nilfs2: fix link count underflow when removing corrupted directory

When removing an empty directory with a corrupted link count (e.g.,
i_nlink is 1 due to filesystem corruption), nilfs_rmdir() calls
drop_nlink() via nilfs_do_unlink() and then calls drop_nlink() again
on the directory inode.  This second call causes an underflow of
i_nlink, triggering a kernel WARNING in drop_nlink().

Fix this issue by using clear_nlink() instead of drop_nlink() to
finalize the link count reset for the target directory in nilfs_rmdir().
Additionally, log a warning message when i_nlink is not 2 before
removing an empty directory to notify about the link count inconsistency.

Reported-by: syzbot+c388db0347b7fc88fa7a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c388db0347b7fc88fa7a
Fixes: d25006523d0b ("nilfs2: pathname operations")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

0 files changed, 0 insertions, 0 deletions