In rxgk_verify_response(), there's a potential integer overflow due to
rounding up token_len before checking it, thereby allowing the length check to
be bypassed.

Fix this by checking the unrounded value against len too (len is limited as
the response must fit in a single UDP packet).

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 | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
index 9e4a4ff28913..064c1531fc99 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -1209,7 +1209,8 @@ static int rxgk_verify_response(struct rxrpc_connection *conn,
 
 	token_offset	= offset;
 	token_len	= ntohl(rhdr.token_len);
-	if (xdr_round_up(token_len) + sizeof(__be32) > len)
+	if (token_len > len ||
+	    xdr_round_up(token_len) + sizeof(__be32) > len)
 		goto short_packet;
 
 	trace_rxrpc_rx_response(conn, sp->hdr.serial, 0, sp->hdr.cksum, token_len);