crypto: akcipher - new verify API for public key algorithms

Previous akcipher .verify() just `decrypts' (using RSA encrypt which is
using public key) signature to uncover message hash, which was then
compared in upper level public_key_verify_signature() with the expected
hash value, which itself was never passed into verify().

This approach was incompatible with EC-DSA family of algorithms,
because, to verify a signature EC-DSA algorithm also needs a hash value
as input; then it's used (together with a signature divided into halves
`r||s') to produce a witness value, which is then compared with `r' to
determine if the signature is correct. Thus, for EC-DSA, nor
requirements of .verify() itself, nor its output expectations in
public_key_verify_signature() wasn't sufficient.

Make improved .verify() call which gets hash value as input and produce
complete signature check without any output besides status.

Now for the top level verification only crypto_akcipher_verify() needs
to be called and its return value inspected.

Make sure that `digest' is in kmalloc'd memory (in place of `output`) in
{public,tpm}_key_verify_signature() as insisted by Herbert Xu, and will
be changed in the following commit.

Cc: David Howells <dhowells@redhat.com>
Cc: keyrings@vger.kernel.org
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
Reviewed-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 19 insertions, 10 deletions

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index 94382fa2c6ac..29c336068dc0 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -488,14 +488,21 @@ static int pkcs1pad_verify_complete(struct akcipher_request *req, int err)
 
 	err = 0;
 
-	if (req->dst_len < dst_len - pos)
-		err = -EOVERFLOW;
-	req->dst_len = dst_len - pos;
-
-	if (!err)
-		sg_copy_from_buffer(req->dst,
-				sg_nents_for_len(req->dst, req->dst_len),
-				out_buf + pos, req->dst_len);
+	if (req->dst_len != dst_len - pos) {
+		err = -EKEYREJECTED;
+		req->dst_len = dst_len - pos;
+		goto done;
+	}
+	/* Extract appended digest. */
+	sg_pcopy_to_buffer(req->src,
+			   sg_nents_for_len(req->src,
+					    req->src_len + req->dst_len),
+			   req_ctx->out_buf + ctx->key_size,
+			   req->dst_len, ctx->key_size);
+	/* Do the actual verification step. */
+	if (memcmp(req_ctx->out_buf + ctx->key_size, out_buf + pos,
+		   req->dst_len) != 0)
+		err = -EKEYREJECTED;
 done:
 	kzfree(req_ctx->out_buf);
 
@@ -532,10 +539,12 @@ static int pkcs1pad_verify(struct akcipher_request *req)
 	struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
 	int err;
 
-	if (!ctx->key_size || req->src_len < ctx->key_size)
+	if (WARN_ON(req->dst) ||
+	    WARN_ON(!req->dst_len) ||
+	    !ctx->key_size || req->src_len < ctx->key_size)
 		return -EINVAL;
 
-	req_ctx->out_buf = kmalloc(ctx->key_size, GFP_KERNEL);
+	req_ctx->out_buf = kmalloc(ctx->key_size + req->dst_len, GFP_KERNEL);
 	if (!req_ctx->out_buf)
 		return -ENOMEM;