1 files changed, 21 insertions, 1 deletions
diff --git a/mm/slab_common.c b/mm/slab_common.c
index b7c6a40e436a..a09bb10aa026 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1613,7 +1613,27 @@ EXPORT_SYMBOL(kzfree);
  */
 size_t ksize(const void *objp)
 {
-	size_t size = __ksize(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
+	 * generate a more useful report at the time ksize() is called (rather
+	 * than later where behaviour is undefined due to potential
+	 * use-after-free or double-free).
+	 *
+	 * If the pointed to memory is invalid we return 0, to avoid users of
+	 * ksize() writing to and potentially corrupting the memory region.
+	 *
+	 * 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))
+		return 0;
+
+	size = __ksize(objp);
 	/*
 	 * We assume that ksize callers could use whole allocated area,
 	 * so we need to unpoison this area.