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, .priv, .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@xxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Shawn Guo <shawn.guo@xxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
crypto/ahash.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 54 insertions(+), 11 deletions(-)
diff --git a/crypto/ahash.c b/crypto/ahash.c
index a92dc38..5ca8ede 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -29,6 +29,7 @@
struct ahash_request_priv {
crypto_completion_t complete;
void *data;
+ void *priv;
u8 *result;
void *ubuf[] CRYPTO_MINALIGN_ATTR;
};
@@ -200,23 +201,38 @@ static void ahash_op_unaligned_finish(struct ahash_request *req, int err)
if (!err)
memcpy(priv->result, req->result,
crypto_ahash_digestsize(crypto_ahash_reqtfm(req)));
-
- kzfree(priv);
}
-static void ahash_op_unaligned_done(struct crypto_async_request *req, int err)
+static void ahash_op_unaligned_done(struct crypto_async_request *areq, 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;
+ struct ahash_request *req = areq->data;
+ struct ahash_request_priv *priv = req->priv;
+ struct crypto_async_request *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 req->result into req->priv.result */
+ ahash_op_unaligned_finish(req, err);
- ahash_op_unaligned_finish(areq, err);
+ /* Restore the original crypto request. */
+ req->result = priv->result;
+ req->base.complete = priv->complete;
+ req->base.data = priv->data;
+ req->priv = priv->priv;
- areq->base.complete = complete;
- areq->base.data = data;
+ /* Free the req->priv.priv from the ADJUSTED request. */
+ kzfree(priv);
- complete(&areq->base, err);
+ /* Complete the ORIGINAL request. */
+ data = req->base.data;
+ req->base.complete(data, err);
}
static int ahash_op_unaligned(struct ahash_request *req,
@@ -234,9 +250,36 @@ 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 = ORIGINAL(priv)
+ * }
+ */
+
priv->result = req->result;
priv->complete = req->base.complete;
priv->data = req->base.data;
+ priv->priv = req->priv;
req->result = PTR_ALIGN((u8 *)priv->ubuf, alignmask + 1);
req->base.complete = ahash_op_unaligned_done;
--
1.8.5.2
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