Subject: Re: Fw: [Bugme-new] [Bug 7665] New: getsockopt(IPV6_*CAST_HOPS) returns -1

From: Brian Haley <[email-masked]>
Date: Tue, 12 Dec 2006 16:16:27 -0500

>>> Where fd is a socket (datagram or raw) with IPv6 protocol family,
>>> getsockopt(fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, ...) succeeds, but
>>> the returned hop limit is -1. connect()'ing the socket first does
>>> not solve the problem.
>> An IPv6 socket's hoplimit value is not set at creation time, instead,
>> the hoplimit in an outgoing packet is set dynamically at transmit
>> time to one of the following (in this order):
>>
>> 1. Hoplimit route metric (if set)
>> 2. Outgoing interface value (/proc/sys/net/ipv6/conf/ethX/hop_limit)
>> 3. Global IPv6 value (/proc/sys/net/ipv6/conf/all/hop_limit)
>>
>> A setsockopt() value *will* override this.
> 
> 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.

-Brian

Signed-off-by: Brian Haley <[email-masked]>

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 1eafcfc..352690e 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -978,12 +978,27 @@ static int do_ipv6_getsockopt(struct soc
 		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;