ALSA: core: Validate compress device numbers without dynamic minors

[ Upstream commit 796e119 ]

Without CONFIG_SND_DYNAMIC_MINORS, ALSA reserves only two fixed minors
for compress devices on each card: comprD0 and comprD1.

snd_find_free_minor() currently computes the compress minor as
type + dev without validating dev first, so device numbers greater than
1 spill into the HWDEP minor range instead of failing registration.

ASoC passes rtd->id to snd_compress_new(), so this can happen on real
non-dynamic-minor builds.

Add a dedicated fixed-minor check for SNDRV_DEVICE_TYPE_COMPRESS in
snd_find_free_minor() and reject out-of-range device numbers with
-EINVAL before constructing the minor.

Also remove the stale TODO in compress_offload.c that still claims
multiple compress nodes are missing.

Fixes: 3eafc95 ("ALSA: core: add support for compressed devices")
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260325-alsa-compress-static-minors-v1-1-0628573bee1c@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: CassivsGabriellis

sound/core/compress_offload.c

@@ -41,13 +41,6 @@
 #define COMPR_CODEC_CAPS_OVERFLOW
 #endif
 
-/* TODO:
- * - add substream support for multiple devices in case of
- *	SND_DYNAMIC_MINORS is not used
- * - Multiple node representation
- *	driver should be able to register multiple nodes
- */
-
 struct snd_compr_file {
 	unsigned long caps;
 	struct snd_compr_stream stream;

sound/core/sound.c

@@ -216,9 +216,16 @@ static int snd_find_free_minor(int type, struct snd_card *card, int dev)
 	case SNDRV_DEVICE_TYPE_RAWMIDI:
 	case SNDRV_DEVICE_TYPE_PCM_PLAYBACK:
 	case SNDRV_DEVICE_TYPE_PCM_CAPTURE:
+		if (snd_BUG_ON(!card))
+			return -EINVAL;
+		minor = SNDRV_MINOR(card->number, type + dev);
+		break;
 	case SNDRV_DEVICE_TYPE_COMPRESS:
 		if (snd_BUG_ON(!card))
 			return -EINVAL;
+		if (dev < 0 ||
+		    dev >= SNDRV_MINOR_HWDEP - SNDRV_MINOR_COMPRESS)
+			return -EINVAL;
 		minor = SNDRV_MINOR(card->number, type + dev);
 		break;
 	default: