[PATCH net v6 5/7] net: ip6_gre: require CAP_NET_ADMIN in the device netns for changelink

[Maoyi Xie <maoyixie.tju@gmail.com>]

ip6gre_changelink() and ip6erspan_changelink() operate on at most two
netns, dev_net(dev) and the tunnel link netns t->net. They differ once
the device is created in or moved to a netns other than the one the
request runs in. The rtnl changelink path checks CAP_NET_ADMIN only
against dev_net(dev), so a caller privileged there but not in t->net can
rewrite a tunnel that lives in t->net.

Gate both ops on rtnl_dev_link_net_capable() at their top, before any
attribute is parsed.

Reported-by: Xiao Liang <shaw.leon@gmail.com>
Closes: https://lore.kernel.org/netdev/CABAhCOSzP1vaThGV35_VnsRCb=87_CPjPVsTHbq905k8A+BuUg@mail.gmail.com/
Fixes: 690afc165bb3 ("net: ip6_gre: fix moving ip6gre between namespaces")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/ipv6/ip6_gre.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 365b4059eb20..8ebc99a299c9 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -2047,6 +2047,9 @@ static int ip6gre_changelink(struct net_device *dev, struct nlattr *tb[],
 	struct ip6gre_net *ign = net_generic(t->net, ip6gre_net_id);
 	struct __ip6_tnl_parm p;
 
+	if (!rtnl_dev_link_net_capable(dev, t->net))
+		return -EPERM;
+
 	t = ip6gre_changelink_common(dev, tb, data, &p, extack);
 	if (IS_ERR(t))
 		return PTR_ERR(t);
@@ -2266,6 +2269,9 @@ static int ip6erspan_changelink(struct net_device *dev, struct nlattr *tb[],
 	struct __ip6_tnl_parm p;
 	struct ip6gre_net *ign;
 
+	if (!rtnl_dev_link_net_capable(dev, t->net))
+		return -EPERM;
+
 	ign = net_generic(t->net, ip6gre_net_id);
 	t = ip6gre_changelink_common(dev, tb, data, &p, extack);
 	if (IS_ERR(t))
-- 
2.34.1