Re: [PATCH] tty: Correct tty buffer flush.

Ben Hutchings
2013-03-17T04:06:46Z

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On Mon, 2013-03-04 at 23:19 +0400, Ilya Zykov wrote:
> On 03.12.2012 13:54, Ilya Zykov wrote:
> > The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
> > when another thread can use it. It can be cause of "NULL pointer dereference".
> > Main idea of the patch, this is never release last (struct tty_buffer) in the active buffer.
> > Only flush data for ldisc(tty->buf.head->read = tty->buf.head->commit).
> > At that moment driver can collect(write) data in buffer without conflict.
> > It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.
> > Test program and bug report you can see:
> > https://lkml.org/lkml/2012/11/29/368
> >
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
> > ---
> > diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> > index 6c9b7cd..4f02f9c 100644
> > --- a/drivers/tty/tty_buffer.c
> > +++ b/drivers/tty/tty_buffer.c
> > @@ -114,11 +114,14 @@ static void __tty_buffer_flush(struct tty_struct *tty)
> > {
> > struct tty_buffer *thead;
> >
> > - while ((thead = tty->buf.head) != NULL) {
> > - tty->buf.head = thead->next;
> > - tty_buffer_free(tty, thead);
> > + if (tty->buf.head == NULL)
> > + return;
> > + while ((thead = tty->buf.head->next) != NULL) {
> > + tty_buffer_free(tty, tty->buf.head);
> > + tty->buf.head = thead;
> > }
> > - tty->buf.tail = NULL;
> > + WARN_ON(tty->buf.head != tty->buf.tail);
> > + tty->buf.head->read = tty->buf.head->commit;
> > }
> >
> > /**
> >
>
> You can include this patch, in 3.2 series , for improve stability,
> it would be merged in upstream 3.9-rc1.

Added to the queue, thanks.

Ben.

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Ben Hutchings
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