[PATCH] af_unix: fix regression in read after shutdown

From: Vincent Whitchurch
Date: Fri Nov 19 2021 - 07:05:29 EST

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

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@xxxxxxxx/
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
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)

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)