From: Jamal Hadi Salim <jhs@mojatatu.com>
Date: Sun, 14 Aug 2022 11:27:58 +0000
Subject: net_sched: cls_route: disallow handle of 0
Patch-mainline: v6.0-rc2
Git-commit: 02799571714dc5dd6948824b9d080b44a295f695
References: bsc#1202393

Follows up on:
https://lore.kernel.org/all/20220809170518.164662-1-cascardo@canonical.com/

handle of 0 implies from/to of universe realm which is not very
sensible.

Lets see what this patch will do:
$sudo tc qdisc add dev $DEV root handle 1:0 prio

//lets manufacture a way to insert handle of 0
$sudo tc filter add dev $DEV parent 1:0 protocol ip prio 100 \
route to 0 from 0 classid 1:10 action ok

//gets rejected...
Error: handle of 0 is not valid.
We have an error talking to the kernel, -1

//lets create a legit entry..
sudo tc filter add dev $DEV parent 1:0 protocol ip prio 100 route from 10 \
classid 1:10 action ok

//what did the kernel insert?
$sudo tc filter ls dev $DEV parent 1:0
filter protocol ip pref 100 route chain 0
filter protocol ip pref 100 route chain 0 fh 0x000a8000 flowid 1:10 from 10
	action order 1: gact action pass
	 random type none pass val 0
	 index 1 ref 1 bind 1

//Lets try to replace that legit entry with a handle of 0
$ sudo tc filter replace dev $DEV parent 1:0 protocol ip prio 100 \
handle 0x000a8000 route to 0 from 0 classid 1:10 action drop

Error: Replacing with handle of 0 is invalid.
We have an error talking to the kernel, -1

And last, lets run Cascardo's POC:
$ ./poc
0
0
-22
-22
-22

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

SLE15-LTSS / SLE12-SP4-LTSS: as extack is not passed to route4_set_parms()
and route4_change(), omit setting the error message and just bail out.

---
 net/sched/cls_route.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/net/sched/cls_route.c
+++ b/net/sched/cls_route.c
@@ -427,6 +427,9 @@ static int route4_set_parms(struct net *
 			return -EINVAL;
 	}
 
+	if (!nhandle)
+		return -EINVAL;
+
 	h1 = to_hash(nhandle);
 	b = rtnl_dereference(head->table[h1]);
 	if (!b) {
@@ -472,6 +475,9 @@ static int route4_change(struct net *net, struct sk_buff *in_skb,
 	int err;
 	bool new = true;
 
+	if (!handle)
+		return -EINVAL;
+
 	if (opt == NULL)
 		return handle ? -EINVAL : 0;