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

[Song Liu]

On Fri, Dec 27, 2019 at 1:50 PM Roman Gushchin <guro@xxxxxx> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Roman Gushchin <guro@xxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

LGTM. Thanks for the fix!

Acked-by: Song Liu <songliubraving@xxxxxx>