From: Jamal Hadi Salim <jhs@xxxxxxxxxxxx> commit 02799571714dc5dd6948824b9d080b44a295f695 upstream. Follows up on: https://lore.kernel.org/all/20220809170518.164662-1-cascardo@xxxxxxxxxxxxx/ 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@xxxxxxxxxxxx> Acked-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sched/cls_route.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/net/sched/cls_route.c +++ b/net/sched/cls_route.c @@ -431,6 +431,9 @@ 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) { @@ -483,6 +486,9 @@ static int route4_change(struct net *net int err; bool new = true; + if (!handle) + return -EINVAL; + if (opt == NULL) return handle ? -EINVAL : 0;
