linux-kernel - Re: [PATCH] ovl: fix getcwd() failure after unsuccessful rmdir

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Date:	Sat, 30 Jan 2016 12:44:14 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Rui Wang <rui.y.wang@...el.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-unionfs@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] ovl: fix getcwd() failure after unsuccessful rmdir

On Fri, Jan 8, 2016 at 6:09 PM, Rui Wang <rui.y.wang@...el.com> wrote:
> ovl_remove_upper() should do d_drop() only after it successfully
> removes the dir, otherwise a subsequent getcwd() system call will
> fail, breaking userspace programs.
>
> This is to fix: https://bugzilla.kernel.org/show_bug.cgi?id=110491
>
> Signed-off-by: Rui Wang <rui.y.wang@...el.com>

Reviewed-by: Konstantin Khlebnikov <koct9i@...il.com>

The same problem also in ovl_remove_and_whiteout() - when we
remove non-pure dentry. It checks that directory isn't empty before,
but I'm sure that vfs_rename which exchanges dentry and whiteout
could fail for some reason and we'll end with unhashed dentry when
nothing actually has been changed.

> ---
>  fs/overlayfs/dir.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 692ceda..36d6a5b 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -618,7 +618,8 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
>          * sole user of this dentry.  Too tricky...  Just unhash for
>          * now.
>          */
> -       d_drop(dentry);
> +       if (!err)
> +               d_drop(dentry);
>         mutex_unlock(&dir->i_mutex);
>
>         return err;
> --
> 1.7.5.4
>