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, 17 insertions, 6 deletions

diff --git a/sysdeps/unix/sysv/linux/recvmsg.c b/sysdeps/unix/sysv/linux/recvmsg.c
index b209b4ad99..a2a600228b 100644
--- a/sysdeps/unix/sysv/linux/recvmsg.c
+++ b/sysdeps/unix/sysv/linux/recvmsg.c
@@ -19,16 +19,27 @@
 #include <sys/socket.h>
 #include <sysdep-cancel.h>
 #include <socketcall.h>
-#include <shlib-compat.h>
 
 ssize_t
 __libc_recvmsg (int fd, struct msghdr *msg, int flags)
 {
-# ifdef __ASSUME_RECVMSG_SYSCALL
-  return SYSCALL_CANCEL (recvmsg, fd, msg, flags);
-# else
-  return SOCKETCALL_CANCEL (recvmsg, fd, msg, flags);
-# endif
+  ssize_t r;
+#ifndef __ASSUME_TIME64_SYSCALLS
+  socklen_t orig_controllen = msg->msg_controllen;
+#endif
+
+#ifdef __ASSUME_RECVMSG_SYSCALL
+  r = SYSCALL_CANCEL (recvmsg, fd, msg, flags);
+#else
+  r = SOCKETCALL_CANCEL (recvmsg, fd, msg, flags);
+#endif
+
+#ifndef __ASSUME_TIME64_SYSCALLS
+  if (r >= 0)
+    __convert_scm_timestamps (msg, orig_controllen);
+#endif
+
+  return r;
 }
 weak_alias (__libc_recvmsg, recvmsg)
 weak_alias (__libc_recvmsg, __recvmsg)