From: Dmitry Vyukov <dvyukov@google.com>
To: "Stephan Müller" <smueller@chronox.de>
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: Wed, 11 Apr 2018 19:09:53 +0200 [thread overview]
Message-ID: <CACT4Y+ZxumagMiZTFwzX2e_tdd4U862BzgzHVDsiOACbMXEh_A@mail.gmail.com> (raw)
In-Reply-To: <2186798.qrgUIDAn9S@positron.chronox.de>
On Wed, Apr 11, 2018 at 4:26 PM, Stephan Müller <smueller@chronox.de> wrote:
> Hi Dimitry,
>
> This fix prevents the kernel from crashing when injecting the fault.
Good!
> Stack traces are yet shown but I guess that is expected every time
> a fault is injected.
Yes, nothing to fix here.
> As to why KASAN did not notice this one, I am not sure. Maybe it is
> because I use two buffer pointers to point to (almost) the same memory
> (one that is aligned and one pointing to the complete buffer)?
After looking at the fix, I figured out what happened with KASAN.
Filed https://bugzilla.kernel.org/show_bug.cgi?id=199359. In short,
tricky interplay between kzfree, ksize and double-free detection.
If KASAN worked as intended it would give a nice "double-free in this
stack for object allocated in this stack and previously freed in this
stack", which would probably make debugging much simpler.
> ---8<---
>
> During freeing of the internal buffers used by the DRBG, set the pointer
> to NULL. It is possible that the context with the freed buffers is
> reused. In case of an error during initialization where the pointers
> do not yet point to allocated memory, the NULL value prevents a double
> free.
>
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> Reported-by: syzbot+75397ee3df5c70164154@syzkaller.appspotmail.com
> ---
> crypto/drbg.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/crypto/drbg.c b/crypto/drbg.c
> index 4faa2781c964..466a112a4446 100644
> --- a/crypto/drbg.c
> +++ b/crypto/drbg.c
> @@ -1134,8 +1134,10 @@ static inline void drbg_dealloc_state(struct drbg_state *drbg)
> if (!drbg)
> return;
> kzfree(drbg->Vbuf);
> + drbg->Vbuf = NULL;
> drbg->V = NULL;
> kzfree(drbg->Cbuf);
> + drbg->Cbuf = NULL;
> drbg->C = NULL;
> kzfree(drbg->scratchpadbuf);
> drbg->scratchpadbuf = NULL;
> --
> 2.14.3
>
>
>
>
> --
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prev parent reply other threads:[~2018-04-11 17:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-06 13:24 WARNING in kmem_cache_free syzbot
2018-04-06 13:33 ` Dmitry Vyukov
2018-04-08 3:16 ` Use struct page for filename Matthew Wilcox
2018-04-08 4:42 ` Al Viro
2018-04-08 5:59 ` WARNING in kmem_cache_free Al Viro
2018-04-08 6:01 ` Matthew Wilcox
2018-04-08 10:26 ` Dmitry Vyukov
2018-04-08 11:18 ` Dmitry Vyukov
2018-04-08 15:31 ` Stephan Müller
2018-04-08 15:41 ` Dmitry Vyukov
2018-04-08 19:07 ` [PATCH] crypto: DRBG - guard uninstantion by lock Stephan Müller
2018-04-08 22:46 ` Theodore Y. Ts'o
2018-04-09 5:40 ` Stephan Mueller
2018-04-09 7:57 ` Dmitry Vyukov
2018-04-10 15:23 ` Dmitry Vyukov
2018-04-10 15:35 ` Stephan Mueller
2018-04-11 12:29 ` Dmitry Vyukov
2018-04-11 12:59 ` Stephan Mueller
2018-04-11 14:26 ` Stephan Müller
2018-04-11 14:31 ` [PATCH] crypto: drbg - set freed buffers to NULL Stephan Müller
2018-04-11 17:29 ` Eric Biggers
2018-04-12 6:40 ` Stephan Müller
2018-04-20 16:54 ` Herbert Xu
2018-04-11 17:09 ` Dmitry Vyukov [this message]
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