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authorEric W. Biederman <ebiederm@xmission.com>2016-07-15 06:35:24 -0500
committerTejun Heo <tj@kernel.org>2016-07-15 07:56:32 -0400
commit7bd8830875bfa380c68f390efbad893293749324 (patch)
tree86f51feccb725f56d42fd3cca7e256a787cfec13 /kernel/cgroup.c
parent82d6489d0fed2ec8a8c48c19e8d8a04ac8e5bb26 (diff)
downloadlinux-7bd8830875bfa380c68f390efbad893293749324.tar.bz2
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>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c5
1 files changed, 1 insertions, 4 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75c0ff00aca6..5f01e00cffc4 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6309,14 +6309,11 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
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)) {