netdev - Re: [PATCH bpf v2] flow_dissector: Drop BPF flow dissector prog ref on netns cleanup

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Date:   Thu, 21 May 2020 08:21:11 -0700
From:   sdf@...gle.com
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        kernel-team@...udflare.com,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH bpf v2] flow_dissector: Drop BPF flow dissector prog ref
 on netns cleanup

On 05/21, Jakub Sitnicki wrote:
> When attaching a flow dissector program to a network namespace with
> bpf(BPF_PROG_ATTACH, ...) we grab a reference to bpf_prog.

> If netns gets destroyed while a flow dissector is still attached, and  
> there
> are no other references to the prog, we leak the reference and the program
> remains loaded.

> Leak can be reproduced by running flow dissector tests from selftests/bpf:

>    # bpftool prog list
>    # ./test_flow_dissector.sh
>    ...
>    selftests: test_flow_dissector [PASS]
>    # bpftool prog list
>    4: flow_dissector  name _dissect  tag e314084d332a5338  gpl
>            loaded_at 2020-05-20T18:50:53+0200  uid 0
>            xlated 552B  jited 355B  memlock 4096B  map_ids 3,4
>            btf_id 4
>    #

> Fix it by detaching the flow dissector program when netns is going away.

> Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
Reviewed-by: Stanislav Fomichev <sdf@...gle.com>

Thank you!