BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Jakub Sitnicki <jakub@cloudflare.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	kernel-team <kernel-team@cloudflare.com>,
	Petar Penkov <ppenkov@google.com>,
	Stanislav Fomichev <sdf@google.com>
Subject: Re: [PATCH bpf] flow_dissector: Drop BPF flow dissector prog ref on netns cleanup
Date: Thu, 21 May 2020 17:53:14 -0700
Message-ID: <CAADnVQKztsp-fF5Mbi7DUGrM-5SfH24xntaF0Qaewxr9ax7ZRw@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzbpMp9D0TsC5dhRJ-AeKqsXJ5EyEcCx2-kkZg+ZBnHYqg@mail.gmail.com>

On Thu, May 21, 2020 at 12:09 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Wed, May 20, 2020 at 10:24 AM Jakub Sitnicki <jakub@cloudflare.com> 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@cloudflare.com>
> > ---
> >
> > 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.

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-20 17:22 Jakub Sitnicki
2020-05-20 17:40 ` sdf
2020-05-21  0:56   ` Alexei Starovoitov
2020-05-21  8:42   ` Jakub Sitnicki
2020-05-21 19:08 ` Andrii Nakryiko
2020-05-22  0:53   ` Alexei Starovoitov [this message]
2020-05-22  8:22     ` Jakub Sitnicki

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAADnVQKztsp-fF5Mbi7DUGrM-5SfH24xntaF0Qaewxr9ax7ZRw@mail.gmail.com \
    --to=alexei.starovoitov@gmail.com \
    --cc=andrii.nakryiko@gmail.com \
    --cc=bpf@vger.kernel.org \
    --cc=jakub@cloudflare.com \
    --cc=kernel-team@cloudflare.com \
    --cc=netdev@vger.kernel.org \
    --cc=ppenkov@google.com \
    --cc=sdf@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git