[PATCH 2/2] KEYS: asymmetric: properly validate hash_algo and encoding

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

It is insecure to allow arbitrary hash algorithms and signature
encodings to be used with arbitrary signature algorithms.  Notably,
ECDSA, ECRDSA, and SM2 all sign/verify raw hash values and don't
disambiguate between different hash algorithms like RSA PKCS#1 v1.5
padding does.  Therefore, they need to be restricted to certain sets of
hash algorithms (ideally just one, but in practice small sets are used).
Additionally, the encoding is an integral part of modern signature
algorithms, and is not supposed to vary.

Therefore, tighten the checks of hash_algo and encoding done by
software_key_determine_akcipher().

Also rearrange the parameters to software_key_determine_akcipher() to
put the public_key first, as this is the most important parameter and it
often determines everything else.

Fixes: 299f561a6693 ("x509: Add support for parsing x509 certs with ECDSA keys")
Fixes: 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")
Fixes: 0d7a78643f69 ("crypto: ecrdsa - add EC-RDSA (GOST 34.10) algorithm")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/asymmetric_keys/public_key.c | 111 +++++++++++++++++++---------
 1 file changed, 76 insertions(+), 35 deletions(-)

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index aba7113d86c76..a603ee8afdb8d 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -60,39 +60,83 @@ static void public_key_destroy(void *payload0, void *payload3)
 }
 
 /*
- * Determine the crypto algorithm name.
+ * Given a public_key, and an encoding and hash_algo to be used for signing
+ * and/or verification with that key, determine the name of the corresponding
+ * akcipher algorithm.  Also check that encoding and hash_algo are allowed.
  */
-static
-int software_key_determine_akcipher(const char *encoding,
-				    const char *hash_algo,
-				    const struct public_key *pkey,
-				    char alg_name[CRYPTO_MAX_ALG_NAME])
+static int
+software_key_determine_akcipher(const struct public_key *pkey,
+				const char *encoding, const char *hash_algo,
+				char alg_name[CRYPTO_MAX_ALG_NAME])
 {
 	int n;
 
-	if (strcmp(encoding, "pkcs1") == 0) {
-		/* The data wangled by the RSA algorithm is typically padded
-		 * and encoded in some manner, such as EMSA-PKCS1-1_5 [RFC3447
-		 * sec 8.2].
+	if (!encoding)
+		return -EINVAL;
+
+	if (strcmp(pkey->pkey_algo, "rsa") == 0) {
+		/*
+		 * RSA signatures usually use EMSA-PKCS1-1_5 [RFC3447 sec 8.2].
+		 */
+		if (strcmp(encoding, "pkcs1") == 0) {
+			if (!hash_algo)
+				n = snprintf(alg_name, CRYPTO_MAX_ALG_NAME,
+					     "pkcs1pad(%s)",
+					     pkey->pkey_algo);
+			else
+				n = snprintf(alg_name, CRYPTO_MAX_ALG_NAME,
+					     "pkcs1pad(%s,%s)",
+					     pkey->pkey_algo, hash_algo);
+			return n >= CRYPTO_MAX_ALG_NAME ? -EINVAL : 0;
+		}
+		if (strcmp(encoding, "raw") != 0)
+			return -EINVAL;
+		/*
+		 * Raw RSA cannot differentiate between different hash
+		 * algorithms.
+		 */
+		if (hash_algo)
+			return -EINVAL;
+	} else if (strncmp(pkey->pkey_algo, "ecdsa", 5) == 0) {
+		if (strcmp(encoding, "x962") != 0)
+			return -EINVAL;
+		/*
+		 * ECDSA signatures are taken over a raw hash, so they don't
+		 * differentiate between different hash algorithms.  That means
+		 * that the verifier should hard-code a specific hash algorithm.
+		 * Unfortunately, in practice ECDSA is used with multiple SHAs,
+		 * so we have to allow all of them and not just one.
 		 */
 		if (!hash_algo)
-			n = snprintf(alg_name, CRYPTO_MAX_ALG_NAME,
-				     "pkcs1pad(%s)",
-				     pkey->pkey_algo);
-		else
-			n = snprintf(alg_name, CRYPTO_MAX_ALG_NAME,
-				     "pkcs1pad(%s,%s)",
-				     pkey->pkey_algo, hash_algo);
-		return n >= CRYPTO_MAX_ALG_NAME ? -EINVAL : 0;
-	}
-
-	if (strcmp(encoding, "raw") == 0 ||
-	    strcmp(encoding, "x962") == 0) {
-		strcpy(alg_name, pkey->pkey_algo);
-		return 0;
+			return -EINVAL;
+		if (strcmp(hash_algo, "sha1") != 0 &&
+		    strcmp(hash_algo, "sha224") != 0 &&
+		    strcmp(hash_algo, "sha256") != 0 &&
+		    strcmp(hash_algo, "sha384") != 0 &&
+		    strcmp(hash_algo, "sha512") != 0)
+			return -EINVAL;
+	} else if (strcmp(pkey->pkey_algo, "sm2") == 0) {
+		if (strcmp(encoding, "raw") != 0)
+			return -EINVAL;
+		if (!hash_algo)
+			return -EINVAL;
+		if (strcmp(hash_algo, "sm3") != 0)
+			return -EINVAL;
+	} else if (strcmp(pkey->pkey_algo, "ecrdsa") == 0) {
+		if (strcmp(encoding, "raw") != 0)
+			return -EINVAL;
+		if (!hash_algo)
+			return -EINVAL;
+		if (strcmp(hash_algo, "streebog256") != 0 &&
+		    strcmp(hash_algo, "streebog512") != 0)
+			return -EINVAL;
+	} else {
+		/* Unknown public key algorithm */
+		return -ENOPKG;
 	}
-
-	return -ENOPKG;
+	if (strscpy(alg_name, pkey->pkey_algo, CRYPTO_MAX_ALG_NAME) < 0)
+		return -EINVAL;
+	return 0;
 }
 
 static u8 *pkey_pack_u32(u8 *dst, u32 val)
@@ -113,9 +157,8 @@ static int software_key_query(const struct kernel_pkey_params *params,
 	u8 *key, *ptr;
 	int ret, len;
 
-	ret = software_key_determine_akcipher(params->encoding,
-					      params->hash_algo,
-					      pkey, alg_name);
+	ret = software_key_determine_akcipher(pkey, params->encoding,
+					      params->hash_algo, alg_name);
 	if (ret < 0)
 		return ret;
 
@@ -179,9 +222,8 @@ static int software_key_eds_op(struct kernel_pkey_params *params,
 
 	pr_devel("==>%s()\n", __func__);
 
-	ret = software_key_determine_akcipher(params->encoding,
-					      params->hash_algo,
-					      pkey, alg_name);
+	ret = software_key_determine_akcipher(pkey, params->encoding,
+					      params->hash_algo, alg_name);
 	if (ret < 0)
 		return ret;
 
@@ -340,9 +382,8 @@ int public_key_verify_signature(const struct public_key *pkey,
 	     strcmp(sig->pkey_algo, "ecdsa") != 0))
 		return -EKEYREJECTED;
 
-	ret = software_key_determine_akcipher(sig->encoding,
-					      sig->hash_algo,
-					      pkey, alg_name);
+	ret = software_key_determine_akcipher(pkey, sig->encoding,
+					      sig->hash_algo, alg_name);
 	if (ret < 0)
 		return ret;
 
-- 
2.35.1