Commit 2868f89f authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by Linus Torvalds

The namespaces compatibility list doc

People discuss how the namespaces are working/going-to-work together.

Ted Ts'o proposed to create some document that describes what problems user
may have when he/she creates some new namespace, but keeps others shared.
I liked this idea, so here's the initial version of such a document with
the problems I currently have in mind and can describe somewhat audibly -
the "namespaces compatibility list".

The Documentation/namespaces/ directory is about to contain more docs about
the namespaces stuff.

Thanks to Cedirc for notes and spell checks on the doc, to Daniel for
additional info about IPC and User namespaces interaction and to Randy, who
alluded me to using a spell checker before sending the documentation :)
Signed-off-by: default avatarPavel Emelyanov <xemul@openvz.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Daniel Lezcano <dlezcano@fr.ibm.com>
Cc: Theodore Tso <tytso@mit.edu>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 32df81cb
......@@ -262,6 +262,8 @@ mtrr.txt
- how to use PPro Memory Type Range Registers to increase performance.
mutex-design.txt
- info on the generic mutex subsystem.
namespaces/
- directory with various information about namespaces
nbd.txt
- info on a TCP implementation of a network block device.
netlabel/
......
Namespaces compatibility list
This document contains the information about the problems user
may have when creating tasks living in different namespaces.
Here's the summary. This matrix shows the known problems, that
occur when tasks share some namespace (the columns) while living
in different other namespaces (the rows):
UTS IPC VFS PID User Net
UTS X
IPC X 1
VFS X
PID 1 1 X
User 2 2 X
Net X
1. Both the IPC and the PID namespaces provide IDs to address
object inside the kernel. E.g. semaphore with IPCID or
process group with pid.
In both cases, tasks shouldn't try exposing this ID to some
other task living in a different namespace via a shared filesystem
or IPC shmem/message. The fact is that this ID is only valid
within the namespace it was obtained in and may refer to some
other object in another namespace.
2. Intentionally, two equal user IDs in different user namespaces
should not be equal from the VFS point of view. In other
words, user 10 in one user namespace shouldn't have the same
access permissions to files, belonging to user 10 in another
namespace.
The same is true for the IPC namespaces being shared - two users
from different user namespaces should not access the same IPC objects
even having equal UIDs.
But currently this is not so.
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