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Message-ID: <20201102175526.eu4npm4v2ggicvaf@wittgenstein>
Date: Mon, 2 Nov 2020 18:55:26 +0100
From: Christian Brauner <christian.brauner@...ntu.com>
To: Alexey Gladkov <gladkov.alexey@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Linux Containers <containers@...ts.linux-foundation.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Alexey Gladkov <legion@...nel.org>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Kees Cook <keescook@...omium.org>,
Christian Brauner <christian@...uner.io>
Subject: Re: [RFC PATCH v1 0/4] Per user namespace rlimits
On Mon, Nov 02, 2020 at 05:50:29PM +0100, Alexey Gladkov wrote:
> Preface
> -------
> These patches are for binding the rlimits to a user in the user namespace.
> This patch set can be applied on top of:
>
> git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v5.8-2-g43e210d68200
>
> Problem
> -------
> Some rlimits are set per user: RLIMIT_NPROC, RLIMIT_MEMLOCK, RLIMIT_SIGPENDING,
> RLIMIT_MSGQUEUE. When several containers are created from one user then
> the processes inside the containers influence each other.
>
> Eric W. Biederman mentioned this issue [1][2][3].
>
> Introduced changes
> ------------------
> To fix this problem, you can bind the counter of the specified rlimits to the
> user within the user namespace. By default, to preserve backward compatibility,
> only the initial user namespace is used. This patch adds one more prctl
> parameter to change the binding to the user namespace.
>
> This will not cause the user to take more resources than allowed in the parent
> user namespace because it only virtualizes the rlimit counter. Limits in all
> parent user namespaces are taken into account.
>
> For example, this allows us to run multiple containers by the same user and
> set the RLIMIT_NPROC to 1 inside.
Thanks for picking this up and working on it. This would definitely fix
many issues for folks running unprivileged containers using a single id
map which is the default behavior for LXC/LXD and so very valuable to
us.
Christian
>
> ToDo
> ----
> * RLIMIT_MEMLOCK, RLIMIT_SIGPENDING and RLIMIT_MSGQUEUE are not implemented.
> * No documentation.
> * No tests.
>
> [1] https://lore.kernel.org/containers/87imd2incs.fsf@x220.int.ebiederm.org/
> [2] https://lists.linuxfoundation.org/pipermail/containers/2020-August/042096.html
> [3] https://lists.linuxfoundation.org/pipermail/containers/2020-October/042524.html
>
> Changelog
> ---------
> v1:
> * After discussion with Eric W. Biederman, I increased the size of ucounts to
> atomic_long_t.
> * Added ucount_max to avoid the fork bomb.
>
> --
>
> Alexey Gladkov (4):
> Increase size of ucounts to atomic_long_t
> Move the user's process counter to ucounts
> Do not allow fork if RLIMIT_NPROC is exceeded in the user namespace
> tree
> Allow to change the user namespace in which user rlimits are counted
>
> fs/exec.c | 13 ++++++---
> fs/io-wq.c | 25 +++++++++++++-----
> fs/io-wq.h | 1 +
> fs/io_uring.c | 1 +
> include/linux/cred.h | 8 ++++++
> include/linux/sched.h | 3 +++
> include/linux/sched/user.h | 1 -
> include/linux/user_namespace.h | 12 +++++++--
> include/uapi/linux/prctl.h | 5 ++++
> kernel/cred.c | 44 ++++++++++++++++++++++++-------
> kernel/exit.c | 2 +-
> kernel/fork.c | 13 ++++++---
> kernel/sys.c | 26 ++++++++++++++++--
> kernel/ucount.c | 48 +++++++++++++++++++++++++++++-----
> kernel/user.c | 3 ++-
> kernel/user_namespace.c | 3 +++
> 16 files changed, 171 insertions(+), 37 deletions(-)
>
> --
> 2.25.4
>
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