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From: Seth Forshee <seth.forshee@canonical.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linux Containers <containers@lists.linux-foundation.org>,
	linux-fsdevel@vger.kernel.org,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Christian Brauner <christian@brauner.io>,
	linux-kernel@vger.kernel.org
Subject: Re: [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on owned filesystems.
Date: Thu, 24 May 2018 08:55:17 -0500	[thread overview]
Message-ID: <20180524135517.GQ3401@ubuntu-xps13> (raw)
In-Reply-To: <20180523232538.4880-2-ebiederm@xmission.com>

On Wed, May 23, 2018 at 06:25:34PM -0500, Eric W. Biederman wrote:
> These filesystems already always set SB_I_NODEV so mknod will not be
> useful for gaining control of any devices no matter their permissions.
> This will allow overlayfs and applications to fakeroot to use device
> nodes to represent things on disk.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

For a normal filesystem this does seem safe enough.

However, I'd also like to see us allow unprivileged mounting for
overlayfs, and there we need to worry about whether this would allow a
mknod in an underlying filesystem which should not be allowed. That
mknod will be subject to this same check in the underlying filesystem
using the credentials of the user that mounted the overaly fs, which
should be sufficient to ensure that the mknod is permitted.

Thus this looks okay to me.

Acked-by: Seth Forshee <seth.forshee@canonical.com>

  reply	other threads:[~2018-05-24 13:55 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-23 23:22 [REVIEW][PATCH 0/6] Wrapping up the vfs support for unprivileged mounts Eric W. Biederman
2018-05-23 23:25 ` [REVIEW][PATCH 1/6] vfs: Don't allow changing the link count of an inode with an invalid uid or gid Eric W. Biederman
2018-05-24 12:58   ` Seth Forshee
2018-05-24 22:30     ` Christian Brauner
2018-05-23 23:25 ` [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on owned filesystems Eric W. Biederman
2018-05-24 13:55   ` Seth Forshee [this message]
2018-05-24 16:55     ` Eric W. Biederman
2018-05-24 17:22       ` Seth Forshee
2018-05-24 19:12   ` Christian Brauner
2018-05-23 23:25 ` [REVIEW][PATCH 3/6] fs: Allow superblock owner to replace invalid owners of inodes Eric W. Biederman
2018-05-23 23:41   ` [REVIEW][PATCH v2 " Eric W. Biederman
2018-05-24 22:30     ` Christian Brauner
2018-05-23 23:25 ` [REVIEW][PATCH 4/6] fs: Allow superblock owner to access do_remount_sb() Eric W. Biederman
2018-05-24 15:58   ` Christian Brauner
2018-05-24 16:45     ` Eric W. Biederman
2018-05-24 17:28       ` Christian Brauner
2018-05-23 23:25 ` [REVIEW][PATCH 5/6] capabilities: Allow privileged user in s_user_ns to set security.* xattrs Eric W. Biederman
2018-05-24 15:57   ` Christian Brauner
2018-05-23 23:25 ` [REVIEW][PATCH 6/6] fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems Eric W. Biederman
2018-05-24 15:59   ` Christian Brauner
2018-05-24 21:46 ` [REVIEW][PATCH 0/6] Wrapping up the vfs support for unprivileged mounts Theodore Y. Ts'o
2018-05-24 23:23   ` Eric W. Biederman
2018-05-25  3:57     ` Dave Chinner
2018-05-25  4:06       ` Darrick J. Wong
2018-05-29 13:12       ` Eric W. Biederman
2018-05-29 22:17         ` Dave Chinner
2018-05-30  2:34           ` Eric W. Biederman
2018-05-30  4:34             ` Dave Chinner
2018-05-29 15:40 ` Dongsu Park

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