ALSA: hda - fix read before array start

UBSAN reports the following warning from accessing path->path[-1]
in set_path_power():

[   16.078040] ================================================================================
[   16.078124] UBSAN: Undefined behaviour in sound/pci/hda/hda_generic.c:3981:17
[   16.078198] index -1 is out of range for type 'hda_nid_t [10]'
[   16.078270] CPU: 2 PID: 1738 Comm: modprobe Not tainted 4.7.0-rc1-wt+ #47
[   16.078274] Hardware name: LENOVO 3443CTO/3443CTO, BIOS G6ET23WW (1.02 ) 08/14/2012
[   16.078278]  ffff8800cb246000 ffff8800cb3638b8 ffffffff815c4fe3 0000000000000032
[   16.078286]  ffff8800cb3638e0 ffffffffffffffff ffff8800cb3638d0 ffffffff8162443d
[   16.078294]  ffffffffa0894200 ffff8800cb363920 ffffffff81624af7 0000000000000292
[   16.078302] Call Trace:
[   16.078311]  [<ffffffff815c4fe3>] dump_stack+0x86/0xd3
[   16.078317]  [<ffffffff8162443d>] ubsan_epilogue+0xd/0x40
[   16.078324]  [<ffffffff81624af7>] __ubsan_handle_out_of_bounds+0x67/0x70
[   16.078335]  [<ffffffffa087665f>] set_path_power+0x1bf/0x230 [snd_hda_codec_generic]
[   16.078344]  [<ffffffffa087880d>] add_pin_power_ctls+0x8d/0xc0 [snd_hda_codec_generic]
[   16.078352]  [<ffffffffa087f190>] ? pin_power_down_callback+0x20/0x20 [snd_hda_codec_generic]
[   16.078360]  [<ffffffffa0878947>] add_all_pin_power_ctls+0x107/0x150 [snd_hda_codec_generic]
[   16.078370]  [<ffffffffa08842b3>] snd_hda_gen_parse_auto_config+0x2d73/0x49e0 [snd_hda_codec_generic]
[   16.078376]  [<ffffffff81173360>] ? trace_hardirqs_on_caller+0x1b0/0x2c0
[   16.078390]  [<ffffffffa089df27>] alc_parse_auto_config+0x147/0x310 [snd_hda_codec_realtek]
[   16.078402]  [<ffffffffa08a332a>] patch_alc269+0x23a/0x560 [snd_hda_codec_realtek]
[   16.078417]  [<ffffffffa0838644>] hda_codec_driver_probe+0xa4/0x1a0 [snd_hda_codec]
[   16.078424]  [<ffffffff817bbac1>] driver_probe_device+0x101/0x380
[   16.078430]  [<ffffffff817bbdf9>] __driver_attach+0xb9/0x100
[   16.078438]  [<ffffffff817bbd40>] ? driver_probe_device+0x380/0x380
[   16.078444]  [<ffffffff817b8d20>] bus_for_each_dev+0x70/0xc0
[   16.078449]  [<ffffffff817bb087>] driver_attach+0x27/0x50
[   16.078454]  [<ffffffff817ba956>] bus_add_driver+0x166/0x2c0
[   16.078460]  [<ffffffffa0369000>] ? 0xffffffffa0369000
[   16.078465]  [<ffffffff817bd13d>] driver_register+0x7d/0x130
[   16.078477]  [<ffffffffa083816f>] __hda_codec_driver_register+0x6f/0x90 [snd_hda_codec]
[   16.078488]  [<ffffffffa036901e>] realtek_driver_init+0x1e/0x1000 [snd_hda_codec_realtek]
[   16.078493]  [<ffffffff8100215e>] do_one_initcall+0x4e/0x1d0
[   16.078499]  [<ffffffff8119f54d>] ? rcu_read_lock_sched_held+0x6d/0x80
[   16.078504]  [<ffffffff813701b1>] ? kmem_cache_alloc_trace+0x391/0x560
[   16.078510]  [<ffffffff812bb314>] ? do_init_module+0x28/0x273
[   16.078515]  [<ffffffff812bb387>] do_init_module+0x9b/0x273
[   16.078522]  [<ffffffff811e3782>] load_module+0x20b2/0x3410
[   16.078527]  [<ffffffff811df140>] ? m_show+0x210/0x210
[   16.078533]  [<ffffffff813b2b26>] ? kernel_read+0x66/0xe0
[   16.078541]  [<ffffffff811e4cfa>] SYSC_finit_module+0xba/0xc0
[   16.078547]  [<ffffffff811e4d1e>] SyS_finit_module+0xe/0x10
[   16.078552]  [<ffffffff81a860fc>] entry_SYSCALL_64_fastpath+0x1f/0xbd
[   16.078556] ================================================================================

Fix by checking path->depth before use.
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_generic.c

@@ -3977,6 +3977,8 @@ static hda_nid_t set_path_power(struct hda_codec *codec, hda_nid_t nid,
 
 	for (n = 0; n < spec->paths.used; n++) {
 		path = snd_array_elem(&spec->paths, n);
+		if (!path->depth)
+			continue;
 		if (path->path[0] == nid ||
 		    path->path[path->depth - 1] == nid) {
 			bool pin_old = path->pin_enabled;