linux-kernel - Re: [PATCH] crypto: drbg - set freed buffers to NULL

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Message-ID: <20180411172923.GA94221@gmail.com>
Date:   Wed, 11 Apr 2018 10:29:23 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Stephan Müller <smueller@...onox.de>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        "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,
        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 - set freed buffers to NULL

On Wed, Apr 11, 2018 at 04:31:01PM +0200, Stephan Müller wrote:
> Sorry, this time with the proper subject line.
> 
> ---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@...onox.de>
> Reported-by: syzbot+75397ee3df5c70164154@...kaller.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;

Can you please add Fixes and Cc stable?

- Eric