netdev - [PATCH net,v2 3/3] net: sched: sfb: fix null pointer access issue when sfb

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Date:   Tue, 18 Oct 2022 14:32:01 +0800
From:   Zhengchao Shao <shaozhengchao@...wei.com>
To:     <cake@...ts.bufferbloat.net>, <netdev@...r.kernel.org>,
        <toke@...e.dk>, <jhs@...atatu.com>, <xiyou.wangcong@...il.com>,
        <jiri@...nulli.us>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>
CC:     <dave.taht@...il.com>, <weiyongjun1@...wei.com>,
        <yuehaibing@...wei.com>, <shaozhengchao@...wei.com>
Subject: [PATCH net,v2 3/3] net: sched: sfb: fix null pointer access issue when sfb_init() fails

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@...wei.com>
---
 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);
 	q->slot = 0;
 	q->double_buffering = false;
 	sfb_zero_all_buckets(q);
-- 
2.17.1