random: make 'add_interrupt_randomness()' do something sane
authorTheodore Ts'o <tytso@mit.edu>
Mon, 2 Jul 2012 11:52:16 +0000 (07:52 -0400)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 15 Aug 2012 15:10:10 +0000 (08:10 -0700)
commit0110bbfbc8ed1b5240a51e8c767c44a856424139
treef3ac162b4925c7e841413db59dabff88324640ae
parentcabf5b0af54cec6a2f9ce674cbc96fc8aa2fc468
random: make 'add_interrupt_randomness()' do something sane

commit 775f4b297b780601e61787b766f306ed3e1d23eb upstream.

We've been moving away from add_interrupt_randomness() for various
reasons: it's too expensive to do on every interrupt, and flooding the
CPU with interrupts could theoretically cause bogus floods of entropy
from a somewhat externally controllable source.

This solves both problems by limiting the actual randomness addition
to just once a second or after 64 interrupts, whicever comes first.
During that time, the interrupt cycle data is buffered up in a per-cpu
pool.  Also, we make sure the the nonblocking pool used by urandom is
initialized before we start feeding the normal input pool.  This
assures that /dev/urandom is returning unpredictable data as soon as
possible.

(Based on an original patch by Linus, but significantly modified by
tytso.)

Tested-by: Eric Wustrow <ewust@umich.edu>
Reported-by: Eric Wustrow <ewust@umich.edu>
Reported-by: Nadia Heninger <nadiah@cs.ucsd.edu>
Reported-by: Zakir Durumeric <zakir@umich.edu>
Reported-by: J. Alex Halderman <jhalderm@umich.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/char/random.c
drivers/mfd/ab3100-core.c
include/linux/random.h
kernel/irq/handle.c