Re: [PATCH v5 2/3] linux: Fix ancillary 64-bit time timestamp conversion (BZ #28349, BZ#28350)

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 09/30/2022 11:47, Szabolcs Nagy via Libc-alpha wrote:
> The 01/27/2022 17:15, Adhemerval Zanella via Libc-alpha wrote:
> > The __convert_scm_timestamps only updates the control message last
> > pointer for SOL_SOCKET type, so if the message control buffer contains
> > multiple ancillary message types the converted timestamp one might
> > overwrite a valid message.
> > 
> > The test checks if the extra ancillary space is correctly handled
> > by recvmsg/recvmmsg, where if there is no extra space for the 64-bit
> > time_t converted message the control buffer should be marked with
> > MSG_TRUNC.  It also check if recvmsg/recvmmsg handle correctly multiple
> > ancillary data.
> > 
> > Checked on x86_64-linux and on i686-linux-gnu on both 5.11 and
> > 4.15 kernel.
> > 
> > Co-authored-by: Fabian Vogt <fvogt@suse.de>
> 
> note: the time64 recvmsg test started to fail on 32bit
> arm after i updated my aarch64 kernel to 5.18

sorry the kernel is
Linux 8a7948402d35 5.15.0-48-generic #54~20.04.1-Ubuntu SMP Thu Sep 1 16:20:53 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux

> 
> FAIL: socket/tst-socket-timestamp-time64
> 
> ../sysdeps/unix/sysv/linux/tst-socket-timestamp.c:136: numeric comparison failure
>    left: 0 (0x0); from: timestamp
>   right: 1 (0x1); from: exp_timestamp
> 
> 
> > +static void
> > +do_recvmsg_slack_ancillary (bool use_multi_call, int s, void *cmsg,
> > +			    size_t slack, size_t tsize, int exp_payload)
> > +{
> > +  int payload;
> > +  struct iovec iov =
> > +    {
> > +      .iov_base = &payload,
> > +      .iov_len = sizeof (payload)
> > +    };
> > +  size_t msg_controllen = CMSG_SPACE (tsize) + slack;
> > +  char *msg_control = cmsg - msg_controllen;
> > +  memset (msg_control, 0x55, msg_controllen);
> > +  struct mmsghdr mmhdr =
> > +    {
> > +      .msg_hdr =
> > +      {
> > +        .msg_name = NULL,
> > +        .msg_namelen = 0,
> > +        .msg_iov = &iov,
> > +        .msg_iovlen = 1,
> > +        .msg_control = msg_control,
> > +        .msg_controllen = msg_controllen
> > +      },
> > +    };
> > +
> > +  int r;
> > +  if (use_multi_call)
> > +    {
> > +      r = recvmmsg (s, &mmhdr, 1, 0, NULL);
> > +      if (r >= 0)
> > +	r = mmhdr.msg_len;
> > +    }
> > +  else
> > +    r = recvmsg (s, &mmhdr.msg_hdr, 0);
> > +  TEST_COMPARE (r, sizeof (int));
> > +  TEST_COMPARE (payload, exp_payload);
> > +
> > +  if (cmsg == NULL)
> > +    return;
> > +
> > +  /* A timestamp is expected if 32-bit timestamp are used (support in every
> > +     configuration) or if underlying kernel support 64-bit timestamps.
> > +     Otherwise recvmsg will need extra space do add the 64-bit timestamp.  */
> > +  bool exp_timestamp;
> > +  if (sizeof (time_t) == 4 || support_64_timestamp)
> > +    exp_timestamp = true;
> > +   else
> > +    exp_timestamp = slack >= CMSG_SPACE (tsize);
> > +
> > +  bool timestamp = false;
> > +  for (struct cmsghdr *cmsg = CMSG_FIRSTHDR (&mmhdr.msg_hdr);
> > +       cmsg != NULL;
> > +       cmsg = CMSG_NXTHDR (&mmhdr.msg_hdr, cmsg))
> > +    {
> > +      if (cmsg->cmsg_level != SOL_SOCKET)
> > +	continue;
> > +      if (cmsg->cmsg_type == SCM_TIMESTAMP
> > +	  && cmsg->cmsg_len == CMSG_LEN (sizeof (struct timeval)))
> 
> 
> in strace i see
> 
> recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\0\0\0\0", iov_len=4}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_TIMESTAMP, cmsg_data={tv_sec=1664533412, tv_usec=56794}}], msg_controllen=20, msg_flags=0}, 0) = 4
> 
> i.e. cmsg->cmsg_len == 20, but CMSG_LEN (sizeof (struct timeval)) is 28.
> 
> in the loop sometimes i also see a second cmsg where
> cmsg->cmsg_type == SO_TIMESTAMP_NEW and cmsg->cmsg_len == 28,
> but then the type does not match.
> 
> same behaviour with recvmmsg_time64 (but my strace is too
> old to show that).
> 
> not sure how to debug this further.
> 
> > +	{
> > +	  struct timeval tv;
> > +	  memcpy (&tv, CMSG_DATA (cmsg), sizeof (tv));
> > +	  if (test_verbose)
> > +	    printf ("SCM_TIMESTAMP:   {%jd, %jd}\n", (intmax_t)tv.tv_sec,
> > +		    (intmax_t)tv.tv_usec);
> > +	  timestamp = true;
> > +	}
> > +      else if (cmsg->cmsg_type == SCM_TIMESTAMPNS
> > +	       && cmsg->cmsg_len == CMSG_LEN (sizeof (struct timespec)))
> > +	{
> > +	  struct timespec ts;
> > +	  memcpy (&ts, CMSG_DATA (cmsg), sizeof (ts));
> > +	  if (test_verbose)
> > +	    printf ("SCM_TIMESTAMPNS: {%jd, %jd}\n", (intmax_t)ts.tv_sec,
> > +		    (intmax_t)ts.tv_nsec);
> > +	  timestamp = true;
> > +	}
> > +    }
> > +
> > +  TEST_COMPARE (timestamp, exp_timestamp);
> 
> this fails with false != true.