Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/ and make it readable

From: Pavel Emelyanov <xemul@parallels.com>
To: Kees Cook <keescook@chromium.org>, Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Calvin Owens <calvinowens@fb.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Peter Feiner <pfeiner@google.com>,
	Grant Likely <grant.likely@secretlab.ca>,
	Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
	Pavel Emelyanov <xemul@openvz.org>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/ and make it readable
Date: Wed, 28 Jan 2015 00:46:05 +0300	[thread overview]
Message-ID: <54C8071D.7030103@parallels.com> (raw)
In-Reply-To: <CAGXu5jJFFib7F7uKYgvX4ecyMnbincd22FaO_bFy=VRVKdFbvA@mail.gmail.com>

>>> Are mount namespaces handled in this output?
>>
>> Could you clarify this moment, i'm not sure i get it.
> 
> I changed how I asked this question in my review of the documentation,
> but it looks like these symlinks aren't "regular" symlinks (that are
> up to the follower to have access to the file system path shown), but
> rather they bypass VFS. As a result, I'm wondering how things like
> mount namespaces might change this behavior: what is shown, the path
> from the perspective of the target, or from the viewer (which may be
> in separate mount namespaces).

These work just like the /proc/$pid/fd/$n links do. When you readlink
on it the d_path() is called which walks up the dentry/vfsmnt tree
until it reaches either current root or the global one. For "another"
mount namespace case it produces the path relative to this namespace's
root.

Thanks,
Pavel