[IPV6]: Fix IPV6_UNICAST_HOPS getsockopt().

> Relevant standard (RFC 3493) notes:
>
>    The IPV6_UNICAST_HOPS option may be used with getsockopt() to
>    determine the hop limit value that the system will use for subsequent
>    unicast packets sent via that socket.
>
> I don't reckon -1 could be the hop limit value.

-1 means un-initialized.

> IMHO, the value from
> case 1 (if socket is connected to some destination), otherwise case 2
> (if bound to a scope interface) or ultimately the default hop limit
> ought to be returned instead, as it will be most often correct, while
> the current behavior is always wrong, unless setsockopt() has been used
> first. I don't if some people may think doing a route lookup in
> getsockopt might be overly expensive, but at least the two other cases
> should be ok, particularly the last one.

The following patch seems to work for me, but this code has behaved this
way for a while, so don't know if it will break any existing apps.

Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 19 insertions, 4 deletions

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 1eafcfc95e81..352690e2ab82 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -978,12 +978,27 @@ static int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
                 break;
 
         case IPV6_UNICAST_HOPS:
-                val = np->hop_limit;
-                break;
-
         case IPV6_MULTICAST_HOPS:
-                val = np->mcast_hops;
+        {
+                struct dst_entry *dst;
+
+                if (optname == IPV6_UNICAST_HOPS)
+                        val = np->hop_limit;
+                else
+                        val = np->mcast_hops;
+
+                dst = sk_dst_get(sk);
+                if (dst) {
+                        if (val < 0)
+                                val = dst_metric(dst, RTAX_HOPLIMIT);
+                        if (val < 0)
+                                val = ipv6_get_hoplimit(dst->dev);
+                        dst_release(dst);
+                }
+                if (val < 0)
+                        val = ipv6_devconf.hop_limit;
                 break;
+        }
 
         case IPV6_MULTICAST_LOOP:
                 val = np->mc_loop;