CVE-2026-63829

In the Linux kernel, the following vulnerability has been resolved:

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

A tunnel 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.

Add rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in

net/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is

skipped when the link netns is dev_net(dev), where the rtnl path already

checked it. The other patches in this series use the same helper.

Gate ipgre_changelink() and erspan_changelink() with it, at the top of

the op before any attribute is parsed, because the parsers update live

tunnel fields first. ipgre_netlink_parms() sets t->collect_md before

ip_tunnel_changelink() runs.

Commit 8b484efd5cb4 ("ip6: vti: Use ip6_tnl.net in

vti6_siocdevprivate().") added the same check on the ioctl path. This

adds it on RTM_NEWLINK.