crypto: skcipher - Allow sync algorithms with large request contexts

Some sync algorithms may require a large amount of temporary
space during its operations.  There is no reason why they should
be limited just because some legacy users want to place all
temporary data on the stack.

Such algorithms can now set a flag to indicate that they need
extra request context, which will cause them to be invisible
to users that go through the sync_skcipher interface.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/skcipher.c

@@ -763,7 +763,7 @@ struct crypto_sync_skcipher *crypto_alloc_sync_skcipher(
 	struct crypto_skcipher *tfm;
 
 	/* Only sync algorithms allowed. */
-	mask |= CRYPTO_ALG_ASYNC;
+	mask |= CRYPTO_ALG_ASYNC | CRYPTO_ALG_SKCIPHER_REQSIZE_LARGE;
 
 	tfm = crypto_alloc_tfm(alg_name, &crypto_skcipher_type, type, mask);
 

include/crypto/internal/skcipher.h

@@ -14,6 +14,14 @@
 #include <linux/list.h>
 #include <linux/types.h>
 
+/*
+ * Set this if your algorithm is sync but needs a reqsize larger
+ * than MAX_SYNC_SKCIPHER_REQSIZE.
+ *
+ * Reuse bit that is specific to hash algorithms.
+ */
+#define CRYPTO_ALG_SKCIPHER_REQSIZE_LARGE CRYPTO_ALG_OPTIONAL_KEY
+
 struct aead_request;
 struct rtattr;