linux-kernel - [PATCH] af_unix: fix regression in read after shutdown

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Date:   Fri, 19 Nov 2021 13:05:21 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     "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>
CC:     <kernel@...s.com>,
        Vincent Whitchurch <vincent.whitchurch@...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: [PATCH] af_unix: fix regression in read after shutdown

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.

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),
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.

Fixes: d0c6416bd7091647f60 ("unix: Fix an issue in unix_shutdown causing the other end read/write failures")
Link: https://lore.kernel.org/lkml/20211111140000.GA10779@axis.com/
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
---
 net/unix/af_unix.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 78e08e82c08c..b0bfc78e421c 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2882,9 +2882,6 @@ static int unix_shutdown(struct socket *sock, int mode)

 	unix_state_lock(sk);
 	sk->sk_shutdown |= mode;
-	if ((sk->sk_type == SOCK_STREAM || sk->sk_type == SOCK_SEQPACKET) &&
-	    mode == SHUTDOWN_MASK)
-		sk->sk_state = TCP_CLOSE;
 	other = unix_peer(sk);
 	if (other)
 		sock_hold(other);
-- 
2.33.1