On 7/31/23 2:35 PM, Yan Zhai wrote:
On Fri, Jul 28, 2023 at 5:02 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
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;
Just fixing skb redirect return code won't be sufficient. I realized
there are other return paths that need to be treated, e.g. bpf reroute
path also directly returns dev_queue_xmit status. I plan to check for
LWTUNNEL_XMIT_CONTINUE (and change it to a value that does not
conflict with NET_RX_DROP and NET_XMIT_DROP) in the next revision. On
the other hand, the return value of NETDEV_TX_BUSY is another hassle.
I suspect we are talking about different things or I am still missing something.
I was thinking skb_do_redirect() should have always consumed the skb and
bpf_xmit should always return LWTUNNEL_XMIT_DONE also (instead of
LWTUNNEL_XMIT_CONTINUE described in the this patch commit message). It is what
sch_handle_egress() is doing also. Could you explain how is it different from
the skb_do_redirect usage in sch_handle_egress() or you are suggesting the
current sch_handle_egress() has the issue too also?
As Dan suggested, packets might not have been freed when this is
returned from drivers. The caller of dev_queue_xmit might need to free
skb when this happens.
Yan
