Messages in this thread | | | Date | Thu, 27 Mar 2014 10:04:03 +0100 | From | Daniel Borkmann <> | Subject | Re: [PATCH] random32: avoid attempt to late reseed if in the middle of seeding |
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On 03/27/2014 03:21 AM, Hannes Frederic Sowa wrote: > On Wed, Mar 26, 2014 at 07:35:01PM -0400, Sasha Levin wrote: >> On 03/26/2014 07:18 PM, Daniel Borkmann wrote: >>> On 03/26/2014 06:12 PM, Sasha Levin wrote: >>>> Commit 4af712e8df ("random32: add prandom_reseed_late() and call when >>>> nonblocking pool becomes initialized") has added a late reseed stage >>>> that happens as soon as the nonblocking pool is marked as initialized. >>>> >>>> This fails in the case that the nonblocking pool gets initialized >>>> during __prandom_reseed()'s call to get_random_bytes(). In that case >>>> we'd double back into __prandom_reseed() in an attempt to do a late >>>> reseed - deadlocking on 'lock' early on in the boot process. >>>> >>>> Instead, just avoid even waiting to do a reseed if a reseed is already >>>> occuring. >>>> >>>> Signed-off-by: Sasha Levin <sasha.levin@oracle.com> >>> >>> Thanks for catching! (If you want Dave to pick it up, please also >>> Cc netdev.) >>> >>> Why not via spin_trylock_irqsave() ? Thus, if we already hold the >>> lock, we do not bother any longer with doing the same work twice >>> and just return. > > I totally agree with Daniel spin_trylock_irqsave seems like the best > solution. > > In case we really want to make sure that even early seeding doesn't > race with late seed and the pool is only filled by another CPU, we would > actually need per-cpu bools to get this case correct.
But then again, we would just exit via spin_trylock_irqsave() now, no? Whenever something enters this section protected under irq save spinlock we would do a reseed of the entire state (s1-s4) for each cpu.
>> Your code looks much better, I'll should really stop sending patches >> too early in the morning... >> >> It's also worth adding lib/random32.c to the MAINTAINERS file, as my >> list of recipients is solely based on what get_maintainer.pl tells >> me to do (and I'm assuming that I'm not the last person who will be >> sending patches for this). > > Would be a nice idea, especially because prandom_u32 changes are sensitive to > network security and should get reviewed there, too.
Indeed, sounds good to me.
> Greetings, > > Hannes >
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