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

[Zhang Changzhong]

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@xxxxxxxxxx>
---
 net/sched/cls_u32.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 34d25f7..90ad80b 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -1250,6 +1250,9 @@ static void u32_bind_class(void *fh, u32 classid, unsigned long cl, void *q,
 {
 	struct tc_u_knode *n = fh;
 
+	if (TC_U32_KEY(n->handle) == 0)
+		return;
+
 	tc_cls_bind_class(classid, cl, q, &n->res, base);
 }
 
-- 
2.9.5