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Subject: Re: [PATCH] tty: serial_core: Fix uart_state leak when port shutdown
To:     Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     yuanxzhang@fudan.edu.cn, kjlu@umn.edu,
        Xin Tan <tanxin.ctf@gmail.com>
References: <1592052665-95042-1-git-send-email-xiyuyang19@fudan.edu.cn>
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Date:   Mon, 15 Jun 2020 06:56:11 +0200
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On 13. 06. 20, 14:51, Xiyu Yang wrote:
> uart_shutdown() invokes uart_port_lock(), which returns a reference of
> the uart_port object if increases the refcount of the uart_state object
> successfully or returns NULL if fails.
> 
> However, uart_shutdown() don't take the return value of uart_port_lock()
> as the new uart_port object to "uport" and use the old "uport" instead
> to balance refcount in uart_port_unlock(), which may cause a redundant
> decrement of refcount occurred when the new "uport" equals to NULL and
> then cause a potential memory leak.

uport should be valid at that point and both the returned one and the
used one should be the same.

> Fix this issue by update the "uport" object to the return value of
> uart_port_lock() when invoking uart_port_lock().

Do you actually encounter the issue or is this some static analyzer result?

> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  drivers/tty/serial/serial_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 57840cf90388..ab8756ef2b60 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -313,7 +313,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
>  	 * console driver may need to allocate/free a debug object, which
>  	 * can endup in printk() recursion.
>  	 */
> -	uart_port_lock(state, flags);
> +	uport = uart_port_lock(state, flags);
>  	xmit_buf = state->xmit.buf;
>  	state->xmit.buf = NULL;
>  	uart_port_unlock(uport, flags);
> 

thanks,
-- 
js
suse labs