Re: [PATCH v6 6/6] crypto: AF_ALG - add support for key_id

Mat Martineau
2016-05-26T00:46:09Z

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