sysdeps/unix/sysv/linux/sendmsg.c

   1 /* Copyright (C) 1998 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <sys/socket.h>
  20 #include <errno.h>
  21 #include <unistd.h>
  22
  23 #include <asm/posix_types.h>
  24
  25 /* The kernel expects this structure in SCM_CREDS messages.
  26  * Note: sizeof(struct __kernel_ucred) <= sizeof(struct cmsgcred) must hold.
  27  */
  28 struct __kernel_ucred
  29 {
  30   __kernel_pid_t pid;
  31   __kernel_uid_t uid;
  32   __kernel_gid_t gid;
  33 };
  34
  35 extern int __syscall_sendmsg (int, const struct msghdr *, int);
  36
  37 /* Send a message described by MESSAGE on socket FD.
  38    Returns the number of bytes sent, or -1 for errors.  */
  39 int
  40 __libc_sendmsg (int fd, const struct msghdr *message, int flags)
  41 {
  42   struct cmsghdr *cm;
  43   struct cmsgcred *cc;
  44   struct __kernel_ucred *u;
  45   pid_t pid;
  46
  47   /* Preprocess the message control block for SCM_CREDS. */
  48   cm = CMSG_FIRSTHDR (message);
  49   while (cm)
  50     {
  51       if (cm->cmsg_type == SCM_CREDS)
  52         {
  53           if (cm->cmsg_len < CMSG_SPACE (sizeof (struct cmsgcred)))
  54             {
  55               __set_errno (EINVAL);
  56               return -1;
  57             }
  58
  59           u = (struct __kernel_ucred *) CMSG_DATA (cm);
  60           cc = (struct cmsgcred *) CMSG_DATA (cm);
  61           /* Linux expects the calling process to pass in
  62              its credentials, and sanity checks them.
  63              You can send real, effective, or set- uid and gid.
  64              If the user hasn't filled in the buffer, we default to
  65              real uid and gid. */
  66           pid = __getpid ();
  67           if (cc->cmcred_pid != pid)
  68           {
  69               u->pid = pid;
  70               u->uid = __getuid ();
  71               u->gid = __getgid ();
  72           }
  73           else
  74           {
  75               struct __kernel_ucred v;
  76               v.pid = cc->cmcred_pid;
  77               v.uid = cc->cmcred_uid;
  78               v.gid = cc->cmcred_gid;
  79               u->pid = v.pid;
  80               u->uid = v.uid;
  81               u->gid = v.gid;
  82           }
  83         }
  84       cm = CMSG_NXTHDR ((struct msghdr *) message, cm);
  85     }
  86
  87   return __syscall_sendmsg (fd, message, flags);
  88 }
  89
  90 weak_alias (__libc_sendmsg, __sendmsg)
  91 weak_alias (__libc_sendmsg, sendmsg)