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 d4a1875ddd1eb7ef ("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: 1da06ea85c6fba572d2 ("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@axis.com>
Tested-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 78e08e82c08c423ff2112fcef9e27995a6d39984..b0bfc78e421ceef27a4466ceac6be09e7a50476a 100644 (file)
--- 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);