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

[Jakub Kicinski <kuba@kernel.org>]

On Sat, 9 May 2020 11:32:10 +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")

                     ^ space missing here

> Reported-by: Yang Yingliang <yangyingliang@huawei.com>
> Tested-by: Yang Yingliang <yangyingliang@huawei.com>
> Signed-off-by: Zefan Li <lizefan@huawei.com>
> ---
> 
> forgot to rebase to the latest kernel.
> 
> ---
>  net/core/netprio_cgroup.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> index 8881dd9..9bd4cab 100644
> --- a/net/core/netprio_cgroup.c
> +++ b/net/core/netprio_cgroup.c
> @@ -236,6 +236,8 @@ static void net_prio_attach(struct cgroup_taskset *tset)
>  	struct task_struct *p;
>  	struct cgroup_subsys_state *css;
>  
> +	cgroup_sk_alloc_disable();
> +
>  	cgroup_taskset_for_each(p, css, tset) {
>  		void *v = (void *)(unsigned long)css->id;
>