linux-kernel - Re: [PATCH v2 2/2] TTY: ntty, add one more sanity check

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Date:	Tue, 7 Jun 2011 10:10:43 -0700
From:	Greg KH <greg@...ah.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	gregkh@...e.de, jirislaby@...il.com, linux-kernel@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v2 2/2] TTY: ntty, add one more sanity check

On Tue, Jun 07, 2011 at 06:57:50PM +0200, Jiri Slaby wrote:
> On 06/07/2011 06:44 PM, Greg KH wrote:
> > On Sun, Jun 05, 2011 at 02:16:17PM +0200, Jiri Slaby wrote:
> >> With the previous patch, we fixed another bug where read_buf was freed
> >> while we still was in n_tty_read. We currently check whether read_buf
> >> is NULL at the start of the function. Add one more check after we wake
> >> up from waiting for input.
> >>
> >> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> >> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> >> ---
> >>  drivers/tty/n_tty.c |    1 +
> >>  1 files changed, 1 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> >> index 95d0a9c..c62c856 100644
> >> --- a/drivers/tty/n_tty.c
> >> +++ b/drivers/tty/n_tty.c
> >> @@ -1785,6 +1785,7 @@ do_it_again:
> >>  				break;
> >>  			}
> >>  			timeout = schedule_timeout(timeout);
> >> +			BUG_ON(!tty->read_buf);
> > 
> > So, if we ever hit this, what are we going to do with this crash?
> > 
> > I really don't want to add more BUG_ON() calls to the kernel if at all
> > possible.  Or is it the case that we will crash if this case is true
> > soon afterward anyway?
> 
> Yeah, it will crash something like 10 lines below. The pointer is
> dereferenced there.

Ok, fair enough, thanks.

greg k-h
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