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

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Date:	Tue, 07 Jun 2011 18:57:50 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Greg KH <greg@...ah.com>
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 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.

thanks,
-- 
js
suse labs
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