ALSA: hda: Fix Oops by 9.1 surround channel names

get_line_out_pfx() may trigger an Oops by overflowing the static array
with more than 8 channels.  This was reported for MacBookPro 12,1 with
Cirrus codec.

As a workaround, extend for the 9.1 channels and also fix the
potential Oops by unifying the code paths accessing the same array
with the proper size check.

Reported-by: Olliver Schinagl <[email protected]>
Cc: <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

Author: tiwai

sound/pci/hda/hda_generic.c

@@ -1155,8 +1155,8 @@ static bool path_has_mixer(struct hda_codec *codec, int path_idx, int ctl_type)
 	return path && path->ctls[ctl_type];
 }
 
-static const char * const channel_name[4] = {
-	"Front", "Surround", "CLFE", "Side"
+static const char * const channel_name[] = {
+	"Front", "Surround", "CLFE", "Side", "Back",
 };
 
 /* give some appropriate ctl name prefix for the given line out channel */
@@ -1182,7 +1182,7 @@ static const char *get_line_out_pfx(struct hda_codec *codec, int ch,
 
 	/* multi-io channels */
 	if (ch >= cfg->line_outs)
-		return channel_name[ch];
+		goto fixed_name;
 
 	switch (cfg->line_out_type) {
 	case AUTO_PIN_SPEAKER_OUT:
@@ -1234,6 +1234,7 @@ static const char *get_line_out_pfx(struct hda_codec *codec, int ch,
 	if (cfg->line_outs == 1 && !spec->multi_ios)
 		return "Line Out";
 
+ fixed_name:
 	if (ch >= ARRAY_SIZE(channel_name)) {
 		snd_BUG();
 		return "PCM";