sched, bpf: add helper for retrieving routing realms

Using routing realms as part of the classifier is quite useful, it
can be viewed as a tag for one or multiple routing entries (think of
an analogy to net_cls cgroup for processes), set by user space routing
daemons or via iproute2 as an indicator for traffic classifiers and
later on processed in the eBPF program.

Unlike actions, the classifier can inspect device flags and enable
netif_keep_dst() if necessary. tc actions don't have that possibility,
but in case people know what they are doing, it can be used from there
as well (e.g. via devs that must keep dsts by design anyway).

If a realm is set, the handler returns the non-zero realm. User space
can set the full 32bit realm for the dst.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 7eeffaf69c75..5faaa5425f7b 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -262,7 +262,8 @@ static int cls_bpf_prog_from_ops(struct nlattr **tb, struct cls_bpf_prog *prog)
         return 0;
 }
 
-static int cls_bpf_prog_from_efd(struct nlattr **tb, struct cls_bpf_prog *prog)
+static int cls_bpf_prog_from_efd(struct nlattr **tb, struct cls_bpf_prog *prog,
+                                 const struct tcf_proto *tp)
 {
         struct bpf_prog *fp;
         char *name = NULL;
@@ -294,6 +295,9 @@ static int cls_bpf_prog_from_efd(struct nlattr **tb, struct cls_bpf_prog *prog)
         prog->bpf_name = name;
         prog->filter = fp;
 
+        if (fp->dst_needed)
+                netif_keep_dst(qdisc_dev(tp->q));
+
         return 0;
 }
 
@@ -330,7 +334,7 @@ static int cls_bpf_modify_existing(struct net *net, struct tcf_proto *tp,
         prog->exts_integrated = have_exts;
 
         ret = is_bpf ? cls_bpf_prog_from_ops(tb, prog) :
-                       cls_bpf_prog_from_efd(tb, prog);
+                       cls_bpf_prog_from_efd(tb, prog, tp);
         if (ret < 0) {
                 tcf_exts_destroy(&exts);
                 return ret;