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

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Message-ID: <CAJfpegsowAwXL6hWZMa_d3Jwc=unPnDo2A-uQgyoDDw=h9Szqw@mail.gmail.com>
Date:	Wed, 2 Mar 2016 15:17:24 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Rui Wang <rui.y.wang@...el.com>
Cc:	Konstantin Khlebnikov <koct9i@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
	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 Mon, Feb 1, 2016 at 4:36 PM, Rui Wang <rui.y.wang@...el.com> wrote:
> 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 for the patch.  Added to the queue.

Miklos