random: check for increase of entropy_count because of signed conversion

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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.

[ Commit modified by tytso to add an additional safety check for a
  negative entropy_count -- which should never happen, and to also add
  an additional paranoia check to prevent overly large count values to
  be passed into urandom_read().  ]

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

...

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Hannes Frederic Sowa 2014-07-18 17:26:41 -04:00 • committed by Theodore Ts'o

parent 1795cd9b3a

commit 79a8468747

1 changed files with 14 additions and 3 deletions

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drivers/char/random.c

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