rxrpc: Fix key/keyring checks in setsockopt(RXRPC_SECURITY_KEY/KEYRING)

commit 2afd86c upstream.

An AF_RXRPC socket can be both client and server at the same time.  When
sending new calls (ie. it's acting as a client), it uses rx->key to set the
security, and when accepting incoming calls (ie. it's acting as a server),
it uses rx->securities.

setsockopt(RXRPC_SECURITY_KEY) sets rx->key to point to an rxrpc-type key
and setsockopt(RXRPC_SECURITY_KEYRING) sets rx->securities to point to a
keyring of rxrpc_s-type keys.

Now, it should be possible to use both rx->key and rx->securities on the
same socket - but for userspace AF_RXRPC sockets rxrpc_setsockopt()
prevents that.

Fix this by:

 (1) Remove the incorrect check rxrpc_setsockopt(RXRPC_SECURITY_KEYRING)
     makes on rx->key.

 (2) Move the check that rxrpc_setsockopt(RXRPC_SECURITY_KEY) makes on
     rx->key down into rxrpc_request_key().

 (3) Remove rxrpc_request_key()'s check on rx->securities.

This (in combination with a previous patch) pushes the checks down into the
functions that set those pointers and removes the cross-checks that prevent
both key and keyring being set.

Fixes: 17926a7 ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Closes: https://sashiko.dev/#/patchset/20260401105614.1696001-10-dhowells@redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Anderson Nascimento <anderson@allelesecurity.com>
cc: Luxiao Xu <rakukuip@gmail.com>
cc: Yuan Tan <yuantan098@gmail.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260408121252.2249051-16-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: dhowells

net/rxrpc/af_rxrpc.c

@@ -681,19 +681,13 @@ static int rxrpc_setsockopt(struct socket *sock, int level, int optname,
 			goto success;
 
 		case RXRPC_SECURITY_KEY:
-			ret = -EINVAL;
-			if (rx->key)
-				goto error;
 			ret = -EISCONN;
 			if (rx->sk.sk_state != RXRPC_UNBOUND)
 				goto error;
 			ret = rxrpc_request_key(rx, optval, optlen);
 			goto error;
 
 		case RXRPC_SECURITY_KEYRING:
-			ret = -EINVAL;
-			if (rx->key)
-				goto error;
 			ret = -EISCONN;
 			if (rx->sk.sk_state != RXRPC_UNBOUND)
 				goto error;

net/rxrpc/key.c

@@ -452,7 +452,7 @@ int rxrpc_request_key(struct rxrpc_sock *rx, sockptr_t optval, int optlen)
 
 	_enter("");
 
-	if (optlen <= 0 || optlen > PAGE_SIZE - 1 || rx->securities)
+	if (optlen <= 0 || optlen > PAGE_SIZE - 1 || rx->key)
 		return -EINVAL;
 
 	description = memdup_sockptr_nul(optval, optlen);