lavc/vp9: fix reference frame dimensions check for SINGLE_REFERENCE mode

With the description in frame size with refs semantics (SPEC 7.2.5),
it is a requirement of bitstream conformance that for at least one
reference frame has the valid dimensions.

Modify the check to make sure the decoder works well in SINGLE_REFERENCE
mode that not all reference frames have valid dimensions.

Check and error out if invalid reference frame is used in inter_recon.

One of the failure case is a 480x272 inter frame (SINGLE_REFERENCE mode)
with following reference pool:

0.  960x544    LAST    valid
1. 1920x1088 GOLDEN  invalid, but not used in single reference mode
2. 1920x1088 ALTREF  invalid, but not used in single reference mode
3~7  ...     Unused

Identical logic in libvpx:
<https://github.com/webmproject/libvpx/blob/master/vp9/decoder/vp9_decodeframe.c#L736>

Signed-off-by: Linjie Fu <linjie.fu@intel.com>
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavcodec/vp9.c

@@ -804,6 +804,7 @@ static int decode_frame_header(AVCodecContext *avctx,
 
     /* check reference frames */
     if (!s->s.h.keyframe && !s->s.h.intraonly) {
+        int valid_ref_frame = 0;
         for (i = 0; i < 3; i++) {
             AVFrame *ref = s->s.refs[s->s.h.refidx[i]].f;
             int refw = ref->width, refh = ref->height;
@@ -817,17 +818,25 @@ static int decode_frame_header(AVCodecContext *avctx,
             } else if (refw == w && refh == h) {
                 s->mvscale[i][0] = s->mvscale[i][1] = 0;
             } else {
+                /* Check to make sure at least one of frames that */
+                /* this frame references has valid dimensions     */
                 if (w * 2 < refw || h * 2 < refh || w > 16 * refw || h > 16 * refh) {
-                    av_log(avctx, AV_LOG_ERROR,
+                    av_log(avctx, AV_LOG_WARNING,
                            "Invalid ref frame dimensions %dx%d for frame size %dx%d\n",
                            refw, refh, w, h);
-                    return AVERROR_INVALIDDATA;
+                    s->mvscale[i][0] = s->mvscale[i][1] = REF_INVALID_SCALE;
+                    continue;
                 }
                 s->mvscale[i][0] = (refw << 14) / w;
                 s->mvscale[i][1] = (refh << 14) / h;
                 s->mvstep[i][0] = 16 * s->mvscale[i][0] >> 14;
                 s->mvstep[i][1] = 16 * s->mvscale[i][1] >> 14;
             }
+            valid_ref_frame++;
+        }
+        if (!valid_ref_frame) {
+            av_log(avctx, AV_LOG_ERROR, "No valid reference frame is found, bitstream not supported\n");
+            return AVERROR_INVALIDDATA;
         }
     }
 
@@ -1622,6 +1631,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
             s->td[i].eob = s->td[i].eob_base;
             s->td[i].uveob[0] = s->td[i].uveob_base[0];
             s->td[i].uveob[1] = s->td[i].uveob_base[1];
+            s->td[i].error_info = 0;
         }
 
 #if HAVE_THREADS
@@ -1678,6 +1688,12 @@ FF_ENABLE_DEPRECATION_WARNINGS
     } while (s->pass++ == 1);
     ff_thread_report_progress(&s->s.frames[CUR_FRAME].tf, INT_MAX, 0);
 
+    if (s->td->error_info < 0) {
+        av_log(avctx, AV_LOG_ERROR, "Failed to decode tile data\n");
+        s->td->error_info = 0;
+        return AVERROR_INVALIDDATA;
+    }
+
 finish:
     // ref frame setup
     for (i = 0; i < 8; i++) {

libavcodec/vp9dec.h

@@ -36,6 +36,8 @@
 #include "vp9dsp.h"
 #include "vp9shared.h"
 
+#define REF_INVALID_SCALE 0xFFFF
+
 enum MVJoint {
     MV_JOINT_ZERO,
     MV_JOINT_H,
@@ -221,6 +223,9 @@ struct VP9TileData {
     struct { int x, y; } min_mv, max_mv;
     int16_t *block_base, *block, *uvblock_base[2], *uvblock[2];
     uint8_t *eob_base, *uveob_base[2], *eob, *uveob[2];
+
+    // error message
+    int error_info;
 };
 
 void ff_vp9_fill_mv(VP9TileData *td, VP56mv *mv, int mode, int sb);

libavcodec/vp9recon.c

@@ -572,6 +572,16 @@ static av_always_inline void inter_recon(VP9TileData *td, int bytesperpixel)
     VP9Block *b = td->b;
     int row = td->row, col = td->col;
 
+    if (s->mvscale[b->ref[0]][0] == REF_INVALID_SCALE ||
+        (b->comp && s->mvscale[b->ref[1]][0] == REF_INVALID_SCALE)) {
+        if (!s->td->error_info) {
+            s->td->error_info = AVERROR_INVALIDDATA;
+            av_log(NULL, AV_LOG_ERROR, "Bitstream not supported, "
+                                       "reference frame has invalid dimensions\n");
+        }
+        return;
+    }
+
     if (s->mvscale[b->ref[0]][0] || (b->comp && s->mvscale[b->ref[1]][0])) {
         if (bytesperpixel == 1) {
             inter_pred_scaled_8bpp(td);