Re: [PATCH AUTOSEL 4.4 50/56] tty: pty: Fix race condition between release_one_tty and pty_write

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Jun 01, 2019 at 09:17:07AM -0700, Greg Kroah-Hartman wrote:
> On Sat, Jun 01, 2019 at 09:25:54AM -0400, Sasha Levin wrote:
> > From: Sahara <keun-o.park@darkmatter.ae>
> > 
> > [ Upstream commit b9ca5f8560af244489b4a1bc1ae88b341f24bc95 ]
> > 
> > Especially when a linked tty is used such as pty, the linked tty
> > port's buf works have not been cancelled while master tty port's
> > buf work has been cancelled. Since release_one_tty and flush_to_ldisc
> > run in workqueue threads separately, when pty_cleanup happens and
> > link tty port is freed, flush_to_ldisc tries to access freed port
> > and port->itty, eventually it causes a panic.
> > This patch utilizes the magic value with holding the tty_mutex to
> > check if the tty->link is valid.
> > 
> > Fixes: 2b022ab7542d ("pty: cancel pty slave port buf's work in tty_release")
> > Signed-off-by: Sahara <keun-o.park@darkmatter.ae>
> > Cc: stable <stable@vger.kernel.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> >  drivers/tty/pty.c    | 7 +++++++
> >  drivers/tty/tty_io.c | 3 +++
> >  2 files changed, 10 insertions(+)
> 
> For some reason I did not apply this to the stable kernels, and this
> shouldn't only be for 4.4.y, so please drop this.

Ah, I never applied it because it was later reverted, also upstream,
0eae4686a128 ("Revert "tty: pty: Fix race condition between
release_one_tty and pty_write""), so I didn't apply both of them to the
stable trees as that wouldn't have made sense.

thanks,

greg k-h