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.
regards,
dan carpenter
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