[PATCH net v2] net: sched: ematch: reject invalid data

[Jun Nie]

syzbot reported below bug. Refuse to compare for invalid data case to fix
it.

general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 6 Comm: kworker/0:0 Not tainted 5.15.77-syzkaller-00764-g7048384c9872 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Workqueue: wg-crypt-wg2 wg_packet_tx_worker
RIP: 0010:em_cmp_match+0x4e/0x5f0 net/sched/em_cmp.c:25
Call Trace:
 <TASK>
 tcf_em_match net/sched/ematch.c:492 [inline]
 __tcf_em_tree_match+0x194/0x720 net/sched/ematch.c:518
 tcf_em_tree_match include/net/pkt_cls.h:463 [inline]
 basic_classify+0xd8/0x250 net/sched/cls_basic.c:48
 __tcf_classify net/sched/cls_api.c:1549 [inline]
 tcf_classify+0x161/0x430 net/sched/cls_api.c:1589
 prio_classify net/sched/sch_prio.c:42 [inline]
 prio_enqueue+0x1d3/0x6a0 net/sched/sch_prio.c:75
 dev_qdisc_enqueue net/core/dev.c:3792 [inline]
 __dev_xmit_skb+0x35c/0x1650 net/core/dev.c:3876
 __dev_queue_xmit+0x8f3/0x1b50 net/core/dev.c:4193
 dev_queue_xmit+0x17/0x20 net/core/dev.c:4261
 neigh_hh_output include/net/neighbour.h:508 [inline]
 neigh_output include/net/neighbour.h:522 [inline]
 ip_finish_output2+0xc0f/0xf00 net/ipv4/ip_output.c:228
 __ip_finish_output+0x163/0x370
 ip_finish_output+0x20b/0x220 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:299 [inline]
 ip_output+0x1e9/0x410 net/ipv4/ip_output.c:430
 dst_output include/net/dst.h:450 [inline]
 ip_local_out+0x92/0xb0 net/ipv4/ip_output.c:126
 iptunnel_xmit+0x4a2/0x890 net/ipv4/ip_tunnel_core.c:82
 udp_tunnel_xmit_skb+0x1b6/0x2c0 net/ipv4/udp_tunnel_core.c:175
 send4+0x78d/0xd20 drivers/net/wireguard/socket.c:85
 wg_socket_send_skb_to_peer+0xd5/0x1d0 drivers/net/wireguard/socket.c:175
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x202/0x560 drivers/net/wireguard/send.c:276
 process_one_work+0x6db/0xc00 kernel/workqueue.c:2313
 worker_thread+0xb3e/0x1340 kernel/workqueue.c:2460
 kthread+0x41c/0x500 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Reported-by: syzbot+963f7637dae8becc038f@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Signed-off-by: Jun Nie <jun.nie@xxxxxxxxxx>
---
 net/sched/em_cmp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/sched/em_cmp.c b/net/sched/em_cmp.c
index f17b049ea530..0284394be53f 100644
--- a/net/sched/em_cmp.c
+++ b/net/sched/em_cmp.c
@@ -22,9 +22,14 @@ static int em_cmp_match(struct sk_buff *skb, struct tcf_ematch *em,
 			struct tcf_pkt_info *info)
 {
 	struct tcf_em_cmp *cmp = (struct tcf_em_cmp *) em->data;
-	unsigned char *ptr = tcf_get_base_ptr(skb, cmp->layer) + cmp->off;
+	unsigned char *ptr;
 	u32 val = 0;
 
+	if (!cmp)
+		return 0;
+
+	ptr = tcf_get_base_ptr(skb, cmp->layer) + cmp->off;
+
 	if (!tcf_valid_offset(skb, ptr, cmp->align))
 		return 0;
 
-- 
2.34.1