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Date:   Thu, 7 Jun 2018 14:28:31 -0600
From:   Tycho Andersen <tycho@tycho.ws>
To:     Eric Biggers <ebiggers3@gmail.com>
Cc:     David Howells <dhowells@redhat.com>,
        James Morris <jmorris@namei.org>, keyrings@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com, Kees Cook <keescook@chromium.org>,
        Stephan Mueller <smueller@chronox.de>,
        Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH] dh key: fix rounding up KDF output length
Message-ID: <20180607202831.GG9999@cisco>
References: <0000000000009c221d056e0cf53a@google.com>
 <20180607191201.97080-1-ebiggers3@gmail.com>
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On Thu, Jun 07, 2018 at 12:12:01PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> 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.
> 
> Reported-by: syzbot+486f97f892efeb2075a3@syzkaller.appspotmail.com
> Reported-by: syzbot+29d17b7898b41ee120a5@syzkaller.appspotmail.com
> Reported-by: syzbot+8a608baf8751184ec727@syzkaller.appspotmail.com
> Reported-by: syzbot+d04e58bd384f1fe0b112@syzkaller.appspotmail.com
> Fixes: 383203eff718 ("dh key: get rid of stack allocated array")
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Arg, thanks.

Acked-by: Tycho Andersen <tycho@tycho.ws>