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

From: Stephan Mueller <smueller@chronox.de>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>,
	Matthew Wilcox <willy@infradead.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	David Miller <davem@davemloft.net>,
	linux-crypto@vger.kernel.org, Eric Biggers <ebiggers3@gmail.com>,
	syzbot <syzbot+75397ee3df5c70164154@syzkaller.appspotmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] crypto: DRBG - guard uninstantion by lock
Date: Tue, 10 Apr 2018 17:35:29 +0200	[thread overview]
Message-ID: <2704286.80iLvC0rRL@tauon.chronox.de> (raw)
In-Reply-To: <CACT4Y+Y+ydyBAL=j2QOWaBnpY8+Bsr_80d80RXth0SwuY0wMuQ@mail.gmail.com>

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