On Fri, Jul 28, 2023 at 5:02 PM Martin KaFai Lau martin.lau@linux.dev 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. 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