4.7-stable review patch. If anyone has any objections, please let me know.
------------------ From: Eric W. Biederman <[email protected]> commit 7bd8830875bfa380c68f390efbad893293749324 upstream. If "clone(CLONE_NEWCGROUP...)" is called it results in a nice lockdep valid splat. In __cgroup_proc_write the lock ordering is: cgroup_mutex -- through cgroup_kn_lock_live cgroup_threadgroup_rwsem In copy_process the guts of clone the lock ordering is: cgroup_threadgroup_rwsem -- through threadgroup_change_begin cgroup_mutex -- through copy_namespaces -- copy_cgroup_ns lockdep reports some a different call chains for the first ordering of cgroup_mutex and cgroup_threadgroup_rwsem but it is harder to trace. This is most definitely deadlock potential under the right circumstances. Fix this by by skipping the cgroup_mutex and making the locking in copy_cgroup_ns mirror the locking in cgroup_post_fork which also runs during fork under the cgroup_threadgroup_rwsem. Fixes: a79a908fd2b0 ("cgroup: introduce cgroup namespaces") Signed-off-by: "Eric W. Biederman" <[email protected]> Signed-off-by: Tejun Heo <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/cgroup.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -6309,14 +6309,11 @@ struct cgroup_namespace *copy_cgroup_ns( if (!ns_capable(user_ns, CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); - mutex_lock(&cgroup_mutex); + /* It is not safe to take cgroup_mutex here */ spin_lock_irq(&css_set_lock); - cset = task_css_set(current); get_css_set(cset); - spin_unlock_irq(&css_set_lock); - mutex_unlock(&cgroup_mutex); new_ns = alloc_cgroup_ns(); if (IS_ERR(new_ns)) {
