interplayacm: check for too large b

This fixes out-of-bounds reads.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavcodec/interplayacm.c

@@ -326,6 +326,10 @@ static int t15(InterplayACMContext *s, unsigned ind, unsigned col)
     for (i = 0; i < s->rows; i++) {
         /* b = (x1) + (x2 * 3) + (x3 * 9) */
         b = get_bits(gb, 5);
+        if (b > 26) {
+            av_log(NULL, AV_LOG_ERROR, "Too large b = %d > 26\n", b);
+            return AVERROR_INVALIDDATA;
+        }
 
         n1 =  (mul_3x3[b] & 0x0F) - 1;
         n2 = ((mul_3x3[b] >> 4) & 0x0F) - 1;
@@ -351,6 +355,10 @@ static int t27(InterplayACMContext *s, unsigned ind, unsigned col)
     for (i = 0; i < s->rows; i++) {
         /* b = (x1) + (x2 * 5) + (x3 * 25) */
         b = get_bits(gb, 7);
+        if (b > 124) {
+            av_log(NULL, AV_LOG_ERROR, "Too large b = %d > 124\n", b);
+            return AVERROR_INVALIDDATA;
+        }
 
         n1 =  (mul_3x5[b] & 0x0F) - 2;
         n2 = ((mul_3x5[b] >> 4) & 0x0F) - 2;
@@ -375,6 +383,10 @@ static int t37(InterplayACMContext *s, unsigned ind, unsigned col)
     for (i = 0; i < s->rows; i++) {
         /* b = (x1) + (x2 * 11) */
         b = get_bits(gb, 7);
+        if (b > 120) {
+            av_log(NULL, AV_LOG_ERROR, "Too large b = %d > 120\n", b);
+            return AVERROR_INVALIDDATA;
+        }
 
         n1 =  (mul_2x11[b] & 0x0F) - 5;
         n2 = ((mul_2x11[b] >> 4) & 0x0F) - 5;