net: ipip: require CAP_NET_ADMIN in the device netns for changelink

ipip_changelink() operates 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 ipip_changelink() on rtnl_dev_link_net_capable() at its 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: 6c742e714d8c ("ipip: add x-netns support")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260612085941.3158249-3-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index 4f89a03e0b49b8fb328077a68fb72d7e4f5768ca..b643194f57d29f74981f50b81c83df47462d9f81 100644 (file)
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -494,6 +494,9 @@ static int ipip_changelink(struct net_device *dev, struct nlattr *tb[],
        bool collect_md;
        __u32 fwmark = t->fwmark;
 
+       if (!rtnl_dev_link_net_capable(dev, t->net))
+               return -EPERM;
+
        if (ip_tunnel_netlink_encap_parms(data, &ipencap)) {
                int err = ip_tunnel_encap_setup(t, &ipencap);