Re: [PATCH] ext4: Fix possible corruption when moving a directory

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Jan 26, 2023 at 12:22:21PM +0100, Jan Kara wrote:
> When we are renaming a directory to a different directory, we need to
> update '..' entry in the moved directory. However nothing prevents moved
> directory from being modified and even converted from the inline format
> to the normal format. When such race happens the rename code gets
> confused and we crash. Fix the problem by locking the moved directory.

Four months later, I have a question --

Is it necessary for ext4_cross_rename to inode_lock_nested on both
old.inode and new.inode?  We're resetting the dotdot entries on both
children in that case, which means that we also need to lock out inline
data conversions, right?

--D

> CC: stable@vger.kernel.org
> Fixes: 32f7f22c0b52 ("ext4: let ext4_rename handle inline dir")
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/ext4/namei.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index dd28453d6ea3..270fbcba75b6 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -3872,9 +3872,16 @@ static int ext4_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
>  			if (new.dir != old.dir && EXT4_DIR_LINK_MAX(new.dir))
>  				goto end_rename;
>  		}
> +		/*
> +		 * We need to protect against old.inode directory getting
> +		 * converted from inline directory format into a normal one.
> +		 */
> +		inode_lock_nested(old.inode, I_MUTEX_NONDIR2);
>  		retval = ext4_rename_dir_prepare(handle, &old);
> -		if (retval)
> +		if (retval) {
> +			inode_unlock(old.inode);
>  			goto end_rename;
> +		}
>  	}
>  	/*
>  	 * If we're renaming a file within an inline_data dir and adding or
> @@ -4006,6 +4013,8 @@ static int ext4_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
>  	} else {
>  		ext4_journal_stop(handle);
>  	}
> +	if (old.dir_bh)
> +		inode_unlock(old.inode);
>  release_bh:
>  	brelse(old.dir_bh);
>  	brelse(old.bh);
> -- 
> 2.35.3
>