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>

2 files changed, 3 insertions, 3 deletions

diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index af3eb02bbca1..f6a17d259db7 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -838,7 +838,7 @@ ecryptfs_write_tag_70_packet(char *dest, size_t *remaining_bytes,
 out_release_free_unlock:
 	crypto_free_shash(s->hash_tfm);
 out_free_unlock:
-	kzfree(s->block_aligned_filename);
+	kfree_sensitive(s->block_aligned_filename);
 out_unlock:
 	mutex_unlock(s->tfm_mutex);
 out:
@@ -847,7 +847,7 @@ out:
 		key_put(auth_tok_key);
 	}
 	skcipher_request_free(s->skcipher_req);
-	kzfree(s->hash_desc);
+	kfree_sensitive(s->hash_desc);
 	kfree(s);
 	return rc;
 }
diff --git a/fs/ecryptfs/messaging.c b/fs/ecryptfs/messaging.c
index 8646ba76def3..c0dfd9647627 100644
--- a/fs/ecryptfs/messaging.c
+++ b/fs/ecryptfs/messaging.c
@@ -175,7 +175,7 @@ int ecryptfs_exorcise_daemon(struct ecryptfs_daemon *daemon)
 	}
 	hlist_del(&daemon->euid_chain);
 	mutex_unlock(&daemon->mux);
-	kzfree(daemon);
+	kfree_sensitive(daemon);
 out:
 	return rc;
 }