[PATCH net] tun: drop batched packets while the device is down

tun_sendmsg() handles TUN_MSG_PTR batches from vhost-net by calling
tun_xdp_one() instead of tun_get_user(). But this path does not check
IFF_UP, allowing packets from a guest to be injected into the host
receive path while the device is administratively down.

Check IFF_UP in tun_xdp_one() before running XDP or building an skb.
Drop the packet when the device is down, matching tun_get_user().

Fixes: 043d222f93ab ("tuntap: accept an array of XDP buffs through sendmsg()")
Signed-off-by: Xiao Liang <redacted>
---
 drivers/net/tun.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 439565a264ee..2cb0de36e186 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2551,6 +2551,12 @@ static int tun_xdp_one(struct tun_struct *tun,
 		return -EINVAL;
 	}
 
+	if (unlikely(!(READ_ONCE(tun->dev->flags) & IFF_UP))) {
+		put_page(virt_to_head_page(xdp->data));
+		dev_core_stats_rx_dropped_inc(tun->dev);
+		return -EIO;
+	}
+
 	xdp_prog = rcu_dereference(tun->xdp_prog);
 	if (xdp_prog) {
 		if (gso->gso_type) {

-- 
2.56.0