linux-kernel - Re: [PATCH] crypto: user - prevent operating on larval algorithms

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Date:   Wed, 3 Jul 2019 22:21:08 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-crypto@...r.kernel.org,
        chetjain@...ibm.com, "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH] crypto: user - prevent operating on larval algorithms

On Wed, 3 Jul 2019 22:30:57 +0800
Herbert Xu <herbert@...dor.apana.org.au> wrote:

> On Tue, Jul 02, 2019 at 02:17:00PM -0700, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > Michal Suchanek reported [1] that running the pcrypt_aead01 test from
> > LTP [2] in a loop and holding Ctrl-C causes a NULL dereference of
> > alg->cra_users.next in crypto_remove_spawns(), via crypto_del_alg().
> > The test repeatedly uses CRYPTO_MSG_NEWALG and CRYPTO_MSG_DELALG.
> > 
> > The crash occurs when the instance that CRYPTO_MSG_DELALG is trying to
> > unregister isn't a real registered algorithm, but rather is a "test
> > larval", which is a special "algorithm" added to the algorithms list
> > while the real algorithm is still being tested.  Larvals don't have
> > initialized cra_users, so that causes the crash.  Normally pcrypt_aead01
> > doesn't trigger this because CRYPTO_MSG_NEWALG waits for the algorithm
> > to be tested; however, CRYPTO_MSG_NEWALG returns early when interrupted.
> > 

Do you have some way to reproduce this reliably?

I suppose you would have to send a signal to the process for the call
to get interrupted, right?

Thanks

Michal