From: Yan Zhai <yan@cloudflare.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: "open list:BPF [NETWORKING] (tc BPF,
sock_addr)" <bpf@vger.kernel.org>,
kernel-team@cloudflare.com,
Martin KaFai Lau <martin.lau@linux.dev>,
Daniel Borkmann <daniel@iogearbox.net>,
John Fastabend <john.fastabend@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
Yonghong Song <yhs@fb.com>, KP Singh <kpsingh@kernel.org>,
Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
"open list:BPF [NETWORKING] (tc BPF,
sock_addr)" <netdev@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
Jordan Griege <jgriege@cloudflare.com>
Subject: Re: [PATCH] bpf: lwt: do not return NET_XMIT_xxx values on bpf_redirect
Date: Tue, 18 Jul 2023 22:21:41 -0500 [thread overview]
Message-ID: <CAO3-PbqF_JMyHK2hE=MH9cF3i2xVQ-vpQhdZ7HG4uVM7jan4xw@mail.gmail.com> (raw)
In-Reply-To: <CAKH8qBsZeqchfcYm-pNKjafYwFzGnwzcXDgHfj3Omkm0yWd31A@mail.gmail.com>
On Tue, Jul 18, 2023 at 3:29 PM Stanislav Fomichev <sdf@google.com> wrote:
>
> On Tue, Jul 18, 2023 at 11:22 AM Yan Zhai <yan@cloudflare.com> wrote:
> >
> > skb_do_redirect handles returns error code from both rx and tx path.
> > The tx path codes are special, e.g. NET_XMIT_CN: they are
> > non-negative, and can conflict with LWTUNNEL_XMIT_xxx values. Directly
> > returning such code can cause unexpected behavior. We found at least
> > one bug that will panic the kernel through KASAN report when we
> > accidentally redirect packets to a down or carrier-down device at lwt
> > xmit hook:
> >
> > https://gist.github.com/zhaiyan920/8fbac245b261fe316a7ef04c9b1eba48
> >
> > Above bug is hit because NET_XMIT_CN is returned by noop_qdisc of the
> > down device, and it propagates from dev_queue_xmit all way to the lwt
> > logic. Although skb has been freed by the qdisc, it still continues to
> > neighbor subsystem and triggers the bug.
> >
> > This change converts the tx code to proper errors that lwt can consume.
> >
> > Reported-by: Jordan Griege <jgriege@cloudflare.com>
> > Signed-off-by: Yan Zhai <yan@cloudflare.com>
> > ---
> > net/core/filter.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 06ba0e56e369..c9cc501ecdc0 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -2129,6 +2129,11 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
> > ret = dev_queue_xmit(skb);
> > dev_xmit_recursion_dec();
> >
> > + // We should not return NET_XMIT_xxx here since it will conflict with
> > + // LWTUNNEL_XMIT_xxx values. Convert the return value to errno instead.
>
> C++ comments; should be /* */. But, also, maybe they are not really needed?
>
*facepalm* yes I think we can remove them since the commit message
already covers it...
> ret = dev_queue_xmit(skb);
> if (ret)
> ret = net_xmit_errno(ret);
>
> We have a bunch of places with the pattern like this, so probably can
> do the same here?
>
Personally I like an explicit name better, since not all the return
codes use 0 to signal success, e.g. XDP_PASS, TC_ACT_PIPE. But I'd
leave that for future improvements now that all other places use 0 on
this.
thanks
Yan
> > + if (unlikely(ret != NET_XMIT_SUCCESS))
> > + ret = net_xmit_errno(ret);
> > +
> > return ret;
> > }
> >
> > --
> > 2.30.2
> >
--
Yan
prev parent reply other threads:[~2023-07-19 3:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-18 18:22 [PATCH] bpf: lwt: do not return NET_XMIT_xxx values on bpf_redirect Yan Zhai
2023-07-18 20:28 ` Stanislav Fomichev
2023-07-19 3:21 ` Yan Zhai [this message]
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