[PATCH net v4 13/15] rxrpc: fix RESPONSE authenticator parser OOB read

[David Howells <dhowells@redhat.com>]

From: Keenan Dong <keenanat2000@gmail.com>

rxgk_verify_authenticator() copies auth_len bytes into a temporary
buffer and then passes p + auth_len as the parser limit to
rxgk_do_verify_authenticator(). Since p is a __be32 *, that inflates the
parser end pointer by a factor of four and lets malformed RESPONSE
authenticators read past the kmalloc() buffer.

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

BUG: KASAN: slab-out-of-bounds in rxgk_verify_response()
Call Trace:
 dump_stack_lvl() [lib/dump_stack.c:123]
 print_report() [mm/kasan/report.c:379 mm/kasan/report.c:482]
 kasan_report() [mm/kasan/report.c:597]
 rxgk_verify_response()
   [net/rxrpc/rxgk.c:1103 net/rxrpc/rxgk.c:1167
    net/rxrpc/rxgk.c:1274]
 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]

Allocated by task 54:
 rxgk_verify_response()
   [include/linux/slab.h:954 net/rxrpc/rxgk.c:1155
    net/rxrpc/rxgk.c:1274]
 rxrpc_process_connection()
   [net/rxrpc/conn_event.c:266 net/rxrpc/conn_event.c:364
    net/rxrpc/conn_event.c:386]

Convert the byte count to __be32 units before constructing the parser
limit.

Fixes: 9d1d2b59341f ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)")
Signed-off-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@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: Willy Tarreau <w@1wt.eu>
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 f9f5a2dc62ed..01dbdf0b5cf2 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -1164,7 +1164,8 @@ static int rxgk_verify_authenticator(struct rxrpc_connection *conn,
 	}
 
 	p = auth;
-	ret = rxgk_do_verify_authenticator(conn, krb5, skb, p, p + auth_len);
+	ret = rxgk_do_verify_authenticator(conn, krb5, skb, p,
+					   p + auth_len / sizeof(*p));
 error:
 	kfree(auth);
 	return ret;