Hi netdev folk!

Commit c14ac9451c34832554db33386a4393be8bba3a7b
broke pulseaudio (PA) over TCP.

PA does unusual thing: it calls
    sendmsg(cmsg_type=SCM_CREDENTIALS)
on a TCP socket. It's not a new PA behaviour though.

Originally reported as PA bug (has more details)
    https://bugs.freedesktop.org/show_bug.cgi?id=96873

It looks like kernel used to ignore control messages
but now it does not:
    
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/diff/net/ipv4/tcp.c?id=c14ac9451c34832554db33386a4393be8bba3a7b

+       if (msg->msg_controllen) {
+               err = sock_cmsg_send(sk, msg, &sockc);
+               if (unlikely(err)) {
+                       err = -EINVAL;
+                       goto out_err;
+               }
+       }

This change breaks streaming of pulse clients.

Pulseaudio will be fixed at some point.

But kernel change does not look like intentional
breakage of old behaviour.

Perhaps kernel should have a grace period and only
warn about unsupported control messages for a socket?

Last working kernel: v4.6

Thanks!

-- 

  Sergei

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