linux-kernel - Re: [PATCH bpf] bpf: cgroup: prevent out-of-order release of cgroup bpf

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Date:   Fri, 3 Jan 2020 09:47:01 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     Roman Gushchin <guro@...com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        open list <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: cgroup: prevent out-of-order release of cgroup bpf

On Fri, Dec 27, 2019 at 1:50 PM Roman Gushchin <guro@...com> 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.
>
[...]
>
> Thanks to Josef Bacik for the debugging and the initial analysis of
> the problem.
>
> Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself")
> Reported-by: Josef Bacik <josef@...icpanda.com>
> Signed-off-by: Roman Gushchin <guro@...com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: stable@...r.kernel.org

LGTM. Thanks for the fix!

Acked-by: Song Liu <songliubraving@...com>