[PATCH v2 00/10] userns: sysctl limits for namespaces

From: Eric W. Biederman
Date: Thu Jul 21 2016 - 12:52:44 EST

This patchset addresses two use cases:
- Implement a sane upper bound on the number of namespaces.
- Provide a way for sandboxes to limit the attack surface from

The maximum sane case I can imagine is if every process is a fat
process, so I set the maximum number of namespaces to the maximum
number of threads.

I make these limits recursive and per user namespace so that a
usernamespace root can reduce the limits further. If a user namespace
root raises the limit the limit in the parent namespace will be honored.

I have cut this implementation to the bare minimum needed to achieve
these objectives.

Does anyone know if there is a proper error code to return for resource
limit exceeded? I am currently using -EUSERS or -ENFILE but both of
those feel a little wrong.

Assuming nothing problematic shows up in the review I will add these to
my user namespace tree.

These patches are also available at:
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-testing

Changes since v1:
- Compilation issues with !CONFIG_SYSCTL and !CONFIG_USER_NS have been addressed
- Comment improvements.
- A few names have been changed to be clearer.

Eric W. Biederman (10):
sysctl: Stop implicitly passing current into sysctl_table_root.lookup
userns: Add per user namespace sysctls.
userns: Add a limit on the number of user namespaces
userns: Generalize the user namespace count into ucount
pidns: Add a limit on the number of pid namespaces
utsns: Add a limit on the number of uts namespaces
ipcns: Add a limit on the number of ipc namespaces
cgroupns: Add a limit on the number of cgroup namespaces
netns: Add a limit on the number of net namespaces
mntns: Add a limit on the number of mount namespaces.

fs/namespace.c | 19 ++++-
fs/proc/proc_sysctl.c | 14 +--
include/linux/sysctl.h | 3 +-
include/linux/user_namespace.h | 40 +++++++++
ipc/namespace.c | 42 ++++++---
kernel/cgroup.c | 15 ++++
kernel/fork.c | 5 ++
kernel/pid_namespace.c | 22 ++++-
kernel/user_namespace.c | 188 ++++++++++++++++++++++++++++++++++++++---
kernel/utsname.c | 31 +++++--
net/core/net_namespace.c | 15 ++++
net/sysctl_net.c | 4 +-
12 files changed, 355 insertions(+), 43 deletions(-)