linux-kernel - Re: [PATCH v6 6/6] crypto: AF_ALG

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Date:	Wed, 25 May 2016 17:45:48 -0700 (PDT)
From:	Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:	Tadeusz Struk <tadeusz.struk@...el.com>
cc:	dhowells@...hat.com, herbert@...dor.apana.org.au,
	smueller@...onox.de, linux-api@...r.kernel.org,
	marcel@...tmann.org, linux-kernel@...r.kernel.org,
	keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
	dwmw2@...radead.org, davem@...emloft.net
Subject: Re: [PATCH v6 6/6] crypto: AF_ALG - add support for key_id

On Sat, 14 May 2016, Tadeusz Struk wrote:

> diff --git a/crypto/algif_akcipher.c b/crypto/algif_akcipher.c
> index e00793d..6733df1 100644
> --- a/crypto/algif_akcipher.c
> +++ b/crypto/algif_akcipher.c
> +static int asym_key_verify(const struct key *key, struct akcipher_request *req)
> +{
> +	struct public_key_signature sig;
> +	char *src = NULL, *in;
> +	int ret;
> +
> +	if (!sg_is_last(req->src)) {
> +		src = kmalloc(req->src_len, GFP_KERNEL);
> +		if (!src)
> +			return -ENOMEM;
> +		scatterwalk_map_and_copy(src, req->src, 0, req->src_len, 0);
> +		in = src;
> +	} else {
> +		in = sg_virt(req->src);
> +	}
> +	sig.pkey_algo = "rsa";
> +	sig.encoding = "pkcs1";
> +	/* Need to find a way to pass the hash param */

Are you referring to sig.digest here? It looks like you will hit a 
BUG_ON() in public_key_verify_signature() if sig.digest is 0. However, 
sig.digest is unlikely to be 0 because the struct is not cleared - should 
fix this, since public_key_verify_signature() will try to follow that 
random pointer.

> +	sig.hash_algo = "sha1";
> +	sig.digest_size = 20;
> +	sig.s_size = req->src_len;
> +	sig.s = src;
> +	ret = verify_signature(key, NULL, &sig);

Is the idea to write the signature to the socket, and then read out the 
expected digest (the digest comparison being done elsewhere)? Is that 
something that will be supported by a future hardware asymmetric key 
subtype?

verify_signature() ends up calling public_key_verify_signature(), which 
currently expects to get both the digest and signature as input and 
returns an error if verification fails. The output of 
crypto_akcipher_verify() is discarded before public_key_verify_signature() 
returns so nothing ends up in req->dst to read from the socket.

ALG_OP_VERIFY should behave the same whether using ALG_SET_PUBKEY or 
ALG_SET_PUBKEY_ID, and they aren't right now.

If sig.digest is 0, verify_signature() could return the expected digest in 
the sig structure and skip the digest comparison it currently does. Then 
that data could be packaged up in req as if crypto_akcipher_verify() had 
been called. I don't know if this change confuses the semantics of 
verify_signature() too much, maybe a new function is required with all the 
requisite plumbing to the asymmetric key subtype.

--
Mat Martineau
Intel OTC