Re: [PATCH v2] netprio_cgroup: Fix unlimited memory leak of v2 cgroups

[Tejun Heo]

On Sat, May 09, 2020 at 11:32:10AM +0800, Zefan Li wrote:
> If systemd is configured to use hybrid mode which enables the use of
> both cgroup v1 and v2, systemd will create new cgroup on both the default
> root (v2) and netprio_cgroup hierarchy (v1) for a new session and attach
> task to the two cgroups. If the task does some network thing then the v2
> cgroup can never be freed after the session exited.
> 
> One of our machines ran into OOM due to this memory leak.
> 
> In the scenario described above when sk_alloc() is called cgroup_sk_alloc()
> thought it's in v2 mode, so it stores the cgroup pointer in sk->sk_cgrp_data
> and increments the cgroup refcnt, but then sock_update_netprioidx() thought
> it's in v1 mode, so it stores netprioidx value in sk->sk_cgrp_data, so the
> cgroup refcnt will never be freed.
> 
> Currently we do the mode switch when someone writes to the ifpriomap cgroup
> control file. The easiest fix is to also do the switch when a task is attached
> to a new cgroup.
> 
> Fixes: bd1060a1d671("sock, cgroup: add sock->sk_cgroup")
> Reported-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> Tested-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>

Acked-by: Tejun Heo <tj@xxxxxxxxxx>

Thanks.

-- 
tejun