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

From: Mat Martineau
Date: Wed May 25 2016 - 20:46:11 EST

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