linux-kernel - Re: [PATCH] dh key: fix rounding up KDF output length

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Message-ID: <20180625171426.GA180889@gmail.com>
Date:   Mon, 25 Jun 2018 10:14:26 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     James Morris <jmorris@...ei.org>, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, Tycho Andersen <tycho@...ho.ws>,
        Kees Cook <keescook@...omium.org>,
        Stephan Mueller <smueller@...onox.de>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] dh key: fix rounding up KDF output length

Hi David,

On Fri, Jun 08, 2018 at 04:37:58PM +0100, David Howells wrote:
> Eric Biggers <ebiggers3@...il.com> wrote:
> 
> > Commit 383203eff718 ("dh key: get rid of stack allocated array") changed
> > kdf_ctr() to assume that the length of key material to derive is a
> > multiple of the digest size.  The length was supposed to be rounded up
> > accordingly.  However, the round_up() macro was used which only gives
> > the correct result on power-of-2 arguments, whereas not all hash
> > algorithms have power-of-2 digest sizes.  In some cases this resulted in
> > a write past the end of the 'outbuf' buffer.
> > 
> > Fix it by switching to roundup(), which works for non-power-of-2 inputs.
> 
> Applied.

Applied to where?  When are you planning to send this to Linus?  Note that this
was a regression from v4.17 to v4.18-rc1.

Thanks,

- Eric