[PATCH bpf-next v2 1/2] bpf: allow to retrieve sol_socket opts from sock_addr progs

[Daniel Borkmann]

The _bpf_setsockopt() is able to set some of the SOL_SOCKET level options,
however, _bpf_getsockopt() has little support to actually retrieve them.
This small patch adds few misc options such as SO_MARK, SO_PRIORITY and
SO_BINDTOIFINDEX. For the latter getter and setter are added. The mark and
priority in particular allow to retrieve the options from BPF cgroup hooks
to then implement custom behavior / settings on the syscall hooks compared
to other sockets that stick to the defaults, for example.

Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Acked-by: Yonghong Song <y...@fb.com>
---
 net/core/filter.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 255aeee72402..9ab94e90d660 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4770,6 +4770,10 @@ static int _bpf_setsockopt(struct sock *sk, int level, 
int optname,
                                ifindex = dev->ifindex;
                                dev_put(dev);
                        }
+                       fallthrough;
+               case SO_BINDTOIFINDEX:
+                       if (optname == SO_BINDTOIFINDEX)
+                               ifindex = val;
                        ret = sock_bindtoindex(sk, ifindex, false);
                        break;
                case SO_KEEPALIVE:
@@ -4932,8 +4936,25 @@ static int _bpf_getsockopt(struct sock *sk, int level, 
int optname,
 
        sock_owned_by_me(sk);
 
+       if (level == SOL_SOCKET) {
+               if (optlen != sizeof(int))
+                       goto err_clear;
+
+               switch (optname) {
+               case SO_MARK:
+                       *((int *)optval) = sk->sk_mark;
+                       break;
+               case SO_PRIORITY:
+                       *((int *)optval) = sk->sk_priority;
+                       break;
+               case SO_BINDTOIFINDEX:
+                       *((int *)optval) = sk->sk_bound_dev_if;
+                       break;
+               default:
+                       goto err_clear;
+               }
 #ifdef CONFIG_INET
-       if (level == SOL_TCP && sk->sk_prot->getsockopt == tcp_getsockopt) {
+       } else if (level == SOL_TCP && sk->sk_prot->getsockopt == 
tcp_getsockopt) {
                struct inet_connection_sock *icsk;
                struct tcp_sock *tp;
 
@@ -4986,12 +5007,12 @@ static int _bpf_getsockopt(struct sock *sk, int level, 
int optname,
                default:
                        goto err_clear;
                }
+#endif
 #endif
        } else {
                goto err_clear;
        }
        return 0;
-#endif
 err_clear:
        memset(optval, 0, optlen);
        return -EINVAL;
-- 
2.21.0