cgroupns: Fix the locking in copy_cgroup_ns
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.
Cc: stable@vger.kernel.org
Fixes: a79a908fd2b0 ("cgroup: introduce cgroup namespaces")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75c0ff0..5f01e00 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6309,14 +6309,11 @@
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)) {