crypto: hash - introduce crypto_shash_tfm_digest()

Currently the simplest use of the shash API is to use
crypto_shash_digest() to digest a whole buffer.  However, this still
requires allocating a hash descriptor (struct shash_desc).  Many users
don't really want to preallocate one and instead just use a one-off
descriptor on the stack like the following:

	{
		SHASH_DESC_ON_STACK(desc, tfm);
		int err;

		desc->tfm = tfm;

		err = crypto_shash_digest(desc, data, len, out);

		shash_desc_zero(desc);
	}

Wrap this in a new helper function crypto_shash_tfm_digest() that can be
used instead of the above.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/shash.c

@@ -206,6 +206,22 @@ int crypto_shash_digest(struct shash_desc *desc, const u8 *data,
 }
 EXPORT_SYMBOL_GPL(crypto_shash_digest);
 
+int crypto_shash_tfm_digest(struct crypto_shash *tfm, const u8 *data,
+			    unsigned int len, u8 *out)
+{
+	SHASH_DESC_ON_STACK(desc, tfm);
+	int err;
+
+	desc->tfm = tfm;
+
+	err = crypto_shash_digest(desc, data, len, out);
+
+	shash_desc_zero(desc);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(crypto_shash_tfm_digest);
+
 static int shash_default_export(struct shash_desc *desc, void *out)
 {
 	memcpy(out, shash_desc_ctx(desc), crypto_shash_descsize(desc->tfm));

include/crypto/hash.h

@@ -855,6 +855,25 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key,
 int crypto_shash_digest(struct shash_desc *desc, const u8 *data,
 			unsigned int len, u8 *out);
 
+/**
+ * crypto_shash_tfm_digest() - calculate message digest for buffer
+ * @tfm: hash transformation object
+ * @data: see crypto_shash_update()
+ * @len: see crypto_shash_update()
+ * @out: see crypto_shash_final()
+ *
+ * This is a simplified version of crypto_shash_digest() for users who don't
+ * want to allocate their own hash descriptor (shash_desc).  Instead,
+ * crypto_shash_tfm_digest() takes a hash transformation object (crypto_shash)
+ * directly, and it allocates a hash descriptor on the stack internally.
+ * Note that this stack allocation may be fairly large.
+ *
+ * Context: Any context.
+ * Return: 0 on success; < 0 if an error occurred.
+ */
+int crypto_shash_tfm_digest(struct crypto_shash *tfm, const u8 *data,
+			    unsigned int len, u8 *out);
+
 /**
  * crypto_shash_export() - extract operational state for message digest
  * @desc: reference to the operational state handle whose state is exported