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 <smayhew@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/gss_krb5.h

@@ -64,7 +64,6 @@ struct gss_krb5_enctype {
 	const char		*cksum_name;	/* crypto checksum name */
 	const u16		signalg;	/* signing algorithm */
 	const u16		sealalg;	/* sealing algorithm */
-	const u32		blocksize;	/* encryption blocksize */
 	const u32		conflen;	/* confounder length
 						   (normally the same as
 						   the blocksize) */

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)

net/sunrpc/auth_gss/gss_krb5_mech.c

@@ -47,7 +47,6 @@ static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
 	  .sealalg = SEAL_ALG_DES,
 	  .keybytes = 7,
 	  .keylength = 8,
-	  .blocksize = 8,
 	  .conflen = 8,
 	  .cksumlength = 8,
 	  .keyed_cksum = 0,
@@ -69,7 +68,6 @@ static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
 	  .sealalg = SEAL_ALG_DES3KD,
 	  .keybytes = 21,
 	  .keylength = 24,
-	  .blocksize = 8,
 	  .conflen = 8,
 	  .cksumlength = 20,
 	  .keyed_cksum = 1,
@@ -92,7 +90,6 @@ static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
 	  .sealalg = -1,
 	  .keybytes = 16,
 	  .keylength = 16,
-	  .blocksize = 16,
 	  .conflen = 16,
 	  .cksumlength = 12,
 	  .keyed_cksum = 1,
@@ -115,7 +112,6 @@ static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
 	  .sealalg = -1,
 	  .keybytes = 32,
 	  .keylength = 32,
-	  .blocksize = 16,
 	  .conflen = 16,
 	  .cksumlength = 12,
 	  .keyed_cksum = 1,