crypto: sig - Prepare for algorithms with variable signature size

The callers of crypto_sig_sign() assume that the signature size is
always equivalent to the key size.

This happens to be true for RSA, which is currently the only algorithm
implementing the ->sign() callback.  But it is false e.g. for X9.62
encoded ECDSA signatures because they have variable length.

Prepare for addition of a ->sign() callback to such algorithms by
letting the callback return the signature size (or a negative integer
on error).  When testing the ->sign() callback in test_sig_one(),
use crypto_sig_maxsize() instead of crypto_sig_keysize() to verify that
the test vector's signature does not exceed an algorithm's maximum
signature size.

There has been a relatively recent effort to upstream ECDSA signature
generation support which may benefit from this change:

https://lore.kernel.org/linux-crypto/20220908200036.2034-1-ignat@cloudflare.com/

However the main motivation for this commit is to reduce the number of
crypto_sig_keysize() callers:  This function is about to be changed to
return the size in bits instead of bytes and that will require amending
most callers to divide the return value by 8.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Cc: Ignat Korchagin <ignat@cloudflare.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

3 files changed, 7 insertions, 11 deletions

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index bbd07a9022e6..bf165d321440 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -267,7 +267,6 @@ static int software_key_eds_op(struct kernel_pkey_params *params,
 	struct crypto_sig *sig;
 	char *key, *ptr;
 	bool issig;
-	int ksz;
 	int ret;
 
 	pr_devel("==>%s()\n", __func__);
@@ -302,8 +301,6 @@ static int software_key_eds_op(struct kernel_pkey_params *params,
 			ret = crypto_sig_set_pubkey(sig, key, pkey->keylen);
 		if (ret)
 			goto error_free_tfm;
-
-		ksz = crypto_sig_keysize(sig);
 	} else {
 		tfm = crypto_alloc_akcipher(alg_name, 0, 0);
 		if (IS_ERR(tfm)) {
@@ -317,8 +314,6 @@ static int software_key_eds_op(struct kernel_pkey_params *params,
 			ret = crypto_akcipher_set_pub_key(tfm, key, pkey->keylen);
 		if (ret)
 			goto error_free_tfm;
-
-		ksz = crypto_akcipher_maxsize(tfm);
 	}
 
 	ret = -EINVAL;
@@ -347,8 +342,8 @@ static int software_key_eds_op(struct kernel_pkey_params *params,
 		BUG();
 	}
 
-	if (ret == 0)
-		ret = ksz;
+	if (!issig && ret == 0)
+		ret = crypto_akcipher_maxsize(tfm);
 
 error_free_tfm:
 	if (issig)
diff --git a/crypto/rsassa-pkcs1.c b/crypto/rsassa-pkcs1.c
index f68ffd338f48..d01ac75635e0 100644
--- a/crypto/rsassa-pkcs1.c
+++ b/crypto/rsassa-pkcs1.c
@@ -210,7 +210,7 @@ static int rsassa_pkcs1_sign(struct crypto_sig *tfm,
 		memset(dst, 0, pad_len);
 	}
 
-	return 0;
+	return ctx->key_size;
 }
 
 static int rsassa_pkcs1_verify(struct crypto_sig *tfm,
diff --git a/crypto/testmgr.c b/crypto/testmgr.c
index e61490ba4095..b69877db3f33 100644
--- a/crypto/testmgr.c
+++ b/crypto/testmgr.c
@@ -4328,7 +4328,7 @@ static int test_sig_one(struct crypto_sig *tfm, const struct sig_testvec *vecs)
 	if (vecs->public_key_vec)
 		return 0;
 
-	sig_size = crypto_sig_keysize(tfm);
+	sig_size = crypto_sig_maxsize(tfm);
 	if (sig_size < vecs->c_size) {
 		pr_err("alg: sig: invalid maxsize %u\n", sig_size);
 		return -EINVAL;
@@ -4340,13 +4340,14 @@ static int test_sig_one(struct crypto_sig *tfm, const struct sig_testvec *vecs)
 
 	/* Run asymmetric signature generation */
 	err = crypto_sig_sign(tfm, vecs->m, vecs->m_size, sig, sig_size);
-	if (err) {
+	if (err < 0) {
 		pr_err("alg: sig: sign test failed: err %d\n", err);
 		return err;
 	}
 
 	/* Verify that generated signature equals cooked signature */
-	if (memcmp(sig, vecs->c, vecs->c_size) ||
+	if (err != vecs->c_size ||
+	    memcmp(sig, vecs->c, vecs->c_size) ||
 	    memchr_inv(sig + vecs->c_size, 0, sig_size - vecs->c_size)) {
 		pr_err("alg: sig: sign test failed: invalid output\n");
 		hexdump(sig, sig_size);