mm, treewide: rename kzfree() to kfree_sensitive()

As said by Linus:

  A symmetric naming is only helpful if it implies symmetries in use.
  Otherwise it's actively misleading.

  In "kzalloc()", the z is meaningful and an important part of what the
  caller wants.

  In "kzfree()", the z is actively detrimental, because maybe in the
  future we really _might_ want to use that "memfill(0xdeadbeef)" or
  something. The "zero" part of the interface isn't even _relevant_.

The main reason that kzfree() exists is to clear sensitive information
that should not be leaked to other future users of the same memory
objects.

Rename kzfree() to kfree_sensitive() to follow the example of the recently
added kvfree_sensitive() and make the intention of the API more explicit.
In addition, memzero_explicit() is used to clear the memory to make sure
that it won't get optimized away by the compiler.

The renaming is done by using the command sequence:

  git grep -w --name-only kzfree |\
  xargs sed -i 's/kzfree/kfree_sensitive/'

followed by some editing of the kfree_sensitive() kerneldoc and adding
a kzfree backward compatibility macro in slab.h.

[akpm@linux-foundation.org: fs/crypto/inline_crypt.c needs linux/slab.h]
[akpm@linux-foundation.org: fix fs/crypto/inline_crypt.c some more]

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Joe Perches <joe@perches.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: "Jason A . Donenfeld" <Jason@zx2c4.com>
Link: http://lkml.kernel.org/r/20200616154311.12314-3-longman@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/crypto/inline_crypt.c

@@ -16,6 +16,7 @@
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
 #include <linux/sched/mm.h>
+#include <linux/slab.h>
 
 #include "fscrypt_private.h"
 
@@ -187,7 +188,7 @@ int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
 fail:
 	for (i = 0; i < queue_refs; i++)
 		blk_put_queue(blk_key->devs[i]);
-	kzfree(blk_key);
+	kfree_sensitive(blk_key);
 	return err;
 }
 
@@ -201,7 +202,7 @@ void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
 			blk_crypto_evict_key(blk_key->devs[i], &blk_key->base);
 			blk_put_queue(blk_key->devs[i]);
 		}
-		kzfree(blk_key);
+		kfree_sensitive(blk_key);
 	}
 }
 

fs/crypto/keyring.c

@@ -51,7 +51,7 @@ static void free_master_key(struct fscrypt_master_key *mk)
 	}
 
 	key_put(mk->mk_users);
-	kzfree(mk);
+	kfree_sensitive(mk);
 }
 
 static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
@@ -531,7 +531,7 @@ static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
 static void fscrypt_provisioning_key_free_preparse(
 					struct key_preparsed_payload *prep)
 {
-	kzfree(prep->payload.data[0]);
+	kfree_sensitive(prep->payload.data[0]);
 }
 
 static void fscrypt_provisioning_key_describe(const struct key *key,
@@ -548,7 +548,7 @@ static void fscrypt_provisioning_key_describe(const struct key *key,
 
 static void fscrypt_provisioning_key_destroy(struct key *key)
 {
-	kzfree(key->payload.data[0]);
+	kfree_sensitive(key->payload.data[0]);
 }
 
 static struct key_type key_type_fscrypt_provisioning = {

fs/crypto/keysetup_v1.c

@@ -155,7 +155,7 @@ static void free_direct_key(struct fscrypt_direct_key *dk)
 {
 	if (dk) {
 		fscrypt_destroy_prepared_key(&dk->dk_key);
-		kzfree(dk);
+		kfree_sensitive(dk);
 	}
 }
 
@@ -283,7 +283,7 @@ static int setup_v1_file_key_derived(struct fscrypt_info *ci,
 
 	err = fscrypt_set_per_file_enc_key(ci, derived_key);
 out:
-	kzfree(derived_key);
+	kfree_sensitive(derived_key);
 	return err;
 }