[PATCH net 4/5] rxrpc: Fix keyring reference count leak in rxrpc_setsockopt()

[David Howells <dhowells@redhat.com>]

From: Anderson Nascimento <anderson@allelesecurity.com>

In rxrpc_setsockopt(), the code checks 'rx->key' when handling the
RXRPC_SECURITY_KEYRING option.  However, this appears to be a logic error.
The code should be checking 'rx->securities' to determine if a keyring has
already been defined for the socket.

Currently, if a user calls setsockopt(RXRPC_SECURITY_KEYRING) multiple
times on the same socket, the check 'if (rx->key)' fails to block
subsequent calls because 'rx->key' has not been defined by the function.
This results in a reference count leak on the keyring.

This patch changes the check to 'rx->securities' to correctly identify if
the socket security keyring has already been configured, returning -EINVAL
on subsequent attempts.

Before the patch:

It shows the keyring reference counter elevated.

$ cat /proc/keys | grep AFSkeys1
27aca8ae I--Q--- 24469721 perm 3f010000  1000  1000 keyring   AFSkeys1: empty
$

After the patch:

The keyring reference counter remains stable and subsequent calls return an
error:

$ ./poc
setsockopt: Invalid argument
$

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Signed-off-by: Anderson Nascimento <anderson@allelesecurity.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
cc: Marc Dionne <marc.dionne@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/af_rxrpc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 0f90272ac254..0b7ed99a3025 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -665,7 +665,7 @@ static int rxrpc_setsockopt(struct socket *sock, int level, int optname,
 
 		case RXRPC_SECURITY_KEYRING:
 			ret = -EINVAL;
-			if (rx->key)
+			if (rx->securities)
 				goto error;
 			ret = -EISCONN;
 			if (rx->sk.sk_state != RXRPC_UNBOUND)