avfilter/af_surround: Check output format

Fixes: CID1516994 Out-of-bounds access
Fixes: CID1516996 Out-of-bounds access
Fixes: CID1516999 Out-of-bounds access

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_surround.c

@@ -1123,6 +1123,31 @@ static av_cold int init(AVFilterContext *ctx)
     s->create_lfe = av_channel_layout_index_from_channel(&s->out_ch_layout,
                                                          AV_CHAN_LOW_FREQUENCY) >= 0;
 
+    switch (out_channel_layout) {
+    case AV_CH_LAYOUT_MONO:
+    case AV_CH_LAYOUT_STEREO:
+    case AV_CH_LAYOUT_2POINT1:
+    case AV_CH_LAYOUT_2_1:
+    case AV_CH_LAYOUT_2_2:
+    case AV_CH_LAYOUT_SURROUND:
+    case AV_CH_LAYOUT_3POINT1:
+    case AV_CH_LAYOUT_QUAD:
+    case AV_CH_LAYOUT_4POINT0:
+    case AV_CH_LAYOUT_4POINT1:
+    case AV_CH_LAYOUT_5POINT0:
+    case AV_CH_LAYOUT_5POINT1:
+    case AV_CH_LAYOUT_5POINT0_BACK:
+    case AV_CH_LAYOUT_5POINT1_BACK:
+    case AV_CH_LAYOUT_6POINT0:
+    case AV_CH_LAYOUT_6POINT1:
+    case AV_CH_LAYOUT_7POINT0:
+    case AV_CH_LAYOUT_7POINT1:
+    case AV_CH_LAYOUT_OCTAGONAL:
+        break;
+    default:
+        goto fail;
+    }
+
     switch (in_channel_layout) {
     case AV_CH_LAYOUT_STEREO:
         s->filter = filter_stereo;