Re: [patch] ASoC: soc: snprintf() doesn't return negative

Dan Carpenter
2010-10-11T21:11:38Z

On Mon, Oct 11, 2010 at 09:45:02PM +0200, Dan Carpenter wrote:
> On Mon, Oct 11, 2010 at 07:51:48PM +0100, Mark Brown wrote:
> > In actual fact quite a few devices have enough registers to be
> > truncated, meaning that it's not only possible but likely we'll exercise
> > the cases that deal with the end of buffer. If snprintf() is returning
> > values larger than buffer size it was given we're likely to have an
> > issue but it seems that there's something missing in your analysis since
> > we're never seeing WARN_ON()s and are instead seeing the behaviour the
> > code is intended to give, which is to truncate the output when we run
> > out of space.
> >
> > Could you re-check your analysis, please?
>
> That's odd. I'm sorry, I can't explain why you wouldn't see a stack
> trace... The code is straight forward:
>
> /* Reject out-of-range values early. Large positive sizes are
> used for unknown buffer sizes. */
> if (WARN_ON_ONCE((int) size < 0))
> return 0;
>
> It would still give you truncated output but after the NULL terminator
> there would be information leaked from the kernel. If the reader
> program had allocated a large enough buffer to handle the extra
> information it wouldn't cause a problem.
>

Actually it will never cause a problem with userspace because we pass
the size of the userspace buffer to the kernel. The only issues are the
information leak if the user passes in a 8k buffer and the also the
WARN_ON_ONCE()

regards,
dan carpenter