mm/z3fold: avoid possible underflow in z3fold_alloc()

It is not enough to just make sure the z3fold header is not larger than the page size. When z3fold header is equal to PAGE_SIZE, we would underflow when check alloc size against PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE in z3fold_alloc(). Make sure there has remaining spaces for its buddy to fix this theoretical issue. Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Miaohe Lin <[email protected]> Reviewed-by: Vitaly Wool <[email protected]> Cc: Hillf Danton <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
niw · Jul 1, 2021 · 014284a · 014284a
1 parent e3c0db4
commit 014284a
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/mm/z3fold.c b/mm/z3fold.c
@@ -1803,8 +1803,11 @@ static int __init init_z3fold(void)
 {
 	int ret;
 
-	/* Make sure the z3fold header is not larger than the page size */
-	BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
+	/*
+	 * Make sure the z3fold header is not larger than the page size and
+	 * there has remaining spaces for its buddy.
+	 */
+	BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
 	ret = z3fold_mount();
 	if (ret)
 		return ret;