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

geneve_changelink() applies the new configuration against geneve->net:
geneve_link_config() and the geneve_quiesce()/geneve_unquiesce() pair
reopen the underlay sockets in that netns (geneve_sock_add() uses
geneve->net), so the same reasoning as the tunnel changelink series
applies here.

Gate geneve_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: 2d07dc79fe04 ("geneve: add initial netdev driver for GENEVE tunnels")
Cc: stable@vger.kernel.org
Assisted-by: 0sec:multi-model
Signed-off-by: Doruk Tan Ozturk <redacted>
---
 drivers/net/geneve.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 396e1a113cd4..03c99a016298 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c

@@ -2376,6 +2376,9 @@ static int geneve_changelink(struct net_device *dev, struct nlattr *tb[],
 	struct geneve_config cfg;
 	int err;
 
+	if (!rtnl_dev_link_net_capable(dev, geneve->net))
+		return -EPERM;
+
 	/* If the geneve device is configured for metadata (or externally
 	 * controlled, for example, OVS), then nothing can be changed.
 	 */

-- 
2.43.0