bpf_xdp_redirect_map: Perform map lookup in eBPF helper

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 <toke@redhat.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 92bd192f7786..1fe53e78c7e3 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -580,6 +580,7 @@ struct bpf_skb_data_end {
 struct bpf_redirect_info {
 	u32 flags;
 	u32 tgt_index;
+	void *tgt_value;
 	struct bpf_map *map;
 	struct bpf_map *map_to_flush;
 	u32 kern_flags;