[PATCH AUTOSEL 6.1 08/15] erofs: ensure m_llen is reset to 0 if metadata is invalid

[Sasha Levin <sashal@kernel.org>]

From: Gao Xiang <hsiangkao@linux.alibaba.com>

[ Upstream commit 9b32b063be1001e322c5f6e01f2a649636947851 ]

Sometimes, the on-disk metadata might be invalid due to user
interrupts, storage failures, or other unknown causes.

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.

Link: https://lore.kernel.org/r/20240629185743.2819229-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/erofs/zmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index abcded1acd194..4864863cd1298 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -763,6 +763,8 @@ 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);
 
 	/* aggressively BUG_ON iff CONFIG_EROFS_FS_DEBUG is on */
-- 
2.43.0