[patch 023/163] mm: ksize() should silently accept a NULL pointer

Andrew Morton
2020-08-07T06:18:20Z

From: William Kucharski <william.kucharski@oracle.com>
Subject: mm: ksize() should silently accept a NULL pointer

Other mm routines such as kfree() and kzfree() silently do the right thing
if passed a NULL pointer, so ksize() should do the same.

Link: http://lkml.kernel.org/r/20200616225409.4670-1-william.kucharski@oracle.com
Signed-off-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/slab_common.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)

--- a/mm/slab_common.c~mm-ksize-should-silently-accept-a-null-pointer
+++ a/mm/slab_common.c
@@ -1681,10 +1681,9 @@ static __always_inline void *__do_kreall
gfp_t flags)
{
void *ret;
- size_t ks = 0;
+ size_t ks;

- if (p)
- ks = ksize(p);
+ ks = ksize(p);

if (ks >= new_size) {
p = kasan_krealloc((void *)p, new_size, flags);
@@ -1744,10 +1743,9 @@ void kfree_sensitive(const void *p)
size_t ks;
void *mem = (void *)p;

- if (unlikely(ZERO_OR_NULL_PTR(mem)))
- return;
ks = ksize(mem);
- memzero_explicit(mem, ks);
+ if (ks)
+ memzero_explicit(mem, ks);
kfree(mem);
}
EXPORT_SYMBOL(kfree_sensitive);
@@ -1770,8 +1768,6 @@ size_t ksize(const void *objp)
{
size_t size;

- if (WARN_ON_ONCE(!objp))
- return 0;
/*
* We need to check that the pointed to object is valid, and only then
* unpoison the shadow memory below. We use __kasan_check_read(), to
@@ -1785,7 +1781,7 @@ size_t ksize(const void *objp)
* We want to perform the check before __ksize(), to avoid potentially
* crashing in __ksize() due to accessing invalid metadata.
*/
- if (unlikely(objp == ZERO_SIZE_PTR) || !__kasan_check_read(objp, 1))
+ if (unlikely(ZERO_OR_NULL_PTR(objp)) || !__kasan_check_read(objp, 1))
return 0;

size = __ksize(objp);
_