linux-kernel - Re: [PATCH] crypto: DRBG - guard uninstantion by lock

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Message-ID: <2704286.80iLvC0rRL@tauon.chronox.de>
Date:   Tue, 10 Apr 2018 17:35:29 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, Eric Biggers <ebiggers3@...il.com>,
        syzbot <syzbot+75397ee3df5c70164154@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] crypto: DRBG - guard uninstantion by lock

Am Dienstag, 10. April 2018, 17:23:46 CEST schrieb Dmitry Vyukov:

Hi Dmitry,

> Stephan,
> 
> Do you have any hypothesis as to why this is not detected by KASAN and
> causes silent corruptions?
> We generally try to understand such cases and improve KASAN so that it
> catches such cases more reliably and they do not cause splashes of
> random crashes on syzbot.

I do not have any hypothesis at this point. I know that you induce some fault. 
As you mentioned the drbg_kcapi_seed function, I was looking through the error 
code paths to see whether some error handlers trip over each other. But all is 
guesswork so far. And I am not even sure whether the bug is in the DRBG code 
base.

Looking into the trace you sent, I see a NULL pointer dereference. At one 
point there is also the drbg_init_hash_kernel that is called. But nowhere I 
see any smoking gun.

Could you please give me a description of the fault you are inducing?

Ciao
Stephan