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Date: Thu, 18 Jun 2020 12:36:11 -0700 From: Roman Gushchin <guro@...com> To: Cong Wang <xiyou.wangcong@...il.com> CC: Zefan Li <lizefan@...wei.com>, Linux Kernel Network Developers <netdev@...r.kernel.org>, Cameron Berkenpas <cam@...-zeon.de>, Peter Geis <pgwipeout@...il.com>, Lu Fengqi <lufq.fnst@...fujitsu.com>, Daniƫl Sonck <dsonck92@...il.com>, Daniel Borkmann <daniel@...earbox.net>, Tejun Heo <tj@...nel.org> Subject: Re: [Patch net] cgroup: fix cgroup_sk_alloc() for sk_clone_lock() On Thu, Jun 18, 2020 at 12:19:13PM -0700, Cong Wang wrote: > On Wed, Jun 17, 2020 at 6:44 PM Zefan Li <lizefan@...wei.com> wrote: > > > > Cc: Roman Gushchin <guro@...com> > > > > Thanks for fixing this. > > > > On 2020/6/17 2:03, Cong Wang wrote: > > > When we clone a socket in sk_clone_lock(), its sk_cgrp_data is > > > copied, so the cgroup refcnt must be taken too. And, unlike the > > > sk_alloc() path, sock_update_netprioidx() is not called here. > > > Therefore, it is safe and necessary to grab the cgroup refcnt > > > even when cgroup_sk_alloc is disabled. > > > > > > sk_clone_lock() is in BH context anyway, the in_interrupt() > > > would terminate this function if called there. And for sk_alloc() > > > skcd->val is always zero. So it's safe to factor out the code > > > to make it more readable. > > > > > > Fixes: 090e28b229af92dc5b ("netprio_cgroup: Fix unlimited memory leak of v2 cgroups") > > > > but I don't think the bug was introduced by this commit, because there > > are already calls to cgroup_sk_alloc_disable() in write_priomap() and > > write_classid(), which can be triggered by writing to ifpriomap or > > classid in cgroupfs. This commit just made it much easier to happen > > with systemd invovled. > > > > I think it's 4bfc0bb2c60e2f4c ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself"), > > which added cgroup_bpf_get() in cgroup_sk_alloc(). > > Good point. > > I take a deeper look, it looks like commit d979a39d7242e06 > is the one to blame, because it is the first commit that began to > hold cgroup refcnt in cgroup_sk_alloc(). I agree, ut seems that the issue is not related to bpf and probably can be reproduced without CONFIG_CGROUP_BPF. d979a39d7242e06 indeed seems closer to the origin. Btw, based on the number of reported-by tags it seems that there was a real issue which the patch is fixing. Maybe you'll a couple of words about how it reveals itself in the real life? Thanks!
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