On Thu, May 21, 2020 at 12:09 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> 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?
good catch. that warn is pointless.
I removed it and force pushed the bpf tree.
