In rxrpc_new_client_call_for_sendmsg(), a key with no payload is meant to
be substituted for a NULL key pointer, but the variable this is done with
is subsequently not used.

Fix this by using "key" rather than "rx->key" when filling in the
connection parameters.

Note that this only affects direct use of AF_RXRPC; the kAFS filesystem
doesn't use sendmsg() directly and so bypasses the issue.  Further,
AF_RXRPC passes a NULL key in if no key is set, so using an anonymous key
in that manner works.  Since this hasn't been noticed to this point, it
might be better just to remove the "key" variable and the code that sets it
- and, arguably, rxrpc_init_client_call_security() would be a better place
to handle it.

Fixes: 19ffa01c9c45 ("rxrpc: Use structs to hold connection params and protocol info")
Closes: https://sashiko.dev/#/patchset/20260319150150.4189381-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
cc: stable@kernel.org
---
 net/rxrpc/sendmsg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 04f9c5f2dc24..c35de4fd75e3 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -637,7 +637,7 @@ rxrpc_new_client_call_for_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg,
 	memset(&cp, 0, sizeof(cp));
 	cp.local		= rx->local;
 	cp.peer			= peer;
-	cp.key			= rx->key;
+	cp.key			= key;
 	cp.security_level	= rx->min_sec_level;
 	cp.exclusive		= rx->exclusive | p->exclusive;
 	cp.upgrade		= p->upgrade;