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: 17926a79320a ("[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: 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/af_rxrpc.c | 6 ------
 net/rxrpc/key.c      | 2 +-
 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 0f90272ac254..32ec91fa938f 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -654,9 +654,6 @@ 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;
@@ -664,9 +661,6 @@ static int rxrpc_setsockopt(struct socket *sock, int level, int optname,
 			goto error;
 
 		case RXRPC_SECURITY_KEYRING:
-			ret = -EINVAL;
-			if (rx->key)
-				goto error;
 			ret = -EISCONN;
 			if (rx->sk.sk_state != RXRPC_UNBOUND)
 				goto error;
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 77237a82be3b..6301d79ee35a 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -622,7 +622,7 @@ 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);