From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net] tcp: fix return value for partial writes
Date: Thu, 03 Nov 2016 16:12:53 -0400 (EDT)
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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 02 Nov 2016 14:41:50 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> After my commit, tcp_sendmsg() might restart its loop after
> processing socket backlog.
> 
> If sk_err is set, we blindly return an error, even though we
> copied data to user space before.
> 
> We should instead return number of bytes that could be copied,
> otherwise user space might resend data and corrupt the stream.
> 
> This might happen if another thread is using recvmsg(MSG_ERRQUEUE)
> to process timestamps.
> 
> Issue was diagnosed by Soheil and Willem, big kudos to them !
> 
> Fixes: d41a69f1d390f ("tcp: make tcp_sendmsg() aware of socket backlog")
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied and queued up for -stable.