linux-kernel - Re: [PATCH 2/2] ovl: allow distributed fs as lower layer

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Message-ID: <CAJfpegtM4KnKA+isDTDpakJcaYJT5nhN=pQUJx8Hs58SsondJA@mail.gmail.com>
Date:	Tue, 9 Jun 2015 14:44:09 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	sa <sa-dev@...nbow.by>, "Roth, Andre" <andre.roth@...he.com>
Subject: Re: [PATCH 2/2] ovl: allow distributed fs as lower layer

On Sun, Jun 7, 2015 at 3:02 AM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> A nasty corner case to be aware of (and I think this is part of what Al
> was warning about).  /proc/sys/net is different depending upon which
> current->nsproxy->net_ns.

Ah,  I'm beginning to grasp what's going on there: mulitple dentries
with the same name but belonging to different namespaces,
->d_compare() being used to select the right one.  Is that it?

Overlayfs checks for d_compare() on the root of the lower and upper
trees, but here it only set on a subdirectory of proc, not on every
dentry.  So overlayfs should be careful and check for
DCACHE_OP_COMPARE | DCACHE_OP_HASH and reject going down such a
dentry.


Thanks,
Miklos
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