[PATCH net 3/5] rxrpc: Fix UAF in rxgk_issue_challenge()

Fix rxgk_issue_challenge() to free the page containing the challenge
content after invoking the tracepoint as the whdr passed to the tracepoint
points into the page just freed.

Fixes: 9d1d2b59341f ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.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/rxgk.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
index a1ee102abae1..77a67ace1d24 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c

@@ -687,16 +687,17 @@ static int rxgk_issue_challenge(struct rxrpc_connection *conn)
 	ret = do_udp_sendmsg(conn->local->socket, &msg, len);
 	if (ret > 0)
 		rxrpc_peer_mark_tx(conn->peer);
-	__free_page(page);
 
 	if (ret < 0) {
 		trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
 				    rxrpc_tx_point_rxgk_challenge);
+		__free_page(page);
 		return -EAGAIN;
 	}
 
 	trace_rxrpc_tx_packet(conn->debug_id, whdr,
 			      rxrpc_tx_point_rxgk_challenge);
+	__free_page(page);
 	_leave(" = 0");
 	return 0;
 }