linux-kernel - Re: BUG: NULL pointer deref in tty port / uart

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Message-ID: <20110518144429.GC2011@jolsa.brq.redhat.com>
Date:	Wed, 18 May 2011 16:44:29 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Arnd Bergmann <arnd@...db.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG: NULL pointer deref in tty port / uart

On Wed, May 18, 2011 at 03:36:36PM +0100, Alan Cox wrote:
> > have the same issue.. looks like we should not NULL the port->tty
> > if there's blocked open, but not sure what's exactly the logic
> > behind "port's block_open and count" ..
> 
> A pending open is not a user of the tty as far as the rest of the stack
> is concerned. I also don't see why clearing port->tty is causing this
> crash because nothing on that path should ever be going via port->tty and
> it isn't safe to do so.
> 
> > attached patch fixes it for me
> 
> But still breaks on hangup where we can't do that.
> 
> Where is port->tty getting misused to cause the crash, that is the bit
> I'm missing somewhere.

I think it's the 

uart_update_termios in uart_dtr_rts (drivers/tty/serial/serial_core.c)

called path:

tty_port_block_til_ready
	tty_port_raise_dtr_rts
		uart_dtr_rts
			uart_update_termios

jirka
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