SUNRPC: Remove .blocksize field from struct gss_krb5_enctype

It is not clear from documenting comments, specifications, or code
usage what value the gss_krb5_enctype.blocksize field is supposed
to store. The "encryption blocksize" depends only on the cipher
being used, so that value can be derived where it's needed instead
of stored as a constant.

RFC 3961 Section 5.2 says:

> cipher block size, c
>    This is the block size of the block cipher underlying the
>    encryption and decryption functions indicated above, used for key
>    derivation and for the size of the message confounder and initial
>    vector.  (If a block cipher is not in use, some comparable
>    parameter should be determined.)  It must be at least 5 octets.
>
>    This is not actually an independent parameter; rather, it is a
>    property of the functions E and D.  It is listed here to clarify
>    the distinction between it and the message block size, m.

In the Linux kernel's implemenation of the SunRPC RPCSEC GSS
Kerberos 5 mechanism, the cipher block size, which is dependent on
the encryption and decryption transforms, is used only in
krb5_derive_key(), so it is straightforward to replace it.

Tested-by: Scott Mayhew <[email protected]>
Reviewed-by: Simo Sorce <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>

1 files changed, 1 insertions, 3 deletions

diff --git a/net/sunrpc/auth_gss/gss_krb5_keys.c b/net/sunrpc/auth_gss/gss_krb5_keys.c
index 726c076950c0..554cfd23f288 100644
--- a/net/sunrpc/auth_gss/gss_krb5_keys.c
+++ b/net/sunrpc/auth_gss/gss_krb5_keys.c
@@ -150,7 +150,6 @@ u32 krb5_derive_key(const struct gss_krb5_enctype *gk5e,
 	struct crypto_sync_skcipher *cipher;
 	u32 ret = EINVAL;
 
-	blocksize = gk5e->blocksize;
 	keybytes = gk5e->keybytes;
 	keylength = gk5e->keylength;
 
@@ -160,11 +159,10 @@ u32 krb5_derive_key(const struct gss_krb5_enctype *gk5e,
 	cipher = crypto_alloc_sync_skcipher(gk5e->encrypt_name, 0, 0);
 	if (IS_ERR(cipher))
 		goto err_return;
+	blocksize = crypto_sync_skcipher_blocksize(cipher);
 	if (crypto_sync_skcipher_setkey(cipher, inkey->data, inkey->len))
 		goto err_return;
 
-	/* allocate and set up buffers */
-
 	ret = ENOMEM;
 	inblockdata = kmalloc(blocksize, gfp_mask);
 	if (inblockdata == NULL)