Messages in this thread | | | Date | Fri, 28 Jul 2023 15:02:19 -0700 | Subject | Re: [PATCH v4 bpf 1/2] bpf: fix skb_do_redirect return values | From | Martin KaFai Lau <> |
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On 7/25/23 6:08 PM, Yan Zhai wrote: > skb_do_redirect returns various of values: error code (negative), > 0 (success), and some positive status code, e.g. NET_XMIT_CN, > NET_RX_DROP. Commit 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel > infrastructure") didn't check the return code correctly, so positive > values are propagated back along call chain: > > ip_finish_output2 > -> bpf_xmit > -> run_lwt_bpf > -> skb_do_redirect
From looking at skb_do_redirect, the skb_do_redirect should have consumed the skb except for the -EAGAIN return value. afaik, -EAGAIN could only happen by using the bpf_redirect_peer helper. lwt does not have the bpf_redirect_peer helper available, so there is no -EAGAIN case in lwt. iow, skb_do_redirect should have always consumed the skb in lwt. or did I miss something?
If that is the case, it feels like the fix should be in run_lwt_bpf() and the "if (ret == 0)" test in run_lwt_bpf() is unnecessary?
ret = skb_do_redirect(skb); if (ret == 0) ret = BPF_REDIRECT;
> > Inside ip_finish_output2, redirected skb will continue to neighbor > subsystem as if LWTUNNEL_XMIT_CONTINUE is returned, despite that this > skb could have been freed. The bug can trigger use-after-free warning > and crashes kernel afterwards: > > https://gist.github.com/zhaiyan920/8fbac245b261fe316a7ef04c9b1eba48
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