crypto: algapi - enforce that all instances have a ->free() method

All instances need to have a ->free() method, but people could forget to
set it and then not notice if the instance is never unregistered. To
help detect this bug earlier, don't allow an instance without a ->free()
method to be registered, and complain loudly if someone tries to do it.

Signed-off-by: Eric Biggers <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

crypto/aead.c

···
 {
 	int err;
 
+	if (WARN_ON(!inst->free))
+		return -EINVAL;
+
 	err = aead_prepare_alg(&inst->alg);
 	if (err)
 		return err;

crypto/ahash.c

···
 {
 	int err;
 
+	if (WARN_ON(!inst->free))
+		return -EINVAL;
+
 	err = ahash_prepare_alg(&inst->alg);
 	if (err)
 		return err;

crypto/akcipher.c

···
 int akcipher_register_instance(struct crypto_template *tmpl,
 			       struct akcipher_instance *inst)
 {
+	if (WARN_ON(!inst->free))
+		return -EINVAL;
 	akcipher_prepare_alg(&inst->alg);
 	return crypto_register_instance(tmpl, akcipher_crypto_instance(inst));
 }

crypto/shash.c

···
 {
 	int err;
 
+	if (WARN_ON(!inst->free))
+		return -EINVAL;
+
 	err = shash_prepare_alg(&inst->alg);
 	if (err)
 		return err;

crypto/skcipher.c

···
 {
 	int err;
 
+	if (WARN_ON(!inst->free))
+		return -EINVAL;
+
 	err = skcipher_prepare_alg(&inst->alg);
 	if (err)
 		return err;