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Commit ab6bf4e5 authored by Marek Vasut's avatar Marek Vasut Committed by Herbert Xu
Browse files

crypto: hash - Fix the pointer voodoo in unaligned ahash 



Add documentation for the pointer voodoo that is happening in crypto/ahash.c
in ahash_op_unaligned(). This code is quite confusing, so add a beefy chunk
of documentation.

Moreover, make sure the mangled request is completely restored after finishing
this unaligned operation. This means restoring all of .result, .base.data
and .base.complete .

Also, remove the crypto_completion_t complete = ... line present in the
ahash_op_unaligned_done() function. This type actually declares a function
pointer, which is very confusing.

Finally, yet very important nonetheless, make sure the req->priv is free()'d
only after the original request is restored in ahash_op_unaligned_done().
The req->priv data must not be free()'d before that in ahash_op_unaligned_finish(),
since we would be accessing previously free()'d data in ahash_op_unaligned_done()
and cause corruption.

Signed-off-by: default avatarMarek Vasut <marex@denx.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 85e0da92

crypto/ahash.c

+49 −7
Original line number Diff line number Diff line
@@ -201,22 +201,34 @@ static void ahash_op_unaligned_finish(struct ahash_request *req, int err) 
		memcpy(priv->result, req->result,

		       crypto_ahash_digestsize(crypto_ahash_reqtfm(req)));



	/* Restore the original crypto request. */

	req->result = priv->result;

	req->base.complete = priv->complete;

	req->base.data = priv->data;

	req->priv = NULL;



	/* Free the req->priv.priv from the ADJUSTED request. */

	kzfree(priv);

}



static void ahash_op_unaligned_done(struct crypto_async_request *req, int err)

{

	struct ahash_request *areq = req->data;

	struct ahash_request_priv *priv = areq->priv;

	crypto_completion_t complete = priv->complete;

	void *data = priv->data;



	ahash_op_unaligned_finish(areq, err);

	/*

	 * Restore the original request, see ahash_op_unaligned() for what

	 * goes where.

	 *

	 * The "struct ahash_request *req" here is in fact the "req.base"

	 * from the ADJUSTED request from ahash_op_unaligned(), thus as it

	 * is a pointer to self, it is also the ADJUSTED "req" .

	 */



	areq->base.complete = complete;

	areq->base.data = data;

	/* First copy areq->result into areq->priv.result */

	ahash_op_unaligned_finish(areq, err);



	complete(&areq->base, err);

	/* Complete the ORIGINAL request. */

	areq->base.complete(&areq->base, err);

}



static int ahash_op_unaligned(struct ahash_request *req,
@@ -234,9 +246,39 @@ static int ahash_op_unaligned(struct ahash_request *req, 
	if (!priv)

		return -ENOMEM;



	/*

	 * WARNING: Voodoo programming below!

	 *

	 * The code below is obscure and hard to understand, thus explanation

	 * is necessary. See include/crypto/hash.h and include/linux/crypto.h

	 * to understand the layout of structures used here!

	 *

	 * The code here will replace portions of the ORIGINAL request with

	 * pointers to new code and buffers so the hashing operation can store

	 * the result in aligned buffer. We will call the modified request

	 * an ADJUSTED request.

	 *

	 * The newly mangled request will look as such:

	 *

	 * req {

	 *   .result        = ADJUSTED[new aligned buffer]

	 *   .base.complete = ADJUSTED[pointer to completion function]

	 *   .base.data     = ADJUSTED[*req (pointer to self)]

	 *   .priv          = ADJUSTED[new priv] {

	 *           .result   = ORIGINAL(result)

	 *           .complete = ORIGINAL(base.complete)

	 *           .data     = ORIGINAL(base.data)

	 *   }

	 */



	priv->result = req->result;

	priv->complete = req->base.complete;

	priv->data = req->base.data;

	/*

	 * WARNING: We do not backup req->priv here! The req->priv

	 *          is for internal use of the Crypto API and the

	 *          user must _NOT_ _EVER_ depend on it's content!

	 */



	req->result = PTR_ALIGN((u8 *)priv->ubuf, alignmask + 1);

	req->base.complete = ahash_op_unaligned_done;