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

From: Kees Cook
Date: Mon May 06 2019 - 18:21:25 EST

On Mon, May 6, 2019 at 12:20 PM Joao Moreira <jmoreira@xxxxxxx> 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