linux-kernel - Re: Mount namespace "dominant peer group"?

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Message-ID: <CAOssrKfmDEP3T6qpiAT5m4Y1CfzRPfzUt6ST2rcS+j0qek+mzw@mail.gmail.com>
Date:	Mon, 23 May 2016 09:55:35 +0200
From:	Miklos Szeredi <mszeredi@...hat.com>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	Ram Pai <linuxram@...ibm.com>, lkml <linux-kernel@...r.kernel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: Mount namespace "dominant peer group"?

C is slave of B is slave of A.  If a process can see (i.e. has under
its root) A and C but not B then for C it will show
master:B,propagate_from:A.  This piece of information is shown because
it can't see the immediate master (B) and so cannot determine the
chain of propagation between the mounts it can see.

Concrete example:

# mount --bind / /mnt
# mount --bind /proc /mnt/proc
# mount --make-private /mnt
# mount --make-shared /mnt
# mkdir /tmp/etc
# mount --bind /mnt/etc /tmp/etc
# mount --make-slave /tmp/etc
# mount --make-shared /tmp/etc
# mount --bind /tmp/etc /mnt/tmp/etc
# mount --make-slave /mnt/tmp/etc
# cat /proc/self/mountinfo | grep /tmp/etc
164 40 253:1 /etc /tmp/etc rw,relatime shared:100 master:97 - ...
# chroot /mnt
# cat /proc/self/mountinfo
129 62 253:1 / / rw,relatime shared:97 - ...
168 129 253:1 /etc /tmp/etc rw,relatime master:100 propagate_from:97 - ...

Thanks,
Miklos