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Message-ID: <20170616083111.5cwwkzyauocxafou@breakpoint.cc>
Date: Fri, 16 Jun 2017 10:31:12 +0200
From: Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: Theodore Ts'o <tytso@....edu>,
Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
kernel-hardening@...ts.openwall.com,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Eric Biggers <ebiggers3@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
David Miller <davem@...emloft.net>, tglx@...utronix.de
Subject: Re: [PATCH v5 01/13] random: invalidate batched entropy after crng
init
On 2017-06-15 00:33:12 [+0200], Jason A. Donenfeld wrote:
> There's a potential race that I fixed in my v5 of that patch set, but
> Ted only took v4, and for whatever reason has been to busy to submit
> the additional patch I already posted showing the diff between v4&v5.
> Hopefully he actually gets around to it and sends this for the next
> rc. Here it is:
>
> https://patchwork.kernel.org/patch/9774563/
So you replace "crng_init < 2" with use_lock instead. That is not what I
am talking about. Again:
add_interrupt_randomness()
-> crng_fast_load() spin_trylock_irqsave(&primary_crng.lock, )
-> invalidate_batched_entropy() write_lock_irqsave(&batched_entropy_reset_lock, );
in that order while the code path
get_random_uXX() read_lock_irqsave(&batched_entropy_reset_lock, );
-> extract_crng()
-> _extract_crng() spin_lock_irqsave(&crng->lock, );
which allocates the same lock in opposite order.
That means
T1 T2
crng_fast_load() get_random_u64()
extract_crng()
*dead lock*
invalidate_batched_entropy()
_extract_crng()
So T1 waits for batched_entropy_reset_lock holding primary_crng.lock and
T2 waits for primary_crng.lock holding batched_entropy_reset_lock.
Sebastian
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