[PATCH v2 5/6] mm: Use overflow helpers in kvmalloc()

[Kees Cook <keescook@xxxxxxxxxxxx>]

Instead of open-coded multiplication and bounds checking, use the new
overflow helper. Additionally prepare for vmalloc() users to add
array_size()-family helpers in the future.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/mm.h      | 7 +++++--
 include/linux/vmalloc.h | 1 +
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1ac1f06a4be6..7cb1c6a6bf82 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -25,6 +25,7 @@
 #include <linux/err.h>
 #include <linux/page_ref.h>
 #include <linux/memremap.h>
+#include <linux/overflow.h>
 
 struct mempolicy;
 struct anon_vma;
@@ -560,10 +561,12 @@ static inline void *kvzalloc(size_t size, gfp_t flags)
 
 static inline void *kvmalloc_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;
 
-	return kvmalloc(n * size, flags);
+	return kvmalloc(bytes, flags);
 }
 
 extern void kvfree(const void *addr);
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 1e5d8c392f15..398e9c95cd61 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -8,6 +8,7 @@
 #include <linux/llist.h>
 #include <asm/page.h>		/* pgprot_t */
 #include <linux/rbtree.h>
+#include <linux/overflow.h>
 
 struct vm_area_struct;		/* vma defining user mapping in mm_types.h */
 struct notifier_block;		/* in notifier.h */
-- 
2.17.0