Preface ------- These patches are for binding the rlimit counters to a user in user namespace. This patch set can be applied on top of: git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v5.11-rc2 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]. For example, there are two containers (A and B) created by one user. The container A sets RLIMIT_NPROC=1 and starts one process. Everything is fine, but when container B tries to do the same it will fail because the number of processes is counted globally for each user and user has one process already. On the other hand, we cannot simply calculate the rlimits for each container separately. This will lead to the fact that the user creating a new user namespace can create a fork bomb. Introduced changes ------------------ To address the problem, we bind rlimit counters to each user namespace. The result is a tree of rlimit counters with the biggest value at the root (aka init_user_ns). The rlimit counter increment/decrement occurs in the current and all parent user namespaces. ToDo ---- * No documentation. * No tests. [1] https://lore.kernel.org/containers/87imd2incs.fsf@xxxxxxxxxxxxxxxxxxxxx/ [2] https://lists.linuxfoundation.org/pipermail/containers/2020-August/042096.html [3] https://lists.linuxfoundation.org/pipermail/containers/2020-October/042524.html Changelog --------- v2: * RLIMIT_MEMLOCK, RLIMIT_SIGPENDING and RLIMIT_MSGQUEUE are migrated to ucounts. * Added ucounts for pair uid and user namespace into cred. * Added the ability to increase ucount by more than 1. 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 (8): Use atomic type for ucounts reference counting Add a reference to ucounts for each user Increase size of ucounts to atomic_long_t Move RLIMIT_NPROC counter to ucounts Move RLIMIT_MSGQUEUE counter to ucounts Move RLIMIT_SIGPENDING counter to ucounts Move RLIMIT_MEMLOCK counter to ucounts Move RLIMIT_NPROC check to the place where we increment the counter fs/exec.c | 2 +- fs/hugetlbfs/inode.c | 17 +++--- fs/io-wq.c | 22 ++++---- fs/io-wq.h | 2 +- fs/io_uring.c | 2 +- fs/proc/array.c | 2 +- include/linux/cred.h | 3 ++ include/linux/hugetlb.h | 3 +- include/linux/mm.h | 4 +- include/linux/sched/user.h | 6 --- include/linux/shmem_fs.h | 2 +- include/linux/signal_types.h | 4 +- include/linux/user_namespace.h | 31 +++++++++-- ipc/mqueue.c | 29 +++++----- ipc/shm.c | 31 ++++++----- kernel/cred.c | 43 +++++++++++---- kernel/exit.c | 2 +- kernel/fork.c | 12 +++-- kernel/signal.c | 53 ++++++++---------- kernel/sys.c | 13 ----- kernel/ucount.c | 99 +++++++++++++++++++++++++++++----- kernel/user.c | 2 - kernel/user_namespace.c | 7 ++- mm/memfd.c | 4 +- mm/mlock.c | 35 +++++------- mm/mmap.c | 3 +- mm/shmem.c | 8 +-- 27 files changed, 268 insertions(+), 173 deletions(-) -- 2.29.2
