[SRU][Q][PATCH 1/1] rxrpc: Fix integer overflow in rxgk_verify_response()

[Cengiz Can]

From: David Howells <dhowells at redhat.com>

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: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: stable at kernel.org
Link: https://patch.msgid.link/20260408121252.2249051-18-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit 699e52180f4231c257821c037ed5c99d5eb0edb8)
CVE-2026-31633
Assisted-by: kybele:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 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 4062f29caa13..4d2a262b14ce 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -1208,7 +1208,8 @@ 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);
-- 
2.43.0