[PATCH 6.1 262/609] vxlan: require CAP_NET_ADMIN in the device netns for changelink

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Doruk Tan Ozturk <[email protected]>

commit 3a61bd9637f3d929aa846e4eb3d98b48c26fcb0e upstream.

A tunnel changelink() operates on at most two netns, dev_net(dev) and
the sticky underlay netns vxlan->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 vxlan->net can rewrite a vxlan
device whose underlay lives in vxlan->net.

vxlan_changelink() validates and applies the new configuration against
vxlan->net (vxlan_config_validate(vxlan->net, ...)) and can reopen the
underlay socket in that netns, so the same reasoning as the tunnel
changelink series applies here.

Gate vxlan_changelink() with rtnl_dev_link_net_capable(), at the top of
the op before any attribute is parsed, matching ipgre_changelink() and
the rest of the "require CAP_NET_ADMIN in the device netns for
changelink" series.

Found by 0sec automated security-research tooling (https://0sec.ai).

Fixes: 8bcdc4f3a20b ("vxlan: add changelink support")
Cc: [email protected]
Signed-off-by: Doruk Tan Ozturk <[email protected]>
Reviewed-by: Fernando Fernandez Mancera <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/vxlan/vxlan_core.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -4249,6 +4249,9 @@ static int vxlan_changelink(struct net_d
 	struct vxlan_rdst *dst;
 	int err;
 
+	if (!rtnl_dev_link_net_capable(dev, vxlan->net))
+		return -EPERM;
+
 	dst = &vxlan->default_dst;
 	err = vxlan_nl2conf(tb, data, dev, &conf, true, extack);
 	if (err)