linux-kernel - [PATCH] erofs: ensure m_llen is reset to 0 if metadata is invalid

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Date: Sun, 30 Jun 2024 02:57:43 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: linux-erofs@...ts.ozlabs.org,
	Chao Yu <chao@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Gao Xiang <hsiangkao@...ux.alibaba.com>
Subject: [PATCH] erofs: ensure m_llen is reset to 0 if metadata is invalid

Sometimes, the on-disk metadata might be invalid due to storage
failure or other unknown issues.

In that case, z_erofs_map_blocks_iter() may still return a valid
m_llen while other fields remain invalid (e.g., m_plen can be 0).

Due to the return value of z_erofs_scan_folio() in some path will
be ignored on purpose, the following z_erofs_scan_folio() could
then use the invalid value by accident.

Let's reset m_llen to 0 to prevent this.

Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
---
 fs/erofs/zmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index 9b248ee5fef2..74d3d7bffcf3 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -711,6 +711,8 @@ int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,

 	err = z_erofs_do_map_blocks(inode, map, flags);
 out:
+	if (err)
+		map->m_llen = 0;
 	trace_z_erofs_map_blocks_iter_exit(inode, map, flags, err);
 	return err;
 }
-- 
2.43.5