Fix rxgk_do_verify_authenticator() to check the buffer size before checking
the nonce.

Fixes: 9d1d2b59341f ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)")
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: 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/rxgk.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
index c67e3c2ca871..0d5e654da918 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -1085,6 +1085,9 @@ static int rxgk_do_verify_authenticator(struct rxrpc_connection *conn,
 
 	_enter("");
 
+	if ((end - p) * sizeof(__be32) < 24)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_auth);
 	if (memcmp(p, conn->rxgk.nonce, 20) != 0)
 		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
 					rxgk_abort_resp_bad_nonce);
@@ -1098,7 +1101,7 @@ static int rxgk_do_verify_authenticator(struct rxrpc_connection *conn,
 	p += xdr_round_up(app_len) / sizeof(__be32);
 	if (end - p < 4)
 		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
-					rxgk_abort_resp_short_applen);
+					rxgk_abort_resp_short_auth);
 
 	level	= ntohl(*p++);
 	epoch	= ntohl(*p++);