[glibc/azanella/y2038] linux: Add recvvmsg fallback for 64-bit time_t SO_TIMESTAMP{NS}

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=678a7a2660d815ab5b30db5b4640475868b0d3be

commit 678a7a2660d815ab5b30db5b4640475868b0d3be
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Tue Sep 8 09:08:10 2020 -0300

    linux: Add recvvmsg fallback for 64-bit time_t SO_TIMESTAMP{NS}
    
    Handle the SO_TIMESTAMP{NS} similar to recvmsg: 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.
    
    Also for !__ASSUME_TIME64_SYSCALLS it limits the maximum number of
    'struct mmsghdr *' to IOV_MAX (and also increases the stack size
    requirement to IOV_MAX times sizeof (socklen_t)).  The Linux imposes
    a similar limit to sendmmsg, so bound the array size on recvmmsg is not
    unreasonable.  And this will be used only on older when building with
    32-bit time support.
    
    Checked on x86_64-linux-gnu and i686-linux-gnu (on 5.4 and on 4.15
    kernel).

Diff:
---
 sysdeps/unix/sysv/linux/recvmmsg.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/recvmmsg.c b/sysdeps/unix/sysv/linux/recvmmsg.c
index 672ba20332..5cd107ffa9 100644
--- a/sysdeps/unix/sysv/linux/recvmmsg.c
+++ b/sysdeps/unix/sysv/linux/recvmmsg.c
@@ -44,13 +44,26 @@ __recvmmsg64 (int fd, struct mmsghdr *vmessages, unsigned int vlen, int flags,
       ts32 = valid_timespec64_to_timespec (*timeout);
       pts32 = &ts32;
     }
+
+  socklen_t csize[IOV_MAX];
+  if (vlen > IOV_MAX)
+    vlen = IOV_MAX;
+  for (int i = 0; i < vlen; i++)
+    csize[i] = vmessages[i].msg_hdr.msg_controllen;
+
 # ifdef __ASSUME_RECVMMSG_SYSCALL
   r = SYSCALL_CANCEL (recvmmsg, fd, vmessages, vlen, flags, pts32);
 # else
   r = SOCKETCALL_CANCEL (recvmmsg, fd, vmessages, vlen, flags, pts32);
 # endif
-  if (r >= 0 && timeout != NULL)
-    *timeout = valid_timespec_to_timespec64 (ts32);
+  if (r >= 0)
+    {
+      if (timeout != NULL)
+        *timeout = valid_timespec_to_timespec64 (ts32);
+
+      for (int i=0; i < r; i++)
+        __convert_scm_timestamps (&vmessages[i].msg_hdr, csize[i]);
+    }
 #endif /* __ASSUME_TIME64_SYSCALLS  */
   return r;
 }