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

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Date:	Mon,  1 Feb 2016 23:36:52 +0800
From:	Rui Wang <rui.y.wang@...el.com>
To:	koct9i@...il.com
Cc:	rui.y.wang@...el.com, miklos@...redi.hu, viro@...iv.linux.org.uk,
	linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, vgoyal@...hat.com
Subject: Re: [PATCH] ovl: fix getcwd() failure after unsuccessful rmdir

On Sat, Jan 30, 2016 5:44 PM Konstantin Khlebnikov <koct9i@...il.com> wrote: 
> 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.

Yes I had the same feeling. There's a "goto out_d_drop" which causes
d_drop() to be called if ovl_do_rename() fails. but I wasn't able to
find a way to reproduce this problem, so I only fixed the problem
described in bug110491. It's what I could reliably test.

Thanks
Rui