ALSA: hda: ignore invalid NHLT table

On some Lenovo systems if the microphone is disabled in the BIOS
only the NHLT table header is created, with no data. This means
the endpoints field is not correctly set to zero - leading to an
unintialised variable and hence invalid descriptors are parsed
leading to page faults.

The Lenovo firmware team is addressing this, but adding a check
preventing invalid tables being parsed is worthwhile.

Tested on a Lenovo T14.
Tested-by: Philipp Leskovitz <philipp.leskovitz@secunet.com>
Reported-by: Philipp Leskovitz <philipp.leskovitz@secunet.com>
Signed-off-by: Mark Pearson <markpearson@lenovo.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210302141003.7342-1-markpearson@lenovo.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/hda/intel-nhlt.c

@@ -39,6 +39,11 @@ int intel_nhlt_get_dmic_geo(struct device *dev, struct nhlt_acpi_table *nhlt)
 	if (!nhlt)
 		return 0;
 
+	if (nhlt->header.length <= sizeof(struct acpi_table_header)) {
+		dev_warn(dev, "Invalid DMIC description table\n");
+		return 0;
+	}
+
 	for (j = 0, epnt = nhlt->desc; j < nhlt->endpoint_count; j++,
 	     epnt = (struct nhlt_endpoint *)((u8 *)epnt + epnt->length)) {