[PATCH 6.18 74/83] rxrpc: fix oversized RESPONSE authenticator length check

[Greg Kroah-Hartman]

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

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

From: Keenan Dong <keenanat2000 at gmail.com>

commit a2567217ade970ecc458144b6be469bc015b23e5 upstream.

rxgk_verify_response() decodes auth_len from the packet and is supposed
to verify that it fits in the remaining bytes. The existing check is
inverted, so oversized RESPONSE authenticators are accepted and passed
to rxgk_decrypt_skb(), which can later reach skb_to_sgvec() with an
impossible length and hit BUG_ON(len).

Decoded from the original latest-net reproduction logs with
scripts/decode_stacktrace.sh:

RIP: __skb_to_sgvec()
  [net/core/skbuff.c:5285 (discriminator 1)]
Call Trace:
 skb_to_sgvec() [net/core/skbuff.c:5305]
 rxgk_decrypt_skb() [net/rxrpc/rxgk_common.h:81]
 rxgk_verify_response() [net/rxrpc/rxgk.c:1268]
 rxrpc_process_connection()
   [net/rxrpc/conn_event.c:266 net/rxrpc/conn_event.c:364
    net/rxrpc/conn_event.c:386]
 process_one_work() [kernel/workqueue.c:3281]
 worker_thread()
   [kernel/workqueue.c:3353 kernel/workqueue.c:3440]
 kthread() [kernel/kthread.c:436]
 ret_from_fork() [arch/x86/kernel/process.c:164]

Reject authenticator lengths that exceed the remaining packet payload.

Fixes: 9d1d2b59341f ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)")
Signed-off-by: Keenan Dong <keenanat2000 at gmail.com>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: Simon Horman <horms at kernel.org>
cc: Willy Tarreau <w at 1wt.eu>
cc: linux-afs at lists.infradead.org
cc: stable at kernel.org
Link: https://patch.msgid.link/20260408121252.2249051-14-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 |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -1224,7 +1224,7 @@ static int rxgk_verify_response(struct r
 
 	auth_offset	= offset;
 	auth_len	= ntohl(xauth_len);
-	if (auth_len < len)
+	if (auth_len > len)
 		goto short_packet;
 	if (auth_len & 3)
 		goto inconsistent;