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-rw-r--r--Documentation/00-INDEX2
-rw-r--r--Documentation/namespaces/compatibility-list.txt39
2 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index 299615d821ac..c3014df066c4 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -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/
diff --git a/Documentation/namespaces/compatibility-list.txt b/Documentation/namespaces/compatibility-list.txt
new file mode 100644
index 000000000000..defc5589bfcd
--- /dev/null
+++ b/Documentation/namespaces/compatibility-list.txt
@@ -0,0 +1,39 @@
+ 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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