[PATCH v2 4/6] mm: Use overflow helpers in kmalloc_array*()

[Kees Cook <keescook@xxxxxxxxxxxx>]

Instead of open-coded multiplication and bounds checking, use the new
overflow helper.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/slab.h | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 81ebd71f8c03..4d759e1ddc33 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -13,6 +13,7 @@
 #define	_LINUX_SLAB_H
 
 #include <linux/gfp.h>
+#include <linux/overflow.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
@@ -624,11 +625,13 @@ int memcg_update_all_caches(int num_memcgs);
  */
 static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
 {
-	if (size != 0 && n > SIZE_MAX / size)
+	size_t bytes;
+
+	if (unlikely(check_mul_overflow(n, size, &bytes)))
 		return NULL;
 	if (__builtin_constant_p(n) && __builtin_constant_p(size))
-		return kmalloc(n * size, flags);
-	return __kmalloc(n * size, flags);
+		return kmalloc(bytes, flags);
+	return __kmalloc(bytes, flags);
 }
 
 /**
@@ -657,11 +660,13 @@ extern void *__kmalloc_track_caller(size_t, gfp_t, unsigned long);
 static inline void *kmalloc_array_node(size_t n, size_t size, gfp_t flags,
 				       int node)
 {
-	if (size != 0 && n > SIZE_MAX / size)
+	size_t bytes;
+
+	if (unlikely(check_mul_overflow(n, size, &bytes)))
 		return NULL;
 	if (__builtin_constant_p(n) && __builtin_constant_p(size))
-		return kmalloc_node(n * size, flags, node);
-	return __kmalloc_node(n * size, flags, node);
+		return kmalloc_node(bytes, flags, node);
+	return __kmalloc_node(bytes, flags, node);
 }
 
 static inline void *kcalloc_node(size_t n, size_t size, gfp_t flags, int node)
-- 
2.17.0