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Date:   Wed, 3 Jul 2019 13:31:29 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
Cc:     Herbert Xu <herbert@gondor.apana.org.au>,
        linux-crypto@vger.kernel.org, chetjain@in.ibm.com,
        "David S . Miller" <davem@davemloft.net>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Steffen Klassert <steffen.klassert@secunet.com>
Subject: Re: [PATCH] crypto: user - prevent operating on larval algorithms
Message-ID: <20190703203128.GC10080@gmail.com>
References: <20190701153154.1569c2dc@kitsune.suse.cz>
 <20190702211700.16526-1-ebiggers@kernel.org>
 <20190703143057.miqgc7blhjjxjmee@gondor.apana.org.au>
 <20190703222108.467ec204@kitsune.suse.cz>
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Hi Michal,

On Wed, Jul 03, 2019 at 10:21:08PM +0200, Michal Such?nek wrote:
> On Wed, 3 Jul 2019 22:30:57 +0800
> Herbert Xu <herbert@gondor.apana.org.au> wrote:
> 
> > On Tue, Jul 02, 2019 at 02:17:00PM -0700, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@google.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?
> 

It reproduced pretty reliably for me with what you suggested.  Just typing in
terminal:

	while true; do pcrypt_aead01; done

and then holding Ctrl-C.

If I have time I'll try writing an LTP test that specifically reproduces it.
Yes, it would involve sending a signal to a thread or process that's executing
CRYPTO_MSG_NEWALG (unless I find a better way).

- Eric