[PATCH] dh key: fix rounding up KDF output length

[Tycho Andersen]

On Thu, Jun 07, 2018 at 12:12:01PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers at 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 at syzkaller.appspotmail.com
> Reported-by: syzbot+29d17b7898b41ee120a5 at syzkaller.appspotmail.com
> Reported-by: syzbot+8a608baf8751184ec727 at syzkaller.appspotmail.com
> Reported-by: syzbot+d04e58bd384f1fe0b112 at syzkaller.appspotmail.com
> Fixes: 383203eff718 ("dh key: get rid of stack allocated array")
> Signed-off-by: Eric Biggers <ebiggers at google.com>

Arg, thanks.

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