Re: [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@xxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+29d17b7898b41ee120a5@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+8a608baf8751184ec727@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+d04e58bd384f1fe0b112@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 383203eff718 ("dh key: get rid of stack allocated array")
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>

Arg, thanks.

Acked-by: Tycho Andersen <tycho@xxxxxxxx>