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crypto: hash - Fix the pointer voodoo in unaligned ahash

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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: Marek 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: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Marek Vasut 2014-03-14 02:37:04 +01:00 committed by Herbert Xu
parent 85e0da925b
commit ab6bf4e5e5
1 changed files with 49 additions and 7 deletions
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56
crypto/ahash.c
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@ -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;
/*
* 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" .
*/
/* First copy areq->result into areq->priv.result */
ahash_op_unaligned_finish(areq, err);
areq->base.complete = complete;
areq->base.data = data;
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;