[PATCH v2] net: inet_diag: always export IPV6_V6ONLY sockopt for listening sockets

[Phil Sutter <phil@nwl.cc>]

Reconsidering my commit 20462155 "net: inet_diag: export IPV6_V6ONLY
sockopt", I am not happy with the limitations it causes for socket
analysing code in userspace. Exporting the value only if it is set makes
it hard for userspace to decide whether the option is not set or the
kernel does not support exporting the option at all.

>From an auditor's perspective, the interesting question for listening
AF_INET6 sockets is: "Does it NOT have IPV6_V6ONLY set?" Because it is
the unexpected case. This patch allows to answer this question reliably.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Cc: Eric Dumazet <edumazet@google.com>
---
Changes since v1:
- Export the value only for listening sockets, as suggested by Eric Dumazet.
- Adjusted commit message accordingly.
---
 net/ipv4/inet_diag.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 9bc2667..c3b1f3a 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -152,8 +152,8 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 				       inet6_sk(sk)->tclass) < 0)
 				goto errout;
 
-		if (ipv6_only_sock(sk) &&
-		    nla_put_u8(skb, INET_DIAG_SKV6ONLY, 1))
+		if (((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE)) &&
+		    nla_put_u8(skb, INET_DIAG_SKV6ONLY, ipv6_only_sock(sk)))
 			goto errout;
 	}
 #endif
-- 
2.1.2