[PATCH net] netdev-genl: avoid empty messages in queue dump

[Jakub Kicinski <kuba@kernel.org>]

Empty netlink responses from do() are not correct (as opposed to
dump() where not dumping anything is perfectly fine).
We should return an error if the target object does not exist,
in this case if the netdev is down it has no queues.

Fixes: 6b6171db7fc8 ("netdev-genl: Add netlink framework functions for queue")
Reported-by: syzbot+0a884bc2d304ce4af70f@syzkaller.appspotmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: jdamato@fastly.com
CC: almasrymina@google.com
CC: sridhar.samudrala@intel.com
CC: amritha.nambiar@intel.com
---
 net/core/netdev-genl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 9527dd46e4dc..b4becd4065d9 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -430,10 +430,10 @@ static int
 netdev_nl_queue_fill(struct sk_buff *rsp, struct net_device *netdev, u32 q_idx,
 		     u32 q_type, const struct genl_info *info)
 {
-	int err = 0;
+	int err;
 
 	if (!(netdev->flags & IFF_UP))
-		return err;
+		return -ENOENT;
 
 	err = netdev_nl_queue_validate(netdev, q_idx, q_type);
 	if (err)
-- 
2.47.1