From 2a3fc78210b9f0e85372a2435368962009f480fc Mon Sep 17 00:00:00 2001
From: Zhengchao Shao <shaozhengchao@huawei.com>
Date: Tue, 18 Oct 2022 14:32:01 +0800
Subject: [PATCH] net: sched: sfb: fix null pointer access issue when
 sfb_init() fails
Git-commit: 2a3fc78210b9f0e85372a2435368962009f480fc
Patch-mainline: v6.1-rc2
References: bsc#1207361

When the default qdisc is sfb, if the qdisc of dev_queue fails to be
inited during mqprio_init(), sfb_reset() is invoked to clear resources.
In this case, the q->qdisc is NULL, and it will cause gpf issue.

The process is as follows:
qdisc_create_dflt()
	sfb_init()
		tcf_block_get()          --->failed, q->qdisc is NULL
	...
	qdisc_put()
		...
		sfb_reset()
			qdisc_reset(q->qdisc)    --->q->qdisc is NULL
				ops = qdisc->ops

The following is the Call Trace information:
general protection fault, probably for non-canonical address
0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
RIP: 0010:qdisc_reset+0x2b/0x6f0
Call Trace:
<TASK>
sfb_reset+0x37/0xd0
qdisc_reset+0xed/0x6f0
qdisc_destroy+0x82/0x4c0
qdisc_put+0x9e/0xb0
qdisc_create_dflt+0x2c3/0x4a0
mqprio_init+0xa71/0x1760
qdisc_create+0x3eb/0x1000
tc_modify_qdisc+0x408/0x1720
rtnetlink_rcv_msg+0x38e/0xac0
netlink_rcv_skb+0x12d/0x3a0
netlink_unicast+0x4a2/0x740
netlink_sendmsg+0x826/0xcc0
sock_sendmsg+0xc5/0x100
____sys_sendmsg+0x583/0x690
___sys_sendmsg+0xe8/0x160
__sys_sendmsg+0xbf/0x160
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7f2164122d04
</TASK>

Fixes: e13e02a3c68d ("net_sched: SFB flow scheduler")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Wiesner <jwiesner@suse.de>
---
 net/sched/sch_sfb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_sfb.c b/net/sched/sch_sfb.c
index e2389fa3cff8..73ae2e726512 100644
--- a/net/sched/sch_sfb.c
+++ b/net/sched/sch_sfb.c
@@ -455,7 +455,8 @@ static void sfb_reset(struct Qdisc *sch)
 {
 	struct sfb_sched_data *q = qdisc_priv(sch);
 
-	qdisc_reset(q->qdisc);
+	if (likely(q->qdisc))
+		qdisc_reset(q->qdisc);
 	sch->qstats.backlog = 0;
 	sch->q.qlen = 0;
 	q->slot = 0;
-- 
2.35.3