netdev - Re: [PATCH] af_unix: fix regression in read after shutdown

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Date:   Tue, 23 Nov 2021 15:45:43 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, kernel@...s.com,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Jiang Wang <jiang.wang@...edance.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH] af_unix: fix regression in read after shutdown

On Fri, Nov 19, 2021 at 01:05:21PM +0100, Vincent Whitchurch wrote:
> On kernels before v5.15, calling read() on a unix socket after
> shutdown(SHUT_RD) or shutdown(SHUT_RDWR) would return the data
> previously written or EOF.  But now, while read() after
> shutdown(SHUT_RD) still behaves the same way, read() after
> shutdown(SHUT_RDWR) always fails with -EINVAL.

Maybe just lift the socket tate check in unix_stream_read_generic()?

> 
> This behaviour change was apparently inadvertently introduced as part of
> a bug fix for a different regression caused by the commit adding sockmap
> support to af_unix, commit 94531cfcbe79c359 ("af_unix: Add
> unix_stream_proto for sockmap").  Those commits, for unclear reasons,
> started setting the socket state to TCP_CLOSE on shutdown(SHUT_RDWR),

Not sure why it is unclear here, for an connection oriented socket, it
can be closed for just one direction, in this case we want to prevent it
from being redirected in sockmap, hence the point of the commits.

> while this state change had previously only been done in
> unix_release_sock().
> 
> Restore the original behaviour.  The sockmap tests in
> tests/selftests/bpf continue to pass after this patch.

Isn't this because we don't have shutdown() in sockmap tests?

Thanks.