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

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Date:   Fri, 17 Jan 2020 18:12:28 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH v2 2/3] clone3: allow spawning processes into cgroups

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