Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) client-ip=23.128.96.34;
From:   Sergey Shtylyov <s.shtylyov@omp.ru>
To:     Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
CC:     <linux-kernel@vger.kernel.org>
Subject: [PATCH] f2fs: data: fix possible overflow in check_swap_activate()
Date:   Wed, 25 Oct 2023 23:20:19 +0300
Message-ID: <20231025202019.5228-1-s.shtylyov@omp.ru>
MIME-Version: 1.0
Content-Transfer-Encoding: 7BIT
Content-Type:   text/plain; charset=US-ASCII
X-KSE-Attachment-Filter-Triggered-Filters: Clean
X-KSE-BulkMessagesFiltering-Scan-Result: InTheLimit
X-Spam-Status: No, score=2.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,RCVD_IN_SBL_CSS,SPF_HELO_NONE,SPF_PASS autolearn=no
	autolearn_force=no version=3.4.6
X-Spam-Level: **
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on howler.vger.email
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (howler.vger.email [0.0.0.0]); Wed, 25 Oct 2023 13:20:58 -0700 (PDT)

In check_swap_activate(), if the *while* loop exits early (0- or 1-page
long swap file), an overflow happens while calculating the value of the
span parameter as the lowest_pblock variable ends up being greater than
the highest_pblock variable. Let's set *span to 0 in this case...

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
---
This patch is against the 'master' branch of Jaegeuk Kim's F2FS repo...

 fs/f2fs/data.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 916e317ac925..342cb0d5056d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -4047,7 +4047,10 @@ static int check_swap_activate(struct swap_info_struct *sis,
 		cur_lblock += nr_pblocks;
 	}
 	ret = nr_extents;
-	*span = 1 + highest_pblock - lowest_pblock;
+	if (lowest_pblock <= highest_pblock)
+		*span = 1 + highest_pblock - lowest_pblock;
+	else
+		*span = 0;
 	if (cur_lblock == 0)
 		cur_lblock = 1;	/* force Empty message */
 	sis->max = cur_lblock;
-- 
2.26.3