On 06/23/2019 04:17 AM, Toke Høiland-Jørgensen wrote:
> From: Toke Høiland-Jørgensen <[email protected]>
>
> The bpf_redirect_map() helper used by XDP programs doesn't return any
> indication of whether it can successfully redirect to the map index it was
> given. Instead, BPF programs have to track this themselves, leading to
> programs using duplicate maps to track which entries are populated in the
> devmap.
>
> This patch fixes this by moving the map lookup into the bpf_redirect_map()
> helper, which makes it possible to return failure to the eBPF program. The
> lower bits of the flags argument is used as the return code, which means
> that existing users who pass a '0' flag argument will get XDP_ABORTED.
>
> With this, a BPF program can check the return code from the helper call and
> react by, for instance, substituting a different redirect. This works for
> any type of map used for redirect.
>
> Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 183bf4d8e301..a6779e1cc1b8 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3605,17 +3605,13 @@ static int xdp_do_redirect_map(struct net_device
> *dev, struct xdp_buff *xdp,
> struct bpf_redirect_info *ri)
> {
> u32 index = ri->ifindex;
> - void *fwd = NULL;
> + void *fwd = ri->item;
> int err;
>
> ri->ifindex = 0;
> + ri->item = NULL;
> WRITE_ONCE(ri->map, NULL);
>
> - fwd = __xdp_map_lookup_elem(map, index);
> - if (unlikely(!fwd)) {
> - err = -EINVAL;
> - goto err;
> - }
If you look at the _trace_xdp_redirect{,_err}(), we should also get rid of the
extra NULL test in devmap_ifindex() which is not under tracepoint static key.
