linux-kernel - Re: [PATCH] usb: gadget: u_serial: Add null pointer checks after RX/TX submission

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Message-ID: <02bec7b8-7754-4b9d-84ae-51621d6aa7ec@kernel.org>
Date: Thu, 18 Jan 2024 10:27:54 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Kuen-Han Tsai <khtsai@...gle.com>, gregkh@...uxfoundation.org,
 quic_prashk@...cinc.com, stern@...land.harvard.edu,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: u_serial: Add null pointer checks after
 RX/TX submission

On 16. 01. 24, 15:16, Kuen-Han Tsai wrote:
> Commit ffd603f21423 ("usb: gadget: u_serial: Add null pointer check in
> gs_start_io") adds null pointer checks to gs_start_io(), but it doesn't
> fully fix the potential null pointer dereference issue. While
> gserial_connect() calls gs_start_io() with port_lock held, gs_start_rx()
> and gs_start_tx() release the lock during endpoint request submission.
> This creates a window where gs_close() could set port->port_tty to NULL,
> leading to a dereference when the lock is reacquired.
> 
> This patch adds a null pointer check for port->port_tty after RX/TX
> submission, and removes the initial null pointer check in gs_start_io()
> since the caller must hold port_lock and guarantee non-null values for
> port_usb and port_tty.

Or you switch to tty_port refcounting and need not fiddling with this at 
all ;).

thanks,
-- 
js
suse labs