Messages in this thread | | | Date | Fri, 18 Jul 2014 17:25:04 -0400 | From | Theodore Ts'o <> | Subject | Re: [PATCH] random: check for increase of entropy_count because of signed conversion |
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On Wed, Jul 16, 2014 at 09:18:15PM +0200, Hannes Frederic Sowa wrote: > The expression entropy_count -= ibytes << (ENTROPY_SHIFT + 3) could > actually increase entropy_count if during assignment of the unsigned > expression on the RHS (mind the -=) we reduce the value modulo > 2^width(int) and assign it to entropy_count. Trinity found this. > > Reported-by: Dave Jones <davej@redhat.com> > Cc: Theodore Ts'o <tytso@mit.edu> > Cc: Greg Price <price@mit.edu> > Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> > --- > As indicated by credit_entropy_bits entropy_count cannot get negative, > so I don't see any reason to include a check for entropy_count < 0 > here. Do you agree?
No, the check is important; after we subtract ibytes << (ENTROPY_SHIFT + 3) we could drive entropy_count negative, and we don't want to trigger the WARN_ON().
I'll modify the patch to keep the check.
- Ted
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