linux/Documentation/namespaces/compatibility-list.txt
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   1        Namespaces compatibility list
   2
   3This document contains the information about the problems user
   4may have when creating tasks living in different namespaces.
   5
   6Here's the summary. This matrix shows the known problems, that
   7occur when tasks share some namespace (the columns) while living
   8in different other namespaces (the rows):
   9
  10        UTS     IPC     VFS     PID     User    Net
  11UTS      X
  12IPC              X       1
  13VFS                      X
  14PID              1       1       X
  15User             2       2               X
  16Net                                              X
  17
  181. Both the IPC and the PID namespaces provide IDs to address
  19   object inside the kernel. E.g. semaphore with IPCID or
  20   process group with pid.
  21
  22   In both cases, tasks shouldn't try exposing this ID to some
  23   other task living in a different namespace via a shared filesystem
  24   or IPC shmem/message. The fact is that this ID is only valid
  25   within the namespace it was obtained in and may refer to some
  26   other object in another namespace.
  27
  282. Intentionally, two equal user IDs in different user namespaces
  29   should not be equal from the VFS point of view. In other
  30   words, user 10 in one user namespace shouldn't have the same
  31   access permissions to files, belonging to user 10 in another
  32   namespace.
  33
  34   The same is true for the IPC namespaces being shared - two users
  35   from different user namespaces should not access the same IPC objects
  36   even having equal UIDs.
  37
  38   But currently this is not so.
  39
  40
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