[PATCH 6.18 78/83] rxrpc: Fix integer overflow in rxgk_verify_response()

[Greg Kroah-Hartman]

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells at redhat.com>

commit 699e52180f4231c257821c037ed5c99d5eb0edb8 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 net/rxrpc/rxgk.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -1209,7 +1209,8 @@ static int rxgk_verify_response(struct r
 
 	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);