= MSG_CTRUNC;
 329
 330         /*
 331          * All of the files that fit in the message have had their
 332          * usage counts incremented, so we just free the list.
 333          */
 334         __scm_destroy(scm);
 335 }
 336 EXPORT_SYMBOL(scm_detach_fds);
 337
 338 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 339 {
 340         struct scm_fp_list *new_fpl;
 341         int i;
 342
 343         if (!fpl)
 344                 return NULL;
 345
 346         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 347                           GFP_KERNEL);
 348         if (new_fpl) {
 349                 for (i = 0; i < fpl->count; i++)
 350                         get_file(fpl->fp[i]);
 351                 new_fpl->max = new_fpl->count;
 352         }
 353         return new_fpl;
 354 }
 355 EXPORT_SYMBOL(scm_fp_dup);