linux: Add fallback for 64-bit time_t SO_TIMESTAMP{NS}

The recvmsg handling is more complicated because it requires check the
returned kernel control message and make some convertions.  For
!__ASSUME_TIME64_SYSCALLS it converts the first 32-bit time SO_TIMESTAMP
or SO_TIMESTAMPNS and appends it to the control buffer if has extra
space or returns MSG_CTRUNC otherwise.  The 32-bit time field is kept
as-is.

Calls with __TIMESIZE=32 will see the converted 64-bit time control
messages as spurious control message of unknown type.  Calls with
__TIMESIZE=64 running on pre-time64 kernels will see the original
message as a spurious control ones of unknown typ while running on
kernel with native 64-bit time support will only see the time64 version
of the control message.

Checked on x86_64-linux-gnu and i686-linux-gnu (on 5.4 and on 4.15
kernel).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 95 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/convert_scm_timestamps.c b/sysdeps/unix/sysv/linux/convert_scm_timestamps.c
new file mode 100644
index 0000000000..d75a4618dd
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/convert_scm_timestamps.c
@@ -0,0 +1,95 @@
+/* Socket timestamp conversion routines.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <kernel-features.h>
+
+#ifndef __ASSUME_TIME64_SYSCALLS
+# include <stdint.h>
+# include <string.h>
+# include <sys/socket.h>
+# include <socket-constants-time64.h>
+
+/* It converts the first SO_TIMESTAMP or SO_TIMESTAMPNS with 32-bit time and
+   appends it to the control buffer.  The 32-bit time field is kept as-is.
+
+   Calls with __TIMESIZE=32 will see the converted 64-bit time control
+   messages as spurious control message of unknown type.
+
+   Calls with __TIMESIZE=64 running on pre-time64 kernels will see the
+   original message as a spurious control ones of unknown typ while running
+   on kernel with native 64-bit time support will only see the time64 version
+   of the control message.  */
+void
+__convert_scm_timestamps (struct msghdr *msg, socklen_t msgsize)
+{
+  if (msg->msg_control == NULL || msg->msg_controllen == 0)
+    return;
+
+  /* The returned control message format for SO_TIMESTAMP_NEW is a
+     'struct __kernel_sock_timeval' while for SO_TIMESTAMPNS_NEW is a
+     'struct __kernel_timespec'.  In either case it is two uint64_t
+     members.  */
+  uint64_t tvts[2];
+
+  struct cmsghdr *cmsg, *last = NULL;
+  int type = 0;
+
+  for (cmsg = CMSG_FIRSTHDR (msg);
+       cmsg != NULL;
+       cmsg = CMSG_NXTHDR (msg, cmsg))
+    {
+      if (cmsg->cmsg_level != SOL_SOCKET)
+	continue;
+
+      switch (cmsg->cmsg_type)
+	{
+	case COMPAT_SO_TIMESTAMP_OLD:
+	  if (type != 0)
+	    break;
+	  type = COMPAT_SO_TIMESTAMP_NEW;
+	  goto common;
+
+	case COMPAT_SO_TIMESTAMPNS_OLD:
+	  type = COMPAT_SO_TIMESTAMPNS_NEW;
+
+	/* fallthrough  */
+	common:
+	  memcpy (tvts, CMSG_DATA (cmsg), sizeof (tvts));
+	  break;
+	}
+
+      last = cmsg;
+    }
+
+  if (last == NULL || type == 0)
+    return;
+
+  if (CMSG_SPACE (sizeof tvts) > msgsize - msg->msg_controllen)
+    {
+      msg->msg_flags |= MSG_CTRUNC;
+      return;
+    }
+
+  msg->msg_controllen += CMSG_SPACE (sizeof tvts);
+  cmsg = CMSG_NXTHDR(msg, last);
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = type;
+  cmsg->cmsg_len = CMSG_LEN (sizeof tvts);
+  memcpy (CMSG_DATA (cmsg), tvts, sizeof tvts);
+}
+#endif