[PATCH v3 12/18] crypto: rsa-psspad: Introduce shash alloc/dealloc helpers

[Varad Gautam]

RSASSA-PSS verify operation needs to compute digests for its
Mask Generation Function (MGF1), and for digest comparison.

Add helpers to populate a crypto_shash and desc for use in both cases.

Signed-off-by: Varad Gautam <varad.gautam@xxxxxxxx>
---
v3: Add psspad_check_hash_algo to only allow valid hash algorithms in
  psspad_setup_shash.

 crypto/rsa-psspad.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/crypto/rsa-psspad.c b/crypto/rsa-psspad.c
index 0e5422b05c081..40bb6d1dd2067 100644
--- a/crypto/rsa-psspad.c
+++ b/crypto/rsa-psspad.c
@@ -6,9 +6,52 @@
  * Authors: Varad Gautam <varad.gautam@xxxxxxxx>
  */
 
+#include <crypto/hash.h>
 #include <crypto/internal/akcipher.h>
 #include <crypto/internal/rsa-common.h>
 
+static bool psspad_check_hash_algo(const char *hash_algo)
+{
+	const char *hash_algos[] = { "sha1", "sha224", "sha256", "sha384", "sha512" };
+	bool found = false;
+	int i = 0;
+
+	for (i = 0; i < ARRAY_SIZE(hash_algos); i++) {
+		if (strcmp(hash_algo, hash_algos[i]) == 0) {
+			found = true;
+			break;
+		}
+	}
+
+	return found;
+}
+
+static int psspad_setup_shash(struct crypto_shash **hash_tfm, struct shash_desc **desc,
+			      const char *hash_algo)
+{
+	if (!psspad_check_hash_algo(hash_algo))
+		return -EINVAL;
+
+	*hash_tfm = crypto_alloc_shash(hash_algo, 0, 0);
+	if (IS_ERR(*hash_tfm))
+		return PTR_ERR(*hash_tfm);
+
+	*desc = kzalloc(crypto_shash_descsize(*hash_tfm) + sizeof(**desc),
+			GFP_KERNEL);
+	if (!desc)
+		return -ENOMEM;
+
+	(*desc)->tfm = *hash_tfm;
+
+	return 0;
+}
+
+static void psspad_free_shash(struct crypto_shash *hash_tfm, struct shash_desc *desc)
+{
+	kfree(desc);
+	crypto_free_shash(hash_tfm);
+}
+
 static int psspad_s_v_e_d(struct akcipher_request *req)
 {
 	return -EOPNOTSUPP;
-- 
2.30.2