cfg80211: check rdev resume callback only for registered wiphy

We got the following use-after-free KASAN report:

 BUG: KASAN: use-after-free in wiphy_resume+0x591/0x5a0 [cfg80211]
	 at addr ffff8803fc244090
 Read of size 8 by task kworker/u16:24/2587
 CPU: 6 PID: 2587 Comm: kworker/u16:24 Tainted: G    B 4.9.13-debug+
 Hardware name: Dell Inc. XPS 15 9550/0N7TVV, BIOS 1.2.19 12/22/2016
 Workqueue: events_unbound async_run_entry_fn
  ffff880425d4f9d8 ffffffffaeedb541 ffff88042b80ef00 ffff8803fc244088
  ffff880425d4fa00 ffffffffae84d7a1 ffff880425d4fa98 ffff8803fc244080
  ffff88042b80ef00 ffff880425d4fa88 ffffffffae84da3a ffffffffc141f7d9
 Call Trace:
  [<ffffffffaeedb541>] dump_stack+0x85/0xc4
  [<ffffffffae84d7a1>] kasan_object_err+0x21/0x70
  [<ffffffffae84da3a>] kasan_report_error+0x1fa/0x500
  [<ffffffffc141f7d9>] ? cfg80211_bss_age+0x39/0xc0 [cfg80211]
  [<ffffffffc141f83a>] ? cfg80211_bss_age+0x9a/0xc0 [cfg80211]
  [<ffffffffae48d46d>] ? trace_hardirqs_on+0xd/0x10
  [<ffffffffc13fb1c0>] ? wiphy_suspend+0xc70/0xc70 [cfg80211]
  [<ffffffffae84def1>] __asan_report_load8_noabort+0x61/0x70
  [<ffffffffc13fb100>] ? wiphy_suspend+0xbb0/0xc70 [cfg80211]
  [<ffffffffc13fb751>] ? wiphy_resume+0x591/0x5a0 [cfg80211]
  [<ffffffffc13fb751>] wiphy_resume+0x591/0x5a0 [cfg80211]
  [<ffffffffc13fb1c0>] ? wiphy_suspend+0xc70/0xc70 [cfg80211]
  [<ffffffffaf3b206e>] dpm_run_callback+0x6e/0x4f0
  [<ffffffffaf3b31b2>] device_resume+0x1c2/0x670
  [<ffffffffaf3b367d>] async_resume+0x1d/0x50
  [<ffffffffae3ee84e>] async_run_entry_fn+0xfe/0x610
  [<ffffffffae3d0666>] process_one_work+0x716/0x1a50
  [<ffffffffae3d05c9>] ? process_one_work+0x679/0x1a50
  [<ffffffffafdd7b6d>] ? _raw_spin_unlock_irq+0x3d/0x60
  [<ffffffffae3cff50>] ? pwq_dec_nr_in_flight+0x2b0/0x2b0
  [<ffffffffae3d1a80>] worker_thread+0xe0/0x1460
  [<ffffffffae3d19a0>] ? process_one_work+0x1a50/0x1a50
  [<ffffffffae3e54c2>] kthread+0x222/0x2e0
  [<ffffffffae3e52a0>] ? kthread_park+0x80/0x80
  [<ffffffffae3e52a0>] ? kthread_park+0x80/0x80
  [<ffffffffae3e52a0>] ? kthread_park+0x80/0x80
  [<ffffffffafdd86aa>] ret_from_fork+0x2a/0x40
 Object at ffff8803fc244088, in cache kmalloc-1024 size: 1024
 Allocated:
 PID = 71
  save_stack_trace+0x1b/0x20
  save_stack+0x46/0xd0
  kasan_kmalloc+0xad/0xe0
  kasan_slab_alloc+0x12/0x20
  __kmalloc_track_caller+0x134/0x360
  kmemdup+0x20/0x50
  brcmf_cfg80211_attach+0x10b/0x3a90 [brcmfmac]
  brcmf_bus_start+0x19a/0x9a0 [brcmfmac]
  brcmf_pcie_setup+0x1f1a/0x3680 [brcmfmac]
  brcmf_fw_request_nvram_done+0x44c/0x11b0 [brcmfmac]
  request_firmware_work_func+0x135/0x280
  process_one_work+0x716/0x1a50
  worker_thread+0xe0/0x1460
  kthread+0x222/0x2e0
  ret_from_fork+0x2a/0x40
 Freed:
 PID = 2568
  save_stack_trace+0x1b/0x20
  save_stack+0x46/0xd0
  kasan_slab_free+0x71/0xb0
  kfree+0xe8/0x2e0
  brcmf_cfg80211_detach+0x62/0xf0 [brcmfmac]
  brcmf_detach+0x14a/0x2b0 [brcmfmac]
  brcmf_pcie_remove+0x140/0x5d0 [brcmfmac]
  brcmf_pcie_pm_leave_D3+0x198/0x2e0 [brcmfmac]
  pci_pm_resume+0x186/0x220
  dpm_run_callback+0x6e/0x4f0
  device_resume+0x1c2/0x670
  async_resume+0x1d/0x50
  async_run_entry_fn+0xfe/0x610
  process_one_work+0x716/0x1a50
  worker_thread+0xe0/0x1460
  kthread+0x222/0x2e0
  ret_from_fork+0x2a/0x40
 Memory state around the buggy address:
  ffff8803fc243f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff8803fc244000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 >ffff8803fc244080: fc fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                          ^
  ffff8803fc244100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8803fc244180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

What is happening is that brcmf_pcie_resume() detects a device that
is no longer responsive and it decides to unbind resulting in a
wiphy_unregister() and wiphy_free() call. Now the wiphy instance
remains allocated, because PM needs to call wiphy_resume() for it.
However, brcmfmac already does a kfree() for the struct
cfg80211_registered_device::ops field. Change the checks in
wiphy_resume() to only access the struct cfg80211_registered_device::ops
if the wiphy instance is still registered at this time.

Cc: stable@vger.kernel.org # 4.10.x, 4.9.x
Reported-by: Daniel J Blueman <daniel@quora.org>
Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/sysfs.c

@@ -132,12 +132,10 @@ static int wiphy_resume(struct device *dev)
 	/* Age scan results with time spent in suspend */
 	cfg80211_bss_age(rdev, get_seconds() - rdev->suspend_at);
 
-	if (rdev->ops->resume) {
-		rtnl_lock();
-		if (rdev->wiphy.registered)
-			ret = rdev_resume(rdev);
-		rtnl_unlock();
-	}
+	rtnl_lock();
+	if (rdev->wiphy.registered && rdev->ops->resume)
+		ret = rdev_resume(rdev);
+	rtnl_unlock();
 
 	return ret;
 }