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

vti_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 vti_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: 895de9a3488a ("vti4: Enable namespace changing")
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/20260612085941.3158249-4-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 95b6bb78fcd274ec38ebda549e91d9cc0b38e3f9..3b80929994a007f1faf85d5e658f3fb61de290de 100644 (file)
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -596,6 +596,9 @@ static int vti_changelink(struct net_device *dev, struct nlattr *tb[],
        struct ip_tunnel_parm_kern p;
        __u32 fwmark = t->fwmark;
 
+       if (!rtnl_dev_link_net_capable(dev, t->net))
+               return -EPERM;
+
        vti_netlink_parms(data, &p, &fwmark);
        return ip_tunnel_changelink(dev, tb, &p, fwmark);
 }