net: implement a SO_DOMAIN getsockoption

This sockopt goes in line with SO_TYPE and SO_PROTOCOL. It makes it
possible for userspace programs to pass around file descriptors — I
am referring to arguments-to-functions, but it may even work for the
fd passing over UNIX sockets — without needing to also pass the
auxiliary information (PF_INET6/IPPROTO_TCP).

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index ebce661234ac..3ac34ea6ec05 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -483,6 +483,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
                 break;
         case SO_TYPE:
         case SO_PROTOCOL:
+        case SO_DOMAIN:
         case SO_ERROR:
                 ret = -ENOPROTOOPT;
                 break;
@@ -769,6 +770,10 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
                 v.val = sk->sk_protocol;
                 break;
 
+        case SO_DOMAIN:
+                v.val = sk->sk_family;
+                break;
+
         case SO_ERROR:
                 v.val = -sock_error(sk);
                 if (v.val == 0)