net/sched: cls_u32: skip hash tables in u32_bind_class()

net/sched: cls_u32: skip hash tables in u32_bind_class()

u32_walk() enumerates both struct tc_u_hnode and struct tc_u_knode
through the walker callback. u32_bind_class() unconditionally casts the
passed fh to tc_u_knode and accesses &n->res, so when fh is actually a
tc_u_hnode, which has no tcf_result member, this results in a
slab-out-of-bounds read of res->classid in tc_cls_bind_class().

The issue can be reproduced with the following commands:

    tc qdisc add dev lo root handle 1: hfsc
    tc class add dev lo parent 1: classid 1:1 hfsc sc rate 1000kbit
    tc filter add dev lo parent 1:1 protocol ip prio 1 u32 match u32 0 0 flowid 1:1
    tc class add dev lo parent 1: classid 1:2 hfsc sc rate 2000kbit

Fix this by skipping hash tables via the TC_U32_KEY(handle) check.

Fixes: 07d79fc7d94e ("net_sched: add reverse binding for tc class")
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/1786089038-36366-1-git-send-email-zhangchangzhong@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>