linux-kernel - Re: [PATCH] tty: serial_core: Fix uart_state refcnt leak when the port startup

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Date:   Sat, 27 Jun 2020 13:43:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Xiyu Yang <xiyuyang19@...an.edu.cn>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, yuanxzhang@...an.edu.cn,
        kjlu@....edu, Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH] tty: serial_core: Fix uart_state refcnt leak when the
 port startup

On Wed, Jun 24, 2020 at 11:42:59AM +0200, Jiri Slaby wrote:
> On 24. 06. 20, 11:34, Greg Kroah-Hartman wrote:
> > On Sat, Jun 13, 2020 at 08:52:18PM +0800, Xiyu Yang wrote:
> >> uart_port_startup() 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_port_startup() 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.
> >>
> >> Fix this issue by update the "uport" object to the return value of
> >> uart_port_lock() when invoking uart_port_lock().
> >>
> >> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> >> Signed-off-by: Xin Tan <tanxin.ctf@...il.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..968fd619aec0 100644
> >> --- a/drivers/tty/serial/serial_core.c
> >> +++ b/drivers/tty/serial/serial_core.c
> >> @@ -205,7 +205,7 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
> >>  	if (!page)
> >>  		return -ENOMEM;
> >>  
> >> -	uart_port_lock(state, flags);
> >> +	uport = uart_port_lock(state, flags);
> > 
> > How is this a different pointer than you originally had?
> 
> Was this patch sent twice? As I had very same questions on the other
> one, but never received a feedback:
> https://lore.kernel.org/linux-serial/bf6c1e7b-3dc6-aba6-955a-fee351a6d800@suse.com/
> 
> 
> Oh, wait: this is uart_port_startup, I commented on the uart_shutdown
> one. But whatever, I would scratch both of them.

Yeah, you are right, dropping them both now, thanks.

greg k-h