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Subject[PATCHv1] ipv6: Fix RTM_GETROUTE's interpretation of RTA_IIF to be consistent with ipv4
In IPv4, if an RTA_IIF attribute is specified within an RTM_GETROUTE
message, then a route is searched as if a packet was received on the
specified 'iif' interface.

However in IPv6, RTA_IIF is not interpreted in the same way:
'inet6_rtm_getroute()' always calls 'ip6_route_output()', regardless the
RTA_IIF attribute.

As a result, in IPv6 there's no way to use RTM_GETROUTE in order to look
for a route as if a packet was received on a specific interface.

Fix 'inet6_rtm_getroute()' so that RTA_IIF is interpreted as "lookup a
route as if a packet was received on the specified interface", similar
to IPv4's 'inet_rtm_getroute()' interpretation.

Reported-by: Ami Koren <amikoren@yahoo.com>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
---

Tested on v3.2.6. Patch applies to v3.3.

Few points to review:

1) An alternative: construction of an skb within 'inet6_rtm_getroute()'
and then calling 'ip6_route_input()' with the skb as an argument.
Thus, no need to split common code of 'ip6_route_input()'.
Less elegant IMO.

2) Better name for the new common function 'ip6_route_input_lookup()'
Will happily accept any better suggestions.

3) In IPv4 the 'ip_route_input()' call within 'inet_rtm_getroute()'is
protected by a 'local_bh_disable()' since dawn of history.
Not sure if similar protection needed within 'inet6_rtm_getroute()'.

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 22b7664..1178345 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -868,6 +868,16 @@ static struct rt6_info *ip6_pol_route_input(struct net *net, struct fib6_table *
return ip6_pol_route(net, table, fl6->flowi6_iif, fl6, flags);
}

+static struct dst_entry *ip6_route_input_lookup(struct net *net,
+ struct net_device *dev,
+ struct flowi6 *fl6, int flags)
+{
+ if (rt6_need_strict(&fl6->daddr) && dev->type != ARPHRD_PIMREG)
+ flags |= RT6_LOOKUP_F_IFACE;
+
+ return fib6_rule_lookup(net, fl6, flags, ip6_pol_route_input);
+}
+
void ip6_route_input(struct sk_buff *skb)
{
const struct ipv6hdr *iph = ipv6_hdr(skb);
@@ -882,10 +892,7 @@ void ip6_route_input(struct sk_buff *skb)
.flowi6_proto = iph->nexthdr,
};

- if (rt6_need_strict(&iph->daddr) && skb->dev->type != ARPHRD_PIMREG)
- flags |= RT6_LOOKUP_F_IFACE;
-
- skb_dst_set(skb, fib6_rule_lookup(net, &fl6, flags, ip6_pol_route_input));
+ skb_dst_set(skb, ip6_route_input_lookup(net, skb->dev, &fl6, flags));
}

static struct rt6_info *ip6_pol_route_output(struct net *net, struct fib6_table *table,
@@ -2520,7 +2527,7 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr* nlh, void
struct sk_buff *skb;
struct rtmsg *rtm;
struct flowi6 fl6;
- int err, iif = 0;
+ int err, iif = 0, oif = 0;

err = nlmsg_parse(nlh, sizeof(*rtm), tb, RTA_MAX, rtm_ipv6_policy);
if (err < 0)
@@ -2547,15 +2554,29 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr* nlh, void
iif = nla_get_u32(tb[RTA_IIF]);

if (tb[RTA_OIF])
- fl6.flowi6_oif = nla_get_u32(tb[RTA_OIF]);
+ oif = nla_get_u32(tb[RTA_OIF]);

if (iif) {
struct net_device *dev;
+ int flags = 0;
+
dev = __dev_get_by_index(net, iif);
if (!dev) {
err = -ENODEV;
goto errout;
}
+
+ fl6.flowi6_iif = iif;
+
+ if (!ipv6_addr_any(&fl6.saddr))
+ flags |= RT6_LOOKUP_F_HAS_SADDR;
+
+ rt = (struct rt6_info *)ip6_route_input_lookup(net, dev, &fl6,
+ flags);
+ } else {
+ fl6.flowi6_oif = oif;
+
+ rt = (struct rt6_info *)ip6_route_output(net, NULL, &fl6);
}

skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
@@ -2570,7 +2591,6 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr* nlh, void
skb_reset_mac_header(skb);
skb_reserve(skb, MAX_HEADER + sizeof(struct ipv6hdr));

- rt = (struct rt6_info*) ip6_route_output(net, NULL, &fl6);
skb_dst_set(skb, &rt->dst);

err = rt6_fill_node(net, skb, rt, &fl6.daddr, &fl6.saddr, iif,

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