[PATCH 5.15 761/779] net_sched: cls_route: remove from list when handle is 0

[Greg Kroah-Hartman]

From: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>

commit 9ad36309e2719a884f946678e0296be10f0bb4c1 upstream.

When a route filter is replaced and the old filter has a 0 handle, the old
one won't be removed from the hashtable, while it will still be freed.

The test was there since before commit 1109c00547fc ("net: sched: RCU
cls_route"), when a new filter was not allocated when there was an old one.
The old filter was reused and the reinserting would only be necessary if an
old filter was replaced. That was still wrong for the same case where the
old handle was 0.

Remove the old filter from the list independently from its handle value.

This fixes CVE-2022-2588, also reported as ZDI-CAN-17440.

Reported-by: Zhenpeng Lin <zplin@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Reviewed-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220809170518.164662-1-cascardo@xxxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/sched/cls_route.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/sched/cls_route.c
+++ b/net/sched/cls_route.c
@@ -526,7 +526,7 @@ static int route4_change(struct net *net
 	rcu_assign_pointer(f->next, f1);
 	rcu_assign_pointer(*fp, f);
 
-	if (fold && fold->handle && f->handle != fold->handle) {
+	if (fold) {
 		th = to_hash(fold->handle);
 		h = from_hash(fold->handle >> 16);
 		b = rtnl_dereference(head->table[th]);