netdev - net-next: KSZ switch driver oops in ksz_mib_read

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Date:   Tue, 11 Jun 2019 11:57:13 -0600
From:   Robert Hancock <hancock@...systems.ca>
To:     netdev@...r.kernel.org
Cc:     woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com
Subject: net-next: KSZ switch driver oops in ksz_mib_read_work

We are using an embedded platform with a KSZ9897 switch. I am getting
the oops below in ksz_mib_read_work when testing with net-next branch.
After adding in some debug output, the problem is in this code:

	for (i = 0; i < dev->mib_port_cnt; i++) {
		p = &dev->ports[i];
		mib = &p->mib;
		mutex_lock(&mib->cnt_mutex);

		/* Only read MIB counters when the port is told to do.
		 * If not, read only dropped counters when link is not up.
		 */
		if (!p->read) {
			const struct dsa_port *dp = dsa_to_port(dev->ds, i);

			if (!netif_carrier_ok(dp->slave))
				mib->cnt_ptr = dev->reg_mib_cnt;
		}

The oops is happening on port index 3 (i.e. 4th port) which is not
connected on our platform and so has no entry in the device tree. For
that port, dp->slave is NULL and so netif_carrier_ok explodes.

If I change the code to skip the port entirely in the loop if dp->slave
is NULL it seems to fix the crash, but I'm not that familiar with this
code. Can someone confirm whether that is the proper fix?

[   17.842829] Unable to handle kernel NULL pointer dereference at
virtual address 0000002c
[   17.850983] pgd = (ptrval)
[   17.853711] [0000002c] *pgd=00000000
[   17.857317] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
[   17.862632] Modules linked in:
[   17.865695] CPU: 1 PID: 21 Comm: kworker/1:1 Not tainted 5.2.0-rc3 #1
[   17.872142] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[   17.878688] Workqueue: events ksz_mib_read_work
[   17.883227] PC is at ksz_mib_read_work+0x58/0x94
[   17.887848] LR is at ksz_mib_read_work+0x38/0x94
[   17.887852] pc : [<c04843dc>]    lr : [<c04843bc>]    psr: 60070113
[   17.887857] sp : e8147f08  ip : e8148000  fp : ffffe000
[   17.887860] r10: 00000000  r9 : e8aa7040  r8 : e867cc44
[   17.887865] r7 : 00000c20  r6 : e8aa7120  r5 : 00000003  r4 : e867c958
[   17.887868] r3 : 00000000  r2 : 00000000  r1 : 00000003  r0 : e8aa7040
[   17.887879] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM
Segment none
[   17.948224] Control: 10c5387d  Table: 38d9404a  DAC: 00000051
[   17.948230] Process kworker/1:1 (pid: 21, stack limit = 0x(ptrval))
[   17.948236] Stack: (0xe8147f08 to 0xe8148000)
[   17.948245] 7f00:                   e8aa7120 e80a8080 eb7aef40
eb7b2000 00000000 e8aa7124
[   17.948254] 7f20: 00000000 c013865c 00000008 c0b03d00 e80a8080
e80a8094 eb7aef40 00000008
[   17.958073] systemd[1]: storage.mount: Unit is bound to inactive unit
dev-mmcblk1p2.device. Stopping, too.
[   17.963306] 7f40: c0b03d00 eb7aef58 eb7aef40 c01393a0 ffffe000
c0b46b09 c084e464 00000000
[   17.963314] 7f60: ffffe000 e8053140 e80530c0 00000000 e8146000
e80a8080 c013935c e80a1eac
[   17.963322] 7f80: e805315c c013e78c 00000000 e80530c0 c013e648
00000000 00000000 00000000
[   17.969893] random: systemd: uninitialized urandom read (16 bytes read)
[   17.973942] 7fa0: 00000000 00000000 00000000 c01010e8 00000000
00000000 00000000 00000000
[   17.973949] 7fc0: 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000
[   17.973958] 7fe0: 00000000 00000000 00000000 00000000 00000013
00000000 00000000 00000000
[   17.982246] random: systemd: uninitialized urandom read (16 bytes read)
[   17.990329] [<c04843dc>] (ksz_mib_read_work) from [<c013865c>]
(process_one_work+0x17c/0x390)
[   17.990345] [<c013865c>] (process_one_work) from [<c01393a0>]
(worker_thread+0x44/0x518)
[   18.009394] random: systemd: uninitialized urandom read (16 bytes read)
[   18.016344] [<c01393a0>] (worker_thread) from [<c013e78c>]
(kthread+0x144/0x14c)
[   18.016358] [<c013e78c>] (kthread) from [<c01010e8>]
(ret_from_fork+0x14/0x2c)
[   18.016362] Exception stack(0xe8147fb0 to 0xe8147ff8)
[   18.016369] 7fa0:                                     00000000
00000000 00000000 00000000
[   18.031159] 7fc0: 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000
[   18.031166] 7fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[   18.031176] Code: 1a000006 e51630e0 e0833405 e5933050 (e593302c)
[   18.031279] ---[ end trace ca82392a6c2aa959 ]---


-- 
Robert Hancock
Senior Software Developer
SED Systems, a division of Calian Ltd.
Email: hancock@...systems.ca