Re: [PATCH 2/2] xdp: adjust xdp redirect tracepoint to include return error code
flat view
From: John Fastabend <john.fastabend@gmail.com>
Date: 2017-08-17 18:46:19
On 08/17/2017 09:22 AM, Jesper Dangaard Brouer wrote:
The return error code need to be included in the tracepoint xdp:xdp_redirect, else its not possible to distinguish successful or failed XDP_REDIRECT transmits. XDP have no queuing mechanism. Thus, it is fairly easily to overrun a NIC transmit queue. The eBPF program invoking helpers (bpf_redirect or bpf_redirect_map) to redirect a packet doesn't get any feedback whether the packet was actually transmitted. Info on failed transmits in the tracepoint xdp:xdp_redirect, is interesting as this opens for providing a feedback-loop to the receiving XDP program. Signed-off-by: Jesper Dangaard Brouer <redacted> ---
[...]
quoted hunk ↗ jump to hunk
@@ -2532,12 +2535,14 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp, ri->map = NULL; if (unlikely(!fwd)) { bpf_warn_invalid_xdp_redirect(index); - return -EINVAL; + err = -EINVAL; + goto out;
It doesn't look like there is a check in trace_xdp_redirect to avoid dereferencing a NULL fwd pointer here (*to in trace code path). Did I miss something?
quoted hunk ↗ jump to hunk
} - trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT); - - return __bpf_tx_xdp(fwd, NULL, xdp, 0); + err = __bpf_tx_xdp(fwd, NULL, xdp, 0); +out: + trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT, err); + return err; } EXPORT_SYMBOL_GPL(xdp_do_redirect);