linux-kernel - Re: [RFC PATCH v2 3/4] Fix twofish crypto functions prototype casts

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Date:   Mon, 6 May 2019 15:19:55 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joao Moreira <jmoreira@...e.de>
Cc:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH v2 3/4] Fix twofish crypto functions prototype casts

On Mon, May 6, 2019 at 12:20 PM Joao Moreira <jmoreira@...e.de> wrote:
> RFC: twofish_enc_blk_ctr_3way is assigned both to .ecb and to .ctr,
> what makes its declaration through the macro undoable, as thought in
> this patch. Suggestions on how to fix this are welcome.

This looks like a typo in the original code (due to the lack of type checking!)

typedef void (*common_glue_func_t)(void *ctx, u8 *dst, const u8 *src);
...
#define GLUE_FUNC_CAST(fn) ((common_glue_func_t)(fn))
...
void twofish_enc_blk_ctr_3way(void *ctx, u128 *dst, const u128 *src,
                             le128 *iv)

static const struct common_glue_ctx twofish_ctr = {
...
               .fn_u = { .ecb = GLUE_FUNC_CAST(twofish_enc_blk_ctr_3way) }
...
        return glue_ctr_req_128bit(&twofish_ctr, req);

int glue_ctr_req_128bit(const struct common_glue_ctx *gctx,
                        struct skcipher_request *req)
...
                                gctx->funcs[i].fn_u.ctr(ctx, dst, src, &ctrblk);

The twofish_ctr structure is actually only ever using the .ctr
assignment in the code, but it's a union, so the assignment via .ecb
is the same as .ctr.

-- 
Kees Cook