linux-kernel - [PATCH] mm: ksize() should silently accept a NULL pointer

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Date:   Tue, 16 Jun 2020 16:54:09 -0600
From:   William Kucharski <william.kucharski@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] 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.

Signed-off-by: William Kucharski <william.kucharski@...cle.com>
---
 mm/slab_common.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 9e72ba224175..2bff01ad94d8 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1660,10 +1660,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 					   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);
@@ -1723,10 +1722,9 @@ void kzfree(const void *p)
 	size_t ks;
 	void *mem = (void *)p;
 
-	if (unlikely(ZERO_OR_NULL_PTR(mem)))
-		return;
 	ks = ksize(mem);
-	memset(mem, 0, ks);
+	if (ks)
+		memset(mem, 0, ks);
 	kfree(mem);
 }
 EXPORT_SYMBOL(kzfree);
@@ -1749,8 +1747,6 @@ 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
@@ -1764,7 +1760,7 @@ 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);
-- 
2.26.2