Re: [PATCH v2 2/3] clone3: allow spawning processes into cgroups

From: Christian Brauner <christian.brauner@ubuntu.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Li Zefan <lizefan@huawei.com>,
	Peter Zijlstra <peterz@infradead.org>,
	cgroups@vger.kernel.org
Subject: Re: [PATCH v2 2/3] clone3: allow spawning processes into cgroups
Date: Fri, 17 Jan 2020 18:12:28 +0100	[thread overview]
Message-ID: <20200117171228.evtvrny3v7zjcocd@wittgenstein> (raw)
In-Reply-To: <20200117165311.GH2677547@devbig004.ftw2.facebook.com>

On Fri, Jan 17, 2020 at 08:53:11AM -0800, Tejun Heo wrote:
> Hello, Christian.
> 
> Sorry about late reply.
> 
> On Thu, Jan 16, 2020 at 01:29:44PM +0100, Christian Brauner wrote:
> > Could it be that you misread cgroup_attach_permissions()? Because it
> > does check for write permissions on the destination cgroup.procs file.
> > That's why I've added the cgroup_get_from_file() helper. :) See:
> > 
> > static int cgroup_attach_permissions(struct cgroup *src_cgrp,
> > 				     struct cgroup *dst_cgrp,
> > 				     struct super_block *sb, bool thread)
> > {
> > 	int ret = 0;
> > 
> > 	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, sb);
> > 	if (ret)
> > 		return ret;
> 
> So, if you look at cgroup_procs_write_permission(), it's only checking
> the write perm of the common ancestor, not the destination because it
> assumes that the destination is already checked by the vfs layer, and
> we need to check both.

Ok, gimme 20 min.

Thanks!
Christian