drm/i915: Fix use after free in lpe_audio_platdev_destroy()

[31908.547136] BUG: KASAN: use-after-free in intel_lpe_audio_teardown+0x78/0xb0 [i915] at addr ffff8801f7788358
[31908.547297] Read of size 8 by task drv_selftest/3781
[31908.547405] CPU: 0 PID: 3781 Comm: drv_selftest Tainted: G    BU  W       4.10.0+ #451
[31908.547553] Hardware name:                  /        , BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015
[31908.547682] Call Trace:
[31908.547772]  dump_stack+0x68/0x9f
[31908.547857]  kasan_object_err+0x1c/0x70
[31908.547947]  kasan_report_error+0x1f1/0x4f0
[31908.548038]  ? kfree+0xaa/0x170
[31908.548121]  kasan_report+0x34/0x40
[31908.548211]  ? klist_children_get+0x20/0x30
[31908.548472]  ? intel_lpe_audio_teardown+0x78/0xb0 [i915]
[31908.548567]  __asan_load8+0x5e/0x70
[31908.548824]  intel_lpe_audio_teardown+0x78/0xb0 [i915]
[31908.549080]  intel_audio_deinit+0x28/0x80 [i915]
[31908.549315]  i915_driver_unload+0xe4/0x360 [i915]
[31908.549551]  ? i915_driver_load+0x1d70/0x1d70 [i915]
[31908.549651]  ? trace_hardirqs_on+0xd/0x10
[31908.549885]  i915_pci_remove+0x23/0x30 [i915]
[31908.549978]  pci_device_remove+0x5c/0x100
[31908.550069]  device_release_driver_internal+0x1db/0x2e0
[31908.550165]  driver_detach+0x68/0xc0
[31908.550256]  bus_remove_driver+0x8b/0x150
[31908.550346]  driver_unregister+0x3e/0x60
[31908.550439]  pci_unregister_driver+0x1d/0x110
[31908.550531]  ? find_module_all+0x7a/0xa0
[31908.550791]  i915_exit+0x1a/0x87 [i915]
[31908.550881]  SyS_delete_module+0x264/0x2c0
[31908.550971]  ? free_module+0x430/0x430
[31908.551064]  ? trace_hardirqs_off_caller+0x16/0x110
[31908.551159]  ? trace_hardirqs_on_caller+0x16/0x280
[31908.551256]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[31908.551350]  entry_SYSCALL_64_fastpath+0x1c/0xb1
[31908.551440] RIP: 0033:0x7f1d67312ec7
[31908.551520] RSP: 002b:00007ffebe34e888 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
[31908.551650] RAX: ffffffffffffffda RBX: ffffffff811123f6 RCX: 00007f1d67312ec7
[31908.551743] RDX: 0000000000000000 RSI: 0000000000000800 RDI: 0000560d0af476b8
[31908.551837] RBP: ffff880233d87f98 R08: 0000000000000000 R09: 00007ffebe34e8b8
[31908.551930] R10: 00007f1d68adf8c0 R11: 0000000000000206 R12: 0000000000000000
[31908.552023] R13: 0000560d0af46440 R14: 0000000000000034 R15: 00007ffebe34d860
[31908.552121]  ? trace_hardirqs_off_caller+0x16/0x110
[31908.552217] Object at ffff8801f7788000, in cache kmalloc-2048 size: 2048
[31908.552306] Allocated:
[31908.552377] PID = 3781
[31908.552456]  save_stack_trace+0x16/0x20
[31908.552539]  kasan_kmalloc+0xee/0x190
[31908.552627]  __kmalloc+0xdb/0x1b0
[31908.552713]  platform_device_alloc+0x27/0x90
[31908.552804]  platform_device_register_full+0x36/0x220
[31908.553066]  intel_lpe_audio_init+0x41e/0x570 [i915]
[31908.553320]  intel_audio_init+0xd/0x40 [i915]
[31908.553552]  i915_driver_load+0x13f5/0x1d70 [i915]
[31908.553788]  i915_pci_probe+0x65/0xe0 [i915]
[31908.553881]  pci_device_probe+0xda/0x140
[31908.553969]  driver_probe_device+0x400/0x660
[31908.554058]  __driver_attach+0x11c/0x120
[31908.554147]  bus_for_each_dev+0xe6/0x150
[31908.554237]  driver_attach+0x26/0x30
[31908.554325]  bus_add_driver+0x26b/0x3b0
[31908.554412]  driver_register+0xce/0x190
[31908.554502]  __pci_register_driver+0xaf/0xc0
[31908.554589]  0xffffffffa0550063
[31908.554675]  do_one_initcall+0x8b/0x1e0
[31908.554764]  do_init_module+0x102/0x325
[31908.554852]  load_module+0x3aad/0x45e0
[31908.554944]  SyS_finit_module+0x169/0x1a0
[31908.555033]  entry_SYSCALL_64_fastpath+0x1c/0xb1
[31908.555119] Freed:
[31908.555188] PID = 3781
[31908.555266]  save_stack_trace+0x16/0x20
[31908.555349]  kasan_slab_free+0xb0/0x180
[31908.555436]  kfree+0xaa/0x170
[31908.555520]  platform_device_release+0x76/0x80
[31908.555610]  device_release+0x45/0xe0
[31908.555698]  kobject_put+0x11f/0x260
[31908.555785]  put_device+0x12/0x20
[31908.555871]  platform_device_unregister+0x1b/0x20
[31908.556135]  intel_lpe_audio_teardown+0x5c/0xb0 [i915]
[31908.556390]  intel_audio_deinit+0x28/0x80 [i915]
[31908.556622]  i915_driver_unload+0xe4/0x360 [i915]
[31908.556858]  i915_pci_remove+0x23/0x30 [i915]
[31908.556948]  pci_device_remove+0x5c/0x100
[31908.557037]  device_release_driver_internal+0x1db/0x2e0
[31908.557129]  driver_detach+0x68/0xc0
[31908.557217]  bus_remove_driver+0x8b/0x150
[31908.557304]  driver_unregister+0x3e/0x60
[31908.557394]  pci_unregister_driver+0x1d/0x110
[31908.557653]  i915_exit+0x1a/0x87 [i915]
[31908.557741]  SyS_delete_module+0x264/0x2c0
[31908.557834]  entry_SYSCALL_64_fastpath+0x1c/0xb1
[31908.557919] Memory state around the buggy address:
[31908.558005]  ffff8801f7788200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[31908.558127]  ffff8801f7788280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[31908.558255] >ffff8801f7788300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[31908.558374]                                                     ^
[31908.558467]  ffff8801f7788380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[31908.558595]  ffff8801f7788400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

v2: Just leak the memory (8 bytes) as freeing it ourselves is not safe,
and we need to coordinate a proper fix in platform_device itself.

Fixes: eef57324d9 ("drm/i915: setup bridge for HDMI LPE audio driver")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99952
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: Jerome Anand <jerome.anand@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Takashi Iwai <tiwai@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20170412080251.30648-1-chris@chris-wilson.co.uk
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_lpe_audio.c

@@ -131,8 +131,15 @@ err:
 
 static void lpe_audio_platdev_destroy(struct drm_i915_private *dev_priv)
 {
+	/* XXX Note that platform_device_register_full() allocates a dma_mask
+	 * and never frees it. We can't free it here as we cannot guarantee
+	 * this is the last reference (i.e. that the dma_mask will not be
+	 * used after our unregister). So ee choose to leak the sizeof(u64)
+	 * allocation here - it should be fixed in the platform_device rather
+	 * than us fiddle with its internals.
+	 */
+
 	platform_device_unregister(dev_priv->lpe_audio.platdev);
-	kfree(dev_priv->lpe_audio.platdev->dev.dma_mask);
 }
 
 static void lpe_audio_irq_unmask(struct irq_data *d)