[PATCH bpf-next] bpf/xdp: Can't detach BPF XDP prog if not exist

[Zhengchao Shao]

if user sets nonexistent xdp_flags to detach xdp prog, kernel should
return err and tell user that detach failed with detail info.

Signed-off-by: Zhengchao Shao <shaozhengchao@xxxxxxxxxx>
---
 net/core/dev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 8ed0272bf32f..8ed05ef62c68 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9149,6 +9149,12 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
 		return -EBUSY;
 	}
 
+	/* no BPF XDP prog attached */
+	if (!new_prog && !(dev->xdp_state[mode].prog)) {
+		NL_SET_ERR_MSG(extack, "no BPF XDP prog attached");
+		return -ENOENT;
+	}
+
 	/* don't allow if an upper device already has a program */
 	netdev_for_each_upper_dev_rcu(dev, upper, iter) {
 		if (dev_xdp_prog_count(upper) > 0) {
-- 
2.17.1