sysdeps/unix/sysv/linux/convert_scm_timestamps.c

   1 /* Socket timestamp conversion routines.
   2    Copyright (C) 2021-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <bits/timesize.h>
  20
  21 #if __TIMESIZE != 64
  22 # include <stdint.h>
  23 # include <string.h>
  24 # include <sys/socket.h>
  25 # include <socket-constants-time64.h>
  26 # include <libc-diag.h>
  27
  28 /* It converts the first SO_TIMESTAMP or SO_TIMESTAMPNS with 32-bit time and
  29    appends it to the control buffer.  The 32-bit time field is kept as-is.
  30
  31    Calls with __TIMESIZE=32 will see the converted 64-bit time control
  32    messages as spurious control message of unknown type.
  33
  34    Calls with __TIMESIZE=64 running on pre-time64 kernels will see the
  35    original message as a spurious control ones of unknown typ while running
  36    on kernel with native 64-bit time support will only see the time64 version
  37    of the control message.  */
  38 void
  39 __convert_scm_timestamps (struct msghdr *msg, socklen_t msgsize)
  40 {
  41   if (msg->msg_control == NULL || msg->msg_controllen == 0)
  42     return;
  43
  44   /* The returned control message format for SO_TIMESTAMP_NEW is a
  45      'struct __kernel_sock_timeval' while for SO_TIMESTAMPNS_NEW is a
  46      'struct __kernel_timespec'.  In either case it is two uint64_t
  47      members.  */
  48
  49   /* GCC 6 issues an warning that tvts[0]/tvts[1] maybe be used uninitialized,
  50      however it would be used if type is set to a value different than 0
  51      (done by either COMPAT_SO_TIMESTAMP_OLD or COMPAT_SO_TIMESTAMPNS_OLD)
  52      which will fallthrough to 'common' label.  */
  53   DIAG_PUSH_NEEDS_COMMENT;
  54   DIAG_IGNORE_NEEDS_COMMENT (6, "-Wmaybe-uninitialized");
  55   int64_t tvts[2];
  56   DIAG_POP_NEEDS_COMMENT;
  57   int32_t tmp[2];
  58
  59   struct cmsghdr *cmsg, *last = NULL;
  60   int type = 0;
  61
  62   for (cmsg = CMSG_FIRSTHDR (msg);
  63        cmsg != NULL;
  64        cmsg = CMSG_NXTHDR (msg, cmsg))
  65     {
  66       last = cmsg;
  67
  68       if (cmsg->cmsg_level != SOL_SOCKET)
  69         continue;
  70
  71       switch (cmsg->cmsg_type)
  72         {
  73         case COMPAT_SO_TIMESTAMP_OLD:
  74           if (type != 0)
  75             break;
  76           type = COMPAT_SO_TIMESTAMP_NEW;
  77           goto common;
  78
  79         case COMPAT_SO_TIMESTAMPNS_OLD:
  80           type = COMPAT_SO_TIMESTAMPNS_NEW;
  81
  82         /* fallthrough  */
  83         common:
  84           memcpy (tmp, CMSG_DATA (cmsg), sizeof (tmp));
  85           tvts[0] = tmp[0];
  86           tvts[1] = tmp[1];
  87           break;
  88         }
  89     }
  90
  91   if (type == 0)
  92     return;
  93
  94   if (CMSG_SPACE (sizeof tvts) > msgsize - msg->msg_controllen)
  95     {
  96       msg->msg_flags |= MSG_CTRUNC;
  97       return;
  98     }
  99
 100   /* Zero memory for the new cmsghdr, so reading cmsg_len field
 101      by CMSG_NXTHDR does not trigger UB.  */
 102   memset (msg->msg_control + msg->msg_controllen, 0,
 103           CMSG_SPACE (sizeof tvts));
 104   msg->msg_controllen += CMSG_SPACE (sizeof tvts);
 105   cmsg = CMSG_NXTHDR (msg, last);
 106   cmsg->cmsg_level = SOL_SOCKET;
 107   cmsg->cmsg_type = type;
 108   cmsg->cmsg_len = CMSG_LEN (sizeof tvts);
 109   memcpy (CMSG_DATA (cmsg), tvts, sizeof tvts);
 110 }
 111 #endif