ASoC: wm_adsp: Fix validation of firmware and coeff lengths

The checks for whether another region/block header could be present
are subtracting the size from the current offset.  Obviously we should
instead subtract the offset from the size.

The checks for whether the region/block data fit in the file are
adding the data size to the current offset and header size, without
checking for integer overflow.  Rearrange these so that overflow is
impossible.
Signed-off-by: NBen Hutchings <ben.hutchings@codethink.co.uk>
Acked-by: NCharles Keepax <ckeepax@opensource.cirrus.com>
Tested-by: NCharles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: NMark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

sound/soc/codecs/wm_adsp.c

@@ -1733,7 +1733,7 @@ static int wm_adsp_load(struct wm_adsp *dsp)
 		 le64_to_cpu(footer->timestamp));
 
 	while (pos < firmware->size &&
-	       pos - firmware->size > sizeof(*region)) {
+	       sizeof(*region) < firmware->size - pos) {
 		region = (void *)&(firmware->data[pos]);
 		region_name = "Unknown";
 		reg = 0;
@@ -1782,8 +1782,8 @@ static int wm_adsp_load(struct wm_adsp *dsp)
 			 regions, le32_to_cpu(region->len), offset,
 			 region_name);
 
-		if ((pos + le32_to_cpu(region->len) + sizeof(*region)) >
-		    firmware->size) {
+		if (le32_to_cpu(region->len) >
+		    firmware->size - pos - sizeof(*region)) {
 			adsp_err(dsp,
 				 "%s.%d: %s region len %d bytes exceeds file length %zu\n",
 				 file, regions, region_name,
@@ -2253,7 +2253,7 @@ static int wm_adsp_load_coeff(struct wm_adsp *dsp)
 
 	blocks = 0;
 	while (pos < firmware->size &&
-	       pos - firmware->size > sizeof(*blk)) {
+	       sizeof(*blk) < firmware->size - pos) {
 		blk = (void *)(&firmware->data[pos]);
 
 		type = le16_to_cpu(blk->type);
@@ -2327,8 +2327,8 @@ static int wm_adsp_load_coeff(struct wm_adsp *dsp)
 		}
 
 		if (reg) {
-			if ((pos + le32_to_cpu(blk->len) + sizeof(*blk)) >
-			    firmware->size) {
+			if (le32_to_cpu(blk->len) >
+			    firmware->size - pos - sizeof(*blk)) {
 				adsp_err(dsp,
 					 "%s.%d: %s region len %d bytes exceeds file length %zu\n",
 					 file, blocks, region_name,