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Subject[RFC PATCH 2/4] akcipher: Introduce verify2 for public key algorithms
Date
Current akcipher .verify() just decrypts signature to uncover message
hash, which is then verified in upper level public_key_verify_signature
by memcmp with the expected signature value, which is never passed into
verify().

This approach is incompatible with ECDSA algorithms, because, to verify
a signature ECDSA algorithm also needs a hash value as input; also, hash
is used in ECDSA (together with a signature divided into halves `r||s`),
not to produce hash, but to produce a number, which is then compared to
`r` (first part of the signature) to determine if the signature is
correct. Thus, for ECDSA, nor requirements of .verify() itself, nor its
output expectations in public_key_verify_signature aren't satisfied.

Make alternative .verify2() call which gets hash value and produce
complete signature check (without any output, thus max_size() call will
not be needed for verify2() operation).

If .verify2() call is present, it should be used in place of .verify().

Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
---
crypto/asymmetric_keys/public_key.c | 57 ++++++++++++++++++++++++-------------
include/crypto/akcipher.h | 54 +++++++++++++++++++++++++++++++++--
2 files changed, 89 insertions(+), 22 deletions(-)

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index 3bc090b8adef..51dc1c858c7c 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -242,6 +242,7 @@ int public_key_verify_signature(const struct public_key *pkey,
char alg_name[CRYPTO_MAX_ALG_NAME];
void *output;
unsigned int outlen;
+ int verify2;
int ret;

pr_devel("==>%s()\n", __func__);
@@ -279,14 +280,23 @@ int public_key_verify_signature(const struct public_key *pkey,
if (ret)
goto error_free_req;

- ret = -ENOMEM;
- outlen = crypto_akcipher_maxsize(tfm);
- output = kmalloc(outlen, GFP_KERNEL);
- if (!output)
- goto error_free_req;
-
+ verify2 = crypto_akcipher_have_verify2(req);
+ if (!verify2) {
+ /* verify2 does not need output buffer */
+ ret = -ENOMEM;
+ outlen = crypto_akcipher_maxsize(tfm);
+ output = kmalloc(outlen, GFP_KERNEL);
+ if (!output)
+ goto error_free_req;
+
+ sg_init_one(&digest_sg, output, outlen);
+ } else {
+ /* dummy init digest_sg */
+ memset(&digest_sg, 0, sizeof(digest_sg));
+ output = NULL;
+ outlen = 0;
+ }
sg_init_one(&sig_sg, sig->s, sig->s_size);
- sg_init_one(&digest_sg, output, outlen);
akcipher_request_set_crypt(req, &sig_sg, &digest_sg, sig->s_size,
outlen);
crypto_init_wait(&cwait);
@@ -294,18 +304,27 @@ int public_key_verify_signature(const struct public_key *pkey,
CRYPTO_TFM_REQ_MAY_SLEEP,
crypto_req_done, &cwait);

- /* Perform the verification calculation. This doesn't actually do the
- * verification, but rather calculates the hash expected by the
- * signature and returns that to us.
- */
- ret = crypto_wait_req(crypto_akcipher_verify(req), &cwait);
- if (ret)
- goto out_free_output;
-
- /* Do the actual verification step. */
- if (req->dst_len != sig->digest_size ||
- memcmp(sig->digest, output, sig->digest_size) != 0)
- ret = -EKEYREJECTED;
+ if (!verify2) {
+ /* Perform the verification calculation. This doesn't actually
+ * do the verification, but rather calculates the hash expected
+ * by the signature and returns that to us.
+ */
+ ret = crypto_wait_req(crypto_akcipher_verify(req), &cwait);
+ if (ret)
+ goto out_free_output;
+
+ /* Do the actual verification step. */
+ if (req->dst_len != sig->digest_size ||
+ memcmp(sig->digest, output, sig->digest_size) != 0)
+ ret = -EKEYREJECTED;
+ } else {
+ /* Perform full verification in one call. */
+ req->digest = sig->digest;
+ req->digest_len = sig->digest_size;
+ ret = crypto_wait_req(crypto_akcipher_verify2(req), &cwait);
+ if (ret)
+ goto out_free_output;
+ }

out_free_output:
kfree(output);
diff --git a/include/crypto/akcipher.h b/include/crypto/akcipher.h
index 84d68dfb551a..b15a995f6118 100644
--- a/include/crypto/akcipher.h
+++ b/include/crypto/akcipher.h
@@ -28,6 +28,8 @@
* result.
* In case of error where the dst sgl size was insufficient,
* it will be updated to the size required for the operation.
+ * @digest: Digest for verify2.
+ * @digest_len: Size of the digest.
* @__ctx: Start of private context data
*/
struct akcipher_request {
@@ -36,6 +38,8 @@ struct akcipher_request {
struct scatterlist *dst;
unsigned int src_len;
unsigned int dst_len;
+ u8 *digest;
+ u8 digest_len;
void *__ctx[] CRYPTO_MINALIGN_ATTR;
};

@@ -60,6 +64,8 @@ struct crypto_akcipher {
* algorithm. In case of error, where the dst_len was insufficient,
* the req->dst_len will be updated to the size required for the
* operation
+ * @verify2: Function performs a verify operation as defined by public key
+ * algorithm.
* @encrypt: Function performs an encrypt operation as defined by public key
* algorithm. In case of error, where the dst_len was insufficient,
* the req->dst_len will be updated to the size required for the
@@ -96,6 +102,7 @@ struct crypto_akcipher {
struct akcipher_alg {
int (*sign)(struct akcipher_request *req);
int (*verify)(struct akcipher_request *req);
+ int (*verify2)(struct akcipher_request *req);
int (*encrypt)(struct akcipher_request *req);
int (*decrypt)(struct akcipher_request *req);
int (*set_pub_key)(struct crypto_akcipher *tfm, const void *key,
@@ -400,11 +407,13 @@ static inline int crypto_akcipher_sign(struct akcipher_request *req)
* crypto_akcipher_verify() - Invoke public key verify operation
*
* Function invokes the specific public key verify operation for a given
- * public key algorithm
+ * public key algorithm: basically it does (rsa) decrypt of signature
+ * producing decrypted hash into dst, which should be compared by a caller
+ * with expected hash value.
*
- * @req: asymmetric key request
+ * @req: asymmetric key request (without hash)
*
- * Return: zero on success; error code in case of error
+ * Return: zero on decryption success; error code in case of error
*/
static inline int crypto_akcipher_verify(struct akcipher_request *req)
{
@@ -418,6 +427,45 @@ static inline int crypto_akcipher_verify(struct akcipher_request *req)
}

/**
+ * crypto_akcipher_verify2() - Invoke public key verify operation
+ *
+ * Function performs complete public key verify operation for a given
+ * public key algorithm
+ *
+ * @req: asymmetric key request (with hash)
+ *
+ * Return: zero on verification success; error code in case of error
+ */
+static inline int crypto_akcipher_verify2(struct akcipher_request *req)
+{
+ struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
+ struct akcipher_alg *alg = crypto_akcipher_alg(tfm);
+ int ret;
+
+ ret = alg->verify2(req);
+ crypto_stat_akcipher_verify(req, ret);
+ return ret;
+}
+
+/**
+ * crypto_akcipher_have_verify2() - Check for existence of public key verify2
+ * operation
+ *
+ * Function checks for existence of verify2 call for the public key algorithm
+ *
+ * @req: asymmetric key request (with hash)
+ *
+ * Return: non-zero is verify2 call exists; zero if it does not
+ */
+static inline int crypto_akcipher_have_verify2(struct akcipher_request *req)
+{
+ struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
+ struct akcipher_alg *alg = crypto_akcipher_alg(tfm);
+
+ return !!alg->verify2;
+}
+
+/**
* crypto_akcipher_set_pub_key() - Invoke set public key operation
*
* Function invokes the algorithm specific set key function, which knows
--
2.11.0
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