[PATCH net v5 17/21] rxrpc: Fix integer overflow in rxgk_verify_response()

[David Howells]

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 at redhat.com>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: Jeffrey Altman <jaltman at auristor.com>
cc: Eric Dumazet <edumazet at google.com>
cc: "David S. Miller" <davem at davemloft.net>
cc: Jakub Kicinski <kuba at kernel.org>
cc: Paolo Abeni <pabeni at redhat.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: netdev at vger.kernel.org
cc: stable at 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);