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>

scripts/coccinelle/free/devm_free.cocci

@@ -89,7 +89,7 @@ position p;
 (
  kfree@p(x)
 |
- kzfree@p(x)
+ kfree_sensitive@p(x)
 |
  krealloc@p(x, ...)
 |
@@ -112,7 +112,7 @@ position p != safe.p;
 (
 * kfree@p(x)
 |
-* kzfree@p(x)
+* kfree_sensitive@p(x)
 |
 * krealloc@p(x, ...)
 |

scripts/coccinelle/free/ifnullfree.cocci

@@ -21,7 +21,7 @@ expression E;
 (
   kfree(E);
 |
-  kzfree(E);
+  kfree_sensitive(E);
 |
   debugfs_remove(E);
 |
@@ -42,7 +42,7 @@ position p;
 @@
 
 * if (E != NULL)
-*	\(kfree@p\|kzfree@p\|debugfs_remove@p\|debugfs_remove_recursive@p\|
+*	\(kfree@p\|kfree_sensitive@p\|debugfs_remove@p\|debugfs_remove_recursive@p\|
 *         usb_free_urb@p\|kmem_cache_destroy@p\|mempool_destroy@p\|
 *         dma_pool_destroy@p\)(E);
 

scripts/coccinelle/free/kfree.cocci

@@ -24,7 +24,7 @@ position p1;
 (
 * kfree@p1(E)
 |
-* kzfree@p1(E)
+* kfree_sensitive@p1(E)
 )
 
 @print expression@
@@ -68,7 +68,7 @@ while (1) { ...
 (
 * kfree@ok(E)
 |
-* kzfree@ok(E)
+* kfree_sensitive@ok(E)
 )
   ... when != break;
       when != goto l;
@@ -86,7 +86,7 @@ position free.p1!=loop.ok,p2!={print.p,sz.p};
 (
 * kfree@p1(E,...)
 |
-* kzfree@p1(E,...)
+* kfree_sensitive@p1(E,...)
 )
 ...
 (

scripts/coccinelle/free/kfreeaddr.cocci

@@ -20,7 +20,7 @@ position p;
 (
 * kfree@p(&e->f)
 |
-* kzfree@p(&e->f)
+* kfree_sensitive@p(&e->f)
 )
 
 @script:python depends on org@