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    SubjectRe: [PATCH] dh key: fix rounding up KDF output length
    On Thu, 7 Jun 2018, Kees Cook wrote:

    > On Thu, Jun 7, 2018 at 12:12 PM, Eric Biggers <ebiggers3@gmail.com> 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.
    >
    > round_up() vs roundup(). Wow, that's not confusing. :( I wonder if we
    > should rename the former to roundup_pow2() or something?

    Good idea, in a separate patch(set).

    --
    James Morris
    <jmorris@namei.org>

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