[PATCH] nilfs2: fix NULL pointer dereference at nilfs_bmap_lookup_at_level()

[Ryusuke Konishi]

If the i_mode field in inode of metadata files is corrupted on disk,
it can cause the initialization of bmap structure, which should have
been called from nilfs_read_inode_common(), not to be called.  This
causes a lockdep warning followed by a NULL pointer dereference at
nilfs_bmap_lookup_at_level().

This patch fixes these issues by adding a missing sanitiy check for
the i_mode field of metadata file's inode.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Reported-by: syzbot+2b32eb36c1a825b7a74c@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 fs/nilfs2/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 67f63cfeade5..d4e653d51869 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -440,6 +440,8 @@ int nilfs_read_inode_common(struct inode *inode,
 	inode->i_atime.tv_nsec = le32_to_cpu(raw_inode->i_mtime_nsec);
 	inode->i_ctime.tv_nsec = le32_to_cpu(raw_inode->i_ctime_nsec);
 	inode->i_mtime.tv_nsec = le32_to_cpu(raw_inode->i_mtime_nsec);
+	if (nilfs_is_metadata_file_inode(inode) && !S_ISREG(inode->i_mode))
+		return -EIO; /* this inode is for metadata and corrupted */
 	if (inode->i_nlink == 0)
 		return -ESTALE; /* this inode is deleted */
 
-- 
2.34.1