linux-kernel - [PATCH] net: hso: fix NULL-deref on disconnect regression

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Message-Id: <20210426081149.10498-1-johan@kernel.org>
Date:   Mon, 26 Apr 2021 10:11:49 +0200
From:   Johan Hovold <johan@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>,
        stable@...r.kernel.org, Anirudh Rayabharam <mail@...rudhrb.com>,
        Leonardo Antoniazzi <leoanto@...ba.it>
Subject: [PATCH] net: hso: fix NULL-deref on disconnect regression

Commit 8a12f8836145 ("net: hso: fix null-ptr-deref during tty device
unregistration") fixed the racy minor allocation reported by syzbot, but
introduced an unconditional NULL-pointer dereference on every disconnect
instead.

Specifically, the serial device table must no longer be accessed after
the minor has been released by hso_serial_tty_unregister().

Fixes: 8a12f8836145 ("net: hso: fix null-ptr-deref during tty device unregistration")
Cc: stable@...r.kernel.org
Cc: Anirudh Rayabharam <mail@...rudhrb.com>
Reported-by: Leonardo Antoniazzi <leoanto@...ba.it>
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/net/usb/hso.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index 9bc58e64b5b7..3ef4b2841402 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -3104,7 +3104,7 @@ static void hso_free_interface(struct usb_interface *interface)
 			cancel_work_sync(&serial_table[i]->async_put_intf);
 			cancel_work_sync(&serial_table[i]->async_get_intf);
 			hso_serial_tty_unregister(serial);
-			kref_put(&serial_table[i]->ref, hso_serial_ref_free);
+			kref_put(&serial->parent->ref, hso_serial_ref_free);
 		}
 	}
 
-- 
2.26.3