From: Jan Kara
> Sent: 23 May 2023 14:14
>
> Commit 0813299c586b ("ext4: Fix possible corruption when moving a
> directory") forgot that handling of RENAME_EXCHANGE renames needs the
> protection of inode lock when changing directory parents for moved
> directories. Add proper locking for that case as well.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: 0813299c586b ("ext4: Fix possible corruption when moving a directory")
> Reported-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/ext4/namei.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 45b579805c95..b91abea1c781 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -4083,10 +4083,25 @@ static int ext4_cross_rename(struct inode *old_dir, struct dentry *old_dentry,
> if (retval)
> return retval;
>
> + /*
> + * We need to protect against old.inode and new.inode directory getting
> + * converted from inline directory format into a normal one. The lock
> + * ordering does not matter here as old and new are guaranteed to be
> + * incomparable in the directory hierarchy.
> + */
> + if (S_ISDIR(old.inode->i_mode))
> + inode_lock(old.inode);
> + if (S_ISDIR(new.inode->i_mode))
> + inode_lock_nested(new.inode, I_MUTEX_NONDIR2);
> +
What happens if there is another concurrent rename from new.inode
to old.inode?
That will try to acquire the locks in the other order.
David
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