blackbird-op-linux/kernel/cgroup.c, branch v4.2

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2015-07-03T22:20:57+00:00

Pull user namespace updates from Eric Biederman: "Long ago and far away when user namespaces where young it was realized that allowing fresh mounts of proc and sysfs with only user namespace permissions could violate the basic rule that only root gets to decide if proc or sysfs should be mounted at all. Some hacks were put in place to reduce the worst of the damage could be done, and the common sense rule was adopted that fresh mounts of proc and sysfs should allow no more than bind mounts of proc and sysfs. Unfortunately that rule has not been fully enforced. There are two kinds of gaps in that enforcement. Only filesystems mounted on empty directories of proc and sysfs should be ignored but the test for empty directories was insufficient. So in my tree directories on proc, sysctl and sysfs that will always be empty are created specially. Every other technique is imperfect as an ordinary directory can have entries added even after a readdir returns and shows that the directory is empty. Special creation of directories for mount points makes the code in the kernel a smidge clearer about it's purpose. I asked container developers from the various container projects to help test this and no holes were found in the set of mount points on proc and sysfs that are created specially. This set of changes also starts enforcing the mount flags of fresh mounts of proc and sysfs are consistent with the existing mount of proc and sysfs. I expected this to be the boring part of the work but unfortunately unprivileged userspace winds up mounting fresh copies of proc and sysfs with noexec and nosuid clear when root set those flags on the previous mount of proc and sysfs. So for now only the atime, read-only and nodev attributes which userspace happens to keep consistent are enforced. Dealing with the noexec and nosuid attributes remains for another time. This set of changes also addresses an issue with how open file descriptors from /proc//ns/* are displayed. Recently readlink of /proc//fd has been triggering a WARN_ON that has not been meaningful since it was added (as all of the code in the kernel was converted) and is not now actively wrong. There is also a short list of issues that have not been fixed yet that I will mention briefly. It is possible to rename a directory from below to above a bind mount. At which point any directory pointers below the renamed directory can be walked up to the root directory of the filesystem. With user namespaces enabled a bind mount of the bind mount can be created allowing the user to pick a directory whose children they can rename to outside of the bind mount. This is challenging to fix and doubly so because all obvious solutions must touch code that is in the performance part of pathname resolution. As mentioned above there is also a question of how to ensure that developers by accident or with purpose do not introduce exectuable files on sysfs and proc and in doing so introduce security regressions in the current userspace that will not be immediately obvious and as such are likely to require breaking userspace in painful ways once they are recognized" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: vfs: Remove incorrect debugging WARN in prepend_path mnt: Update fs_fully_visible to test for permanently empty directories sysfs: Create mountpoints with sysfs_create_mount_point sysfs: Add support for permanently empty directories to serve as mount points. kernfs: Add support for always empty directories. proc: Allow creating permanently empty directories that serve as mount points sysctl: Allow creating permanently empty directories that serve as mountpoints. fs: Add helper functions for permanently empty directories. vfs: Ignore unlocked mounts in fs_fully_visible mnt: Modify fs_fully_visible to deal with locked ro nodev and atime mnt: Refactor the logic for mounting sysfs and proc in a user namespace

sysfs: Create mountpoints with sysfs_create_mount_point

2015-07-01T15:36:47+00:00

This allows for better documentation in the code and it allows for a simpler and fully correct version of fs_fully_visible to be written. The mount points converted and their filesystems are: /sys/hypervisor/s390/ s390_hypfs /sys/kernel/config/ configfs /sys/kernel/debug/ debugfs /sys/firmware/efi/efivars/ efivarfs /sys/fs/fuse/connections/ fusectl /sys/fs/pstore/ pstore /sys/kernel/tracing/ tracefs /sys/fs/cgroup/ cgroup /sys/kernel/security/ securityfs /sys/fs/selinux/ selinuxfs /sys/fs/smackfs/ smackfs Cc: stable@vger.kernel.org Acked-by: Greg Kroah-Hartman Signed-off-by: "Eric W. Biederman"

cgroup: require write perm on common ancestor when moving processes on the default hierarchy

2015-06-18T20:54:28+00:00

On traditional hierarchies, if a task has write access to "tasks" or "cgroup.procs" file of a cgroup and its euid agrees with the target, it can move the target to the cgroup; however, consider the following scenario. The owner of each cgroup is in the parentheses. R (root) - 0 (root) - 00 (user1) - 000 (user1) | \ 001 (user1) \ 1 (root) - 10 (user1) The subtrees of 00 and 10 are delegated to user1; however, while both subtrees may belong to the same user, it is clear that the two subtrees are to be isolated - they're under completely separate resource limits imposed by 0 and 1, respectively. Note that 0 and 1 aren't strictly necessary but added to ease illustrating the issue. If user1 is allowed to move processes between the two subtrees, the intention of the hierarchy - keeping a given group of processes under a subtree with certain resource restrictions while delegating management of the subtree - can be circumvented by user1. This happens because migration permission check doesn't consider the hierarchical nature of cgroups. To fix the issue, this patch adds an extra permission requirement when userland tries to migrate a process in the default hierarchy - the issuing task must have write access to the common ancestor of "cgroup.procs" file of the ancestor in addition to the destination's. Conceptually, the issuer must be able to move the target process from the source cgroup to the common ancestor of source and destination cgroups and then to the destination. As long as delegation is done in a proper top-down way, this guarantees that a delegatee can't smuggle processes across disjoint delegation domains. The next patch will add documentation on the delegation model on the default hierarchy. v2: Fixed missing !ret test. Spotted by Li Zefan. Signed-off-by: Tejun Heo Acked-by: Johannes Weiner Cc: Li Zefan

cgroup: separate out cgroup_procs_write_permission() from __cgroup_procs_write()

2015-06-18T20:54:28+00:00

Separate out task / process migration permission check from __cgroup_procs_write() into cgroup_procs_write_permission(). * Permission check is moved right above the actual migration and no longer performed while holding rcu_read_lock(). cgroup_procs_write_permission() uses get_task_cred() / put_cred() instead of __task_cred(). Also, !root trying to migrate kthreadd or PF_NO_SETAFFINITY tasks will now fail with -EINVAL rather than -EACCES which should be fine. * The same permission check is now performed even when moving self by specifying 0 as pid. This always succeeds so there's no functional difference. We'll add more permission checks later and the benefits of keeping both cases consistent outweigh the minute overhead of doing perm checks on pid 0 case. Signed-off-by: Tejun Heo

cgroup: fix uninitialised iterator in for_each_subsys_which

2015-06-10T04:48:30+00:00

Fix the fact that @ssid is uninitialised in the case where CGROUP_SUBSYS_COUNT = 0 by setting ssid to 0. Fixes: cb4a31675270 ("cgroup: use bitmask to filter for_each_subsys") Signed-off-by: Aleksa Sarai Signed-off-by: Tejun Heo

cgroup: replace explicit ss_mask checking with for_each_subsys_which

2015-06-08T09:17:32+00:00

Replace the explicit checking against ss_masks inside a for_each_subsys block with for_each_subsys_which(..., ss_mask), to take advantage of the more readable (and more efficient) macro. Signed-off-by: Aleksa Sarai

cgroup: use bitmask to filter for_each_subsys

2015-06-08T09:17:32+00:00

Add a new macro for_each_subsys_which that allows all enabled cgroup subsystems to be filtered by a bitmask, such that mask & (1 << ssid) determines if the subsystem is to be processed in the loop body (where ssid is the unique id of the subsystem). Also replace the need_forkexit_callback with two separate bitmasks for each callback to make (ss->{fork,exit}) checks unnecessary. tj: add a short comment for "if (!CGROUP_SUBSYS_COUNT)". Signed-off-by: Aleksa Sarai

cgroup: simplify threadgroup locking

2015-05-27T00:35:00+00:00

Now that threadgroup locking is made global, code paths around it can be simplified. * lock-verify-unlock-retry dancing removed from __cgroup_procs_write(). * Race protection against de_thread() removed from cgroup_update_dfl_csses(). Signed-off-by: Tejun Heo

sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem

2015-05-27T00:35:00+00:00

The cgroup side of threadgroup locking uses signal_struct->group_rwsem to synchronize against threadgroup changes. This per-process rwsem adds small overhead to thread creation, exit and exec paths, forces cgroup code paths to do lock-verify-unlock-retry dance in a couple places and makes it impossible to atomically perform operations across multiple processes. This patch replaces signal_struct->group_rwsem with a global percpu_rwsem cgroup_threadgroup_rwsem which is cheaper on the reader side and contained in cgroups proper. This patch converts one-to-one. This does make writer side heavier and lower the granularity; however, cgroup process migration is a fairly cold path, we do want to optimize thread operations over it and cgroup migration operations don't take enough time for the lower granularity to matter. Signed-off-by: Tejun Heo Cc: Ingo Molnar Cc: Peter Zijlstra

sched, cgroup: reorganize threadgroup locking

2015-05-27T00:35:00+00:00

threadgroup_change_begin/end() are used to mark the beginning and end of threadgroup modifying operations to allow code paths which require a threadgroup to stay stable across blocking operations to synchronize against those sections using threadgroup_lock/unlock(). It's currently implemented as a general mechanism in sched.h using per-signal_struct rwsem; however, this never grew non-cgroup use cases and becomes noop if !CONFIG_CGROUPS. It turns out that cgroups is gonna be better served with a different sycnrhonization scheme and is a bit silly to keep cgroups specific details as a general mechanism. What's general here is identifying the places where threadgroups are modified. This patch restructures threadgroup locking so that threadgroup_change_begin/end() become a place where subsystems which need to sycnhronize against threadgroup changes can hook into. cgroup_threadgroup_change_begin/end() which operate on the per-signal_struct rwsem are created and threadgroup_lock/unlock() are moved to cgroup.c and made static. This is pure reorganization which doesn't cause any functional changes. Signed-off-by: Tejun Heo Cc: Ingo Molnar Cc: Peter Zijlstra