Re: [PATCH net-next 3/4] bpf: devmap: implement devmap prog execution for generic XDP

This lifts the restriction on running devmap BPF progs in generic
redirect mode. To match native XDP behavior, it is invoked right before
generic_xdp_tx is called, and only supports XDP_PASS/XDP_ABORTED/
XDP_DROP actions.

We also return 0 even if devmap program drops the packet, as
semantically redirect has already succeeded and the devmap prog is the
last point before TX of the packet to device where it can deliver a
verdict on the packet.

This also means it must take care of freeing the skb, as
xdp_do_generic_redirect callers only do that in case an error is
returned.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/devmap.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 2a75e6c2d27d..db3ed8b20c8c 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c

@@ -322,7 +322,8 @@ bool dev_map_can_have_prog(struct bpf_map *map)
 {
 	if ((map->map_type == BPF_MAP_TYPE_DEVMAP ||
 	     map->map_type == BPF_MAP_TYPE_DEVMAP_HASH) &&
-	    map->value_size != offsetofend(struct bpf_devmap_val, ifindex))
+	    map->value_size != offsetofend(struct bpf_devmap_val, ifindex) &&
+	    map->value_size != offsetofend(struct bpf_devmap_val, bpf_prog.fd))
 		return true;