lib/passfd.c

   1 /* Copyright (C) 2011-2025 Free Software Foundation, Inc.
   2
   3    This file is free software: you can redistribute it and/or modify
   4    it under the terms of the GNU Lesser General Public License as
   5    published by the Free Software Foundation; either version 2.1 of the
   6    License, or (at your option) any later version.
   7
   8    This file is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU Lesser General Public License for more details.
  12
  13    You should have received a copy of the GNU Lesser General Public License
  14    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  15
  16 #include <config.h>
  17
  18 /* Specification.  */
  19 #include "passfd.h"
  20
  21 #include <errno.h>
  22 #include <fcntl.h>
  23 #include <stddef.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <sys/types.h>
  27 #include <unistd.h>
  28
  29 #include <sys/socket.h>
  30
  31 #include "cloexec.h"
  32
  33 /* The code that uses CMSG_FIRSTHDR is enabled on
  34    Linux, Mac OS X, FreeBSD, OpenBSD, NetBSD, AIX, OSF/1, Cygwin.
  35    The code that uses HAVE_STRUCT_MSGHDR_MSG_ACCRIGHTS is enabled on
  36    HP-UX, IRIX, Solaris.  */
  37
  38 /* MSG_CMSG_CLOEXEC is defined only on Linux, as of 2011.  */
  39 #ifndef MSG_CMSG_CLOEXEC
  40 # define MSG_CMSG_CLOEXEC 0
  41 #endif
  42
  43 #if HAVE_SENDMSG
  44 /* sendfd sends the file descriptor fd along the socket
  45    to a process calling recvfd on the other end.
  46
  47    Return 0 on success, or -1 with errno set in case of error.
  48 */
  49 int
  50 sendfd (int sock, int fd)
  51 {
  52   char byte = 0;
  53   struct iovec iov;
  54   struct msghdr msg;
  55 # if defined CMSG_FIRSTHDR && !defined __sgi
  56   struct cmsghdr *cmsg;
  57   char buf[CMSG_SPACE (sizeof fd)];
  58 # endif
  59
  60   /* send at least one char */
  61   memset (&msg, 0, sizeof msg);
  62   iov.iov_base = &byte;
  63   iov.iov_len = 1;
  64   msg.msg_iov = &iov;
  65   msg.msg_iovlen = 1;
  66   msg.msg_name = NULL;
  67   msg.msg_namelen = 0;
  68
  69 # if defined CMSG_FIRSTHDR && !defined __sgi
  70   msg.msg_control = buf;
  71   msg.msg_controllen = sizeof buf;
  72   cmsg = CMSG_FIRSTHDR (&msg);
  73   cmsg->cmsg_level = SOL_SOCKET;
  74   cmsg->cmsg_type = SCM_RIGHTS;
  75   cmsg->cmsg_len = CMSG_LEN (sizeof fd);
  76   /* Initialize the payload: */
  77   memcpy (CMSG_DATA (cmsg), &fd, sizeof fd);
  78   msg.msg_controllen = cmsg->cmsg_len;
  79 # elif HAVE_STRUCT_MSGHDR_MSG_ACCRIGHTS
  80   msg.msg_accrights = &fd;
  81   msg.msg_accrightslen = sizeof fd;
  82 # else
  83   errno = ENOSYS;
  84   return -1;
  85 # endif
  86
  87   if (sendmsg (sock, &msg, 0) != iov.iov_len)
  88     return -1;
  89   return 0;
  90 }
  91 #else
  92 int
  93 sendfd (_GL_UNUSED int sock, _GL_UNUSED int fd)
  94 {
  95   errno = ENOSYS;
  96   return -1;
  97 }
  98 #endif
  99
 100
 101 #if HAVE_RECVMSG
 102 /* recvfd receives a file descriptor through the socket.
 103    The flags are a bitmask, possibly including O_CLOEXEC (defined in <fcntl.h>).
 104
 105    Return the fd on success, or -1 with errno set in case of error.
 106 */
 107 int
 108 recvfd (int sock, int flags)
 109 {
 110   char byte = 0;
 111   struct iovec iov;
 112   struct msghdr msg;
 113   int fd = -1;
 114   ssize_t len;
 115 # if defined CMSG_FIRSTHDR && !defined __sgi
 116   struct cmsghdr *cmsg;
 117   char buf[CMSG_SPACE (sizeof fd)];
 118   int flags_recvmsg = flags & O_CLOEXEC ? MSG_CMSG_CLOEXEC : 0;
 119 # endif
 120
 121   if ((flags & ~O_CLOEXEC) != 0)
 122     {
 123       errno = EINVAL;
 124       return -1;
 125     }
 126
 127   /* send at least one char */
 128   memset (&msg, 0, sizeof msg);
 129   iov.iov_base = &byte;
 130   iov.iov_len = 1;
 131   msg.msg_iov = &iov;
 132   msg.msg_iovlen = 1;
 133   msg.msg_name = NULL;
 134   msg.msg_namelen = 0;
 135
 136 # if defined CMSG_FIRSTHDR && !defined __sgi
 137   msg.msg_control = buf;
 138   msg.msg_controllen = sizeof buf;
 139   cmsg = CMSG_FIRSTHDR (&msg);
 140   cmsg->cmsg_level = SOL_SOCKET;
 141   cmsg->cmsg_type = SCM_RIGHTS;
 142   cmsg->cmsg_len = CMSG_LEN (sizeof fd);
 143   /* Initialize the payload: */
 144   memcpy (CMSG_DATA (cmsg), &fd, sizeof fd);
 145   msg.msg_controllen = CMSG_SPACE (sizeof fd);
 146
 147   len = recvmsg (sock, &msg, flags_recvmsg);
 148   if (len < 0)
 149     return -1;
 150   if (len == 0)
 151     {
 152       /* fake errno: at end the file is not available */
 153       errno = ENOTCONN;
 154       return -1;
 155     }
 156   cmsg = CMSG_FIRSTHDR (&msg);
 157   /* be paranoiac */
 158   if (cmsg == NULL || cmsg->cmsg_len != CMSG_LEN (sizeof fd)
 159       || cmsg->cmsg_level != SOL_SOCKET || cmsg->cmsg_type != SCM_RIGHTS)
 160     {
 161       errno = EACCES;
 162       return -1;
 163     }
 164
 165   memcpy (&fd, CMSG_DATA (cmsg), sizeof fd);
 166
 167   /* set close-on-exec flag */
 168   if (!MSG_CMSG_CLOEXEC && (flags & O_CLOEXEC))
 169     {
 170       if (set_cloexec_flag (fd, true) < 0)
 171         {
 172           int saved_errno = errno;
 173           (void) close (fd);
 174           errno = saved_errno;
 175           return -1;
 176         }
 177     }
 178
 179 # elif HAVE_STRUCT_MSGHDR_MSG_ACCRIGHTS
 180   msg.msg_accrights = &fd;
 181   msg.msg_accrightslen = sizeof fd;
 182   if (recvmsg (sock, &msg, 0) < 0)
 183     return -1;
 184
 185   /* set close-on-exec flag */
 186   if (flags & O_CLOEXEC)
 187     {
 188       if (set_cloexec_flag (fd, true) < 0)
 189         {
 190           int saved_errno = errno;
 191           close (fd);
 192           errno = saved_errno;
 193           return -1;
 194         }
 195     }
 196
 197   if (fd < 0 && errno == 0)
 198     errno = ENOTCONN;
 199 # else
 200   errno = ENOSYS;
 201 # endif
 202
 203   return fd;
 204 }
 205 #else
 206 int
 207 recvfd (_GL_UNUSED int sock, _GL_UNUSED int flags)
 208 {
 209   errno = ENOSYS;
 210   return -1;
 211 }
 212 #endif