linux-kernel - Re: pty: fix use after free/oops at pty_unix98

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Date:	Tue, 15 Dec 2015 14:36:04 -0200
From:	"Herton R. Krzesinski" <herton@...hat.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>
Subject: Re: pty: fix use after free/oops at pty_unix98_shutdown

On Tue, Dec 15, 2015 at 08:17:56AM -0800, Peter Hurley wrote:
> > I also expect in a rare case where all ptmx references are gone/closed, this also
> > could happen on final close when the master tty is given to pty_unix98_shutdown.
> 
> This logic I'm not following. If the pty master is being released, then the inode
> is valid for the release() operation in-progress.

Hi Peter,

yes, you're right if you are eg. closing the /dev/ptmx or /dev/pts/ptmx file
previously opened. But I thought and refer above to the case where for example
you are closing /dev/tty and that's the final close and there is no other
process in the system with the /dev/{,*/}ptmx opened, the inode which referenced
the previously opened ptmx could be gone. It would be rare though since in a
running system any logged in user eg. through ssh or with a terminal open in X
will have at least a ptmx device opened.

> 
> Regards,
> Peter Hurley
>

-- 
[]'s
Herton 
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