net: sched: sfb: fix null pointer access issue when sfb_init() fails

In the Linux kernel, the following vulnerability has been resolved:

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>