diff options
Diffstat (limited to 'Documentation/namespaces')
| -rw-r--r-- | Documentation/namespaces/compatibility-list.txt | 39 | ||||
| -rw-r--r-- | Documentation/namespaces/resource-control.txt | 14 |
2 files changed, 53 insertions, 0 deletions
diff --git a/Documentation/namespaces/compatibility-list.txt b/Documentation/namespaces/compatibility-list.txt new file mode 100644 index 000000000..defc5589b --- /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. + diff --git a/Documentation/namespaces/resource-control.txt b/Documentation/namespaces/resource-control.txt new file mode 100644 index 000000000..abc13c394 --- /dev/null +++ b/Documentation/namespaces/resource-control.txt @@ -0,0 +1,14 @@ +There are a lot of kinds of objects in the kernel that don't have +individual limits or that have limits that are ineffective when a set +of processes is allowed to switch user ids. With user namespaces +enabled in a kernel for people who don't trust their users or their +users programs to play nice this problems becomes more acute. + +Therefore it is recommended that memory control groups be enabled in +kernels that enable user namespaces, and it is further recommended +that userspace configure memory control groups to limit how much +memory user's they don't trust to play nice can use. + +Memory control groups can be configured by installing the libcgroup +package present on most distros editing /etc/cgrules.conf, +/etc/cgconfig.conf and setting up libpam-cgroup. |