avcodec/mjpegdec: Check input buffer size.

Fixes: Timeout
Fixes: 6381/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEGLS_fuzzer-5665032743419904

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

libavcodec/mjpegdec.c

@@ -335,6 +335,8 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
     av_log(s->avctx, AV_LOG_DEBUG, "sof0: picture: %dx%d\n", width, height);
     if (av_image_check_size(width, height, 0, s->avctx) < 0)
         return AVERROR_INVALIDDATA;
+    if (s->buf_size && (width + 7) / 8 * ((height + 7) / 8) > s->buf_size * 4LL)
+        return AVERROR_INVALIDDATA;
 
     nb_components = get_bits(&s->gb, 8);
     if (nb_components <= 0 ||
@@ -2247,6 +2249,8 @@ int ff_mjpeg_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     int ret = 0;
     int is16bit;
 
+    s->buf_size = buf_size;
+
     av_dict_free(&s->exif_metadata);
     av_freep(&s->stereo3d);
     s->adobe_transform = -1;

libavcodec/mjpegdec.h

@@ -47,6 +47,7 @@ typedef struct MJpegDecodeContext {
     AVClass *class;
     AVCodecContext *avctx;
     GetBitContext gb;
+    int buf_size;
 
     int start_code; /* current start code */
     int buffer_size;