math: auditory: guard mod_psy_get_mel_filterbank() against zero divisors

The mel-bin loop in mod_psy_get_mel_filterbank() divides by delta_cl and
delta_rc on every FFT bin, and by (right_hz - left_hz) when slaney
normalization is enabled. With unusual configurations these denominators
can become zero or negative — for example when start_freq >= end_freq,
when the requested mel_bins is large enough that integer division
truncates the mel step to zero, or at extreme inputs where psy_mel_to_hz
saturates and right_hz no longer exceeds left_hz.

Reject such configurations explicitly. After computing mel_step, return
-EINVAL if it is not positive, which also covers both delta values
since they equal mel_step. In the slaney_normalize branch, also verify
right_hz > left_hz before computing the scale factor.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

Author: singalsu

src/math/auditory/auditory.c

@@ -149,6 +149,16 @@ int mod_psy_get_mel_filterbank(struct processing_module *mod, struct psy_mel_fil
 	mel_start = psy_hz_to_mel(fb->start_freq);
 	mel_end = psy_hz_to_mel(fb->end_freq);
 	mel_step = (mel_end - mel_start) / (fb->mel_bins + 1);
+	/* delta_cl / delta_rc below are both equal to mel_step; guard against
+	 * a non-positive step (start_freq >= end_freq, or so few bins that the
+	 * integer division truncates to zero) before using them as divisors.
+	 */
+	if (mel_step <= 0) {
+		comp_cl_err(mod->dev, "Invalid mel_step %d (start_freq=%d end_freq=%d mel_bins=%d)",
+			    mel_step, fb->start_freq, fb->end_freq, fb->mel_bins);
+		return -EINVAL;
+	}
+
 	for (i = 0; i < fb->mel_bins; i++) {
 		left_mel = mel_start + i * mel_step;
 		center_mel = mel_start + (i + 1) * mel_step;
@@ -160,6 +170,11 @@ int mod_psy_get_mel_filterbank(struct processing_module *mod, struct psy_mel_fil
 		if (fb->slaney_normalize) {
 			left_hz = psy_mel_to_hz(left_mel);
 			right_hz = psy_mel_to_hz(right_mel);
+			if (right_hz <= left_hz) {
+				comp_cl_err(mod->dev, "Invalid Hz range left=%d right=%d at mel bin %d",
+					    left_hz, right_hz, i);
+				return -EINVAL;
+			}
 			scale = Q_SHIFT_RND(TWO_Q29 / (right_hz - left_hz), 29, 16); /* Q16.16*/
 			if (i == 0) {
 				scale_inv = Q_SHIFT_LEFT(ONE_Q30 / scale, 14, 16);