On Wed, May 20, 2020 at 10:24 AM Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> ---
>
> Discovered while working on bpf_link support for netns-attached progs.
> Looks like bpf tree material so pushing it out separately.
>
> -jkbs
>
[...]
> /**
> * __skb_flow_get_ports - extract the upper layer ports and return them
> * @skb: sk_buff to extract the ports from
> @@ -1827,6 +1848,8 @@ EXPORT_SYMBOL(flow_keys_basic_dissector);
>
> static int __init init_default_flow_dissectors(void)
> {
> + int err;
> +
> skb_flow_dissector_init(&flow_keys_dissector,
> flow_keys_dissector_keys,
> ARRAY_SIZE(flow_keys_dissector_keys));
> @@ -1836,7 +1859,11 @@ static int __init init_default_flow_dissectors(void)
> skb_flow_dissector_init(&flow_keys_basic_dissector,
> flow_keys_basic_dissector_keys,
> ARRAY_SIZE(flow_keys_basic_dissector_keys));
> - return 0;
> +
> + err = register_pernet_subsys(&flow_dissector_pernet_ops);
> +
> + WARN_ON(err);
syzbot simulates memory allocation failures, which can bubble up here,
so this WARN_ON will probably trigger. I wonder if this could be
rewritten so that init fails, when registration fails? What are the
consequences?
> + return err;
> }
>
> core_initcall(init_default_flow_dissectors);
> --
> 2.25.4
>
