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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Roman Gushchin <guro@fb.com>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	linux-kernel@vger.kernel.org, kernel-team@fb.com,
	netdev@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH bpf] bpf: cgroup: prevent out-of-order release of cgroup bpf
Date: Fri, 3 Jan 2020 16:35:25 -0800
Message-ID: <20200104003523.rfte5rw6hbnncjes@ast-mbp> (raw)
In-Reply-To: <20191227215034.3169624-1-guro@fb.com>

On Fri, Dec 27, 2019 at 01:50:34PM -0800, Roman Gushchin wrote:
> Before commit 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf
> from cgroup itself") cgroup bpf structures were released with
> corresponding cgroup structures. It guaranteed the hierarchical order
> of destruction: children were always first. It preserved attached
> programs from being released before their propagated copies.
> 
> But with cgroup auto-detachment there are no such guarantees anymore:
> cgroup bpf is released as soon as the cgroup is offline and there are
> no live associated sockets. It means that an attached program can be
> detached and released, while its propagated copy is still living
> in the cgroup subtree. This will obviously lead to an use-after-free
> bug.
...
> @@ -65,6 +65,9 @@ static void cgroup_bpf_release(struct work_struct *work)
>  
>  	mutex_unlock(&cgroup_mutex);
>  
> +	for (p = cgroup_parent(cgrp); p; p = cgroup_parent(p))
> +		cgroup_bpf_put(p);
> +

The fix makes sense, but is it really safe to walk cgroup hierarchy
without holding cgroup_mutex?


  parent reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-27 21:50 Roman Gushchin
2020-01-03 15:30 ` Roman Gushchin
2020-01-03 17:47 ` Song Liu
2020-01-04  0:35 ` Alexei Starovoitov [this message]
2020-01-04  1:13   ` Roman Gushchin
2020-01-04  2:31     ` Alexei Starovoitov
2020-01-04  3:00       ` Roman Gushchin
2020-01-06 22:07         ` Alexei Starovoitov
2020-01-06 22:20           ` Roman Gushchin

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