[061/192] mm/z3fold: avoid possible underflow in z3fold_alloc()

Commit Message

Andrew Morton July 1, 2021, 1:50 a.m. UTC

From: Miaohe Lin <[e-mail]>
Subject: 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/[e-mail]
Signed-off-by: Miaohe Lin <[e-mail]>
Reviewed-by: Vitaly Wool <[e-mail]>
Cc: Hillf Danton <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/z3fold.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Patch

--- a/mm/z3fold.c~mm-z3fold-avoid-possible-underflow-in-z3fold_alloc
+++ a/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;