Re: [RFC 01/10] crypto: factor async completion for general use

[Eric Biggers]

On Thu, May 11, 2017 at 10:29:47AM +0300, Gilad Ben-Yossef wrote:
> > With regards to the wait being uninterruptible, I agree that this should be the
> > default behavior, because I think users waiting for specific crypto requests are
> > generally not prepared to handle the wait actually being interrupted.  After
> > interruption the crypto operation will still proceed in the background, and it
> > will use buffers which the caller has in many cases already freed.  However, I'd
> > suggest taking a close look at anything that was actually doing an interruptible
> > wait before, to see whether it was a bug or intentional (or "doesn't matter").
> >
> > And yes there could always be a crypto_wait_req_interruptible() introduced if
> > some users need it.
> 
> So this one was a bit of a shocker.  I though the  _interruptible use
> sites seemed
> wrong in the sense of being needless. However, after reading your feedback and
> reviewing the code I'm pretty sure every single one of them (including
> the one I've
> added in dm-verity-target.c this merge window)  are down right dangerous and
> can cause random data corruption... so thanks for pointing this out!
> 
> I though of this patch set as a "make the code pretty" for 4.13 kind
> of patch set.
> Looks like it's a bug fix now, maybe even stable material.
> 
> Anyway, I'll roll a v2 and we'll see.
> 

Any that are called only by kernel threads would theoretically be safe since
kernel threads don't ordinarily receive signals.  But I think that at least the
drbg and gcm waits can be reached by user threads, since they can be called via
algif_rng and algif_aead respectively.

I recommend putting any important fixes first, so they can be backported without
depending on crypto_wait_req().

Eric