Re: [PATCH 4.19 016/133] cgroup: fix cgroup_sk_alloc() for sk_clone_lock()

[Yang Yingliang]

On 2020/8/13 19:41, Greg Kroah-Hartman wrote:
> On Thu, Aug 13, 2020 at 07:30:55PM +0800, Yang Yingliang wrote:
> > Hi,
> >
> > On 2020/7/20 23:36, Greg Kroah-Hartman wrote:
> > > From: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> > >
> > > [ Upstream commit ad0f75e5f57ccbceec13274e1e242f2b5a6397ed ]
> > >
> > > 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.
> > >
> > > The global variable 'cgroup_sk_alloc_disabled' is used to determine
> > > whether to take these reference counts. It is impossible to make
> > > the reference counting correct unless we save this bit of information
> > > in skcd->val. So, add a new bit there to record whether the socket
> > > has already taken the reference counts. This obviously relies on
> > > kmalloc() to align cgroup pointers to at least 4 bytes,
> > > ARCH_KMALLOC_MINALIGN is certainly larger than that.
> > >
> > > This bug seems to be introduced since the beginning, commit
> > > d979a39d7242 ("cgroup: duplicate cgroup reference when cloning sockets")
> > > tried to fix it but not compeletely. It seems not easy to trigger until
> > > the recent commit 090e28b229af
> > > ("netprio_cgroup: Fix unlimited memory leak of v2 cgroups") was merged.
> > >
> > > Fixes: bd1060a1d671 ("sock, cgroup: add sock->sk_cgroup")
> > > Reported-by: Cameron Berkenpas <cam@xxxxxxxxxxx>
> > > Reported-by: Peter Geis <pgwipeout@xxxxxxxxx>
> > > Reported-by: Lu Fengqi <lufq.fnst@xxxxxxxxxxxxxx>
> > > Reported-by: Daniël Sonck <dsonck92@xxxxxxxxx>
> > > Reported-by: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>
> > > Tested-by: Cameron Berkenpas <cam@xxxxxxxxxxx>
> > > Tested-by: Peter Geis <pgwipeout@xxxxxxxxx>
> > > Tested-by: Thomas Lamprecht <t.lamprecht@xxxxxxxxxxx>
> > > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > > Cc: Zefan Li <lizefan@xxxxxxxxxx>
> > > Cc: Tejun Heo <tj@xxxxxxxxxx>
> > > Cc: Roman Gushchin <guro@xxxxxx>
> > > Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> > > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > ---
> > [...]
> > > +void cgroup_sk_clone(struct sock_cgroup_data *skcd)
> > > +{
> > > +	/* Socket clone path */
> > > +	if (skcd->val) {
> > Compare to mainline patch, it's missing *if (skcd->no_refcnt)* check here.
> >
> > Is it a mistake here ?
> Possibly, it is in the cgroup_sk_free() call.  Can you send a patch to
> fix this up?

OK, I checked other stable branches, it also need be fixed in stable-4.9 
and stable-4.14.

I will send the patches to these branches.

> thanks,
>
> greg k-h
> .