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

From: David Howells
Date: Fri Jun 08 2018 - 11:38:13 EST

Eric Biggers <ebiggers3@xxxxxxxxx> 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.