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

Jun Nie
2022-12-14T02:21:14Z

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@syzkaller.appspotmail.com
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Signed-off-by: Jun Nie <jun.nie@linaro.org>
---
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