avcodec/zmbv: Check that the decompressed data size is correct

This checks the value exactly for intra frames and checks it against a
minimum for inter frames as they can be variable.

Fixes: Timeout
Fixes: 10182/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ZMBV_fuzzer-6245951174344704

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/zmbv.c

@@ -409,6 +409,7 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame, AVPac
     int zret = Z_OK; // Zlib return code
     int len = buf_size;
     int hi_ver, lo_ver, ret;
+    int expected_size;
 
     /* parse header */
     if (len < 1)
@@ -510,6 +511,14 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame, AVPac
         memset(c->prev, 0, avctx->width * avctx->height * (c->bpp / 8));
         c->decode_intra= decode_intra;
     }
+    if (c->flags & ZMBV_KEYFRAME) {
+        expected_size = avctx->width * avctx->height * (c->bpp / 8);
+    } else {
+        expected_size = (c->bx * c->by * 2 + 3) & ~3;
+    }
+    if (avctx->pix_fmt == AV_PIX_FMT_PAL8 &&
+        (c->flags & (ZMBV_DELTAPAL | ZMBV_KEYFRAME)))
+        expected_size += 768;
 
     if (!c->decode_intra) {
         av_log(avctx, AV_LOG_ERROR, "Error! Got no format or no keyframe!\n");
@@ -539,6 +548,11 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame, AVPac
         }
         c->decomp_len = c->zstream.total_out;
     }
+    if (expected_size > c->decomp_len ||
+        (c->flags & ZMBV_KEYFRAME) && expected_size < c->decomp_len) {
+        av_log(avctx, AV_LOG_ERROR, "decompressed size %d is incorrect, expected %d\n", c->decomp_len, expected_size);
+        return AVERROR_INVALIDDATA;
+    }
     if (c->flags & ZMBV_KEYFRAME) {
         frame->key_frame = 1;
         frame->pict_type = AV_PICTURE_TYPE_I;