crypto/krb5: Add an API to alloc and prepare a crypto object

Add an API by which users of the krb5 crypto library can get an allocated
and keyed crypto object.

For encryption-mode operation, an AEAD object is returned; for
checksum-mode operation, a synchronous hash object is returned.

Signed-off-by: David Howells <[e-mail]>
cc: Herbert Xu <[e-mail]>
cc: "David S. Miller" <[e-mail]>
cc: Chuck Lever <[e-mail]>
cc: Marc Dionne <[e-mail]>
cc: Eric Dumazet <[e-mail]>
cc: Jakub Kicinski <[e-mail]>
cc: Paolo Abeni <[e-mail]>
cc: Simon Horman <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]

crypto/krb5/internal.h

···
 #define krb5_digest_size(TFM) \
 	crypto_roundup(crypto_shash_digestsize(TFM))
 #define round16(x) (((x) + 15) & ~15)
+
+/*
+ * krb5_api.c
+ */
+struct crypto_aead *krb5_prepare_encryption(const struct krb5_enctype *krb5,
+					    const struct krb5_buffer *keys,
+					    gfp_t gfp);
+struct crypto_shash *krb5_prepare_checksum(const struct krb5_enctype *krb5,
+					   const struct krb5_buffer *Kc,
+					   gfp_t gfp);

crypto/krb5/krb5_api.c

···
 	}
 }
 EXPORT_SYMBOL(crypto_krb5_where_is_the_data);
+
+/*
+ * Prepare the encryption with derived key data.
+ */
+struct crypto_aead *krb5_prepare_encryption(const struct krb5_enctype *krb5,
+					    const struct krb5_buffer *keys,
+					    gfp_t gfp)
+{
+	struct crypto_aead *ci = NULL;
+	int ret = -ENOMEM;
+
+	ci = crypto_alloc_aead(krb5->encrypt_name, 0, 0);
+	if (IS_ERR(ci)) {
+		ret = PTR_ERR(ci);
+		if (ret == -ENOENT)
+			ret = -ENOPKG;
+		goto err;
+	}
+
+	ret = crypto_aead_setkey(ci, keys->data, keys->len);
+	if (ret < 0) {
+		pr_err("Couldn't set AEAD key %s: %d\n", krb5->encrypt_name, ret);
+		goto err_ci;
+	}
+
+	ret = crypto_aead_setauthsize(ci, krb5->cksum_len);
+	if (ret < 0) {
+		pr_err("Couldn't set AEAD authsize %s: %d\n", krb5->encrypt_name, ret);
+		goto err_ci;
+	}
+
+	return ci;
+err_ci:
+	crypto_free_aead(ci);
+err:
+	return ERR_PTR(ret);
+}
+
+/**
+ * crypto_krb5_prepare_encryption - Prepare AEAD crypto object for encryption-mode
+ * @krb5: The encoding to use.
+ * @TK: The transport key to use.
+ * @usage: The usage constant for key derivation.
+ * @gfp: Allocation flags.
+ *
+ * Allocate a crypto object that does all the necessary crypto, key it and set
+ * its parameters and return the crypto handle to it.  This can then be used to
+ * dispatch encrypt and decrypt operations.
+ */
+struct crypto_aead *crypto_krb5_prepare_encryption(const struct krb5_enctype *krb5,
+						   const struct krb5_buffer *TK,
+						   u32 usage, gfp_t gfp)
+{
+	struct crypto_aead *ci = NULL;
+	struct krb5_buffer keys = {};
+	int ret;
+
+	ret = krb5->profile->derive_encrypt_keys(krb5, TK, usage, &keys, gfp);
+	if (ret < 0)
+		goto err;
+
+	ci = krb5_prepare_encryption(krb5, &keys, gfp);
+	if (IS_ERR(ci)) {
+		ret = PTR_ERR(ci);
+		goto err;
+	}
+
+	kfree(keys.data);
+	return ci;
+err:
+	kfree(keys.data);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL(crypto_krb5_prepare_encryption);
+
+/*
+ * Prepare the checksum with derived key data.
+ */
+struct crypto_shash *krb5_prepare_checksum(const struct krb5_enctype *krb5,
+					   const struct krb5_buffer *Kc,
+					   gfp_t gfp)
+{
+	struct crypto_shash *ci = NULL;
+	int ret = -ENOMEM;
+
+	ci = crypto_alloc_shash(krb5->cksum_name, 0, 0);
+	if (IS_ERR(ci)) {
+		ret = PTR_ERR(ci);
+		if (ret == -ENOENT)
+			ret = -ENOPKG;
+		goto err;
+	}
+
+	ret = crypto_shash_setkey(ci, Kc->data, Kc->len);
+	if (ret < 0) {
+		pr_err("Couldn't set shash key %s: %d\n", krb5->cksum_name, ret);
+		goto err_ci;
+	}
+
+	return ci;
+err_ci:
+	crypto_free_shash(ci);
+err:
+	return ERR_PTR(ret);
+}
+
+/**
+ * crypto_krb5_prepare_checksum - Prepare AEAD crypto object for checksum-mode
+ * @krb5: The encoding to use.
+ * @TK: The transport key to use.
+ * @usage: The usage constant for key derivation.
+ * @gfp: Allocation flags.
+ *
+ * Allocate a crypto object that does all the necessary crypto, key it and set
+ * its parameters and return the crypto handle to it.  This can then be used to
+ * dispatch get_mic and verify_mic operations.
+ */
+struct crypto_shash *crypto_krb5_prepare_checksum(const struct krb5_enctype *krb5,
+						  const struct krb5_buffer *TK,
+						  u32 usage, gfp_t gfp)
+{
+	struct crypto_shash *ci = NULL;
+	struct krb5_buffer keys = {};
+	int ret;
+
+	ret = krb5->profile->derive_checksum_key(krb5, TK, usage, &keys, gfp);
+	if (ret < 0) {
+		pr_err("get_Kc failed %d\n", ret);
+		goto err;
+	}
+
+	ci = krb5_prepare_checksum(krb5, &keys, gfp);
+	if (IS_ERR(ci)) {
+		ret = PTR_ERR(ci);
+		goto err;
+	}
+
+	kfree(keys.data);
+	return ci;
+err:
+	kfree(keys.data);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL(crypto_krb5_prepare_checksum);

include/crypto/krb5.h

···
 
 #include <linux/crypto.h>
 #include <crypto/aead.h>
+#include <crypto/hash.h>
 
 struct crypto_shash;
 struct scatterlist;
···
 void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
 				   enum krb5_crypto_mode mode,
 				   size_t *_offset, size_t *_len);
+struct crypto_aead *crypto_krb5_prepare_encryption(const struct krb5_enctype *krb5,
+						   const struct krb5_buffer *TK,
+						   u32 usage, gfp_t gfp);
+struct crypto_shash *crypto_krb5_prepare_checksum(const struct krb5_enctype *krb5,
+						  const struct krb5_buffer *TK,
+						  u32 usage, gfp_t gfp);
 
 #endif /* _CRYPTO_KRB5_H */