[net PATCH] net: tls, fix sk_write_space NULL write when tx disabled

[John Fastabend <john.fastabend@gmail.com>]

The ctx->sk_write_space pointer is only set when TLS tx mode is enabled.
When running without TX mode its a null pointer but we still set the
sk sk_write_space pointer on close().

Fix the close path to only overwrite sk->sk_write_space when the current
pointer is to the tls_write_space function indicating the tls module should
clean it up properly as well.

Reported-by: Hillf Danton <hdanton@sina.com>
Cc: Ying Xue <ying.xue@windriver.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Fixes: 57c722e932cfb ("net/tls: swap sk_write_space on close")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/tls/tls_main.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
index ce6ef56a65ef..43252a801c3f 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -308,7 +308,8 @@ static void tls_sk_proto_close(struct sock *sk, long timeout)
 	if (free_ctx)
 		icsk->icsk_ulp_data = NULL;
 	sk->sk_prot = ctx->sk_proto;
-	sk->sk_write_space = ctx->sk_write_space;
+	if (sk->sk_write_space == tls_write_space)
+		sk->sk_write_space = ctx->sk_write_space;
 	write_unlock_bh(&sk->sk_callback_lock);
 	release_sock(sk);
 	if (ctx->tx_conf == TLS_SW)