Document and validate AVFrame plane pointers.

Check that the required plane pointers and only
those are set up.
Currently does not enforce anything for the palette
pointer of pseudopal formats as I am unsure about the
requirements.
Signed-off-by: NReimar Döffinger <Reimar.Doeffinger@gmx.de>

doc/APIchanges

@@ -15,6 +15,12 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2016-02-28 - xxxxxxx - lavc 57.27.101
+  Validate AVFrame returned by get_buffer2 to have required
+  planes not NULL and unused planes set to NULL as crashes
+  and buffer overflow are possible with certain streams if
+  that is not the case.
+
 2016-xx-xx - xxxxxxx - lavc 57.27.100 - avcodec.h
   "flags2" decoding option now allows the flag "ass_ro_flush_noop" preventing
   the reset of the ASS ReadOrder field on flush. This affects the content of

libavcodec/utils.c

@@ -853,6 +853,30 @@ int ff_decode_frame_props(AVCodecContext *avctx, AVFrame *frame)
     return ff_init_buffer_info(avctx, frame);
 }
 
+static void validate_avframe_allocation(AVCodecContext *avctx, AVFrame *frame)
+{
+    if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
+        int i;
+        int num_planes = av_pix_fmt_count_planes(frame->format);
+        const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(frame->format);
+        int flags = desc ? desc->flags : 0;
+        if (num_planes == 1 && (flags & AV_PIX_FMT_FLAG_PAL))
+            num_planes = 2;
+        for (i = 0; i < num_planes; i++) {
+            av_assert0(frame->data[i]);
+        }
+        // For now do not enforce anything for palette of pseudopal formats
+        if (num_planes == 1 && (flags & AV_PIX_FMT_FLAG_PSEUDOPAL))
+            num_planes = 2;
+        // For formats without data like hwaccel allow unused pointers to be non-NULL.
+        for (i = num_planes; num_planes > 0 && i < FF_ARRAY_ELEMS(frame->data); i++) {
+            if (frame->data[i])
+                av_log(avctx, AV_LOG_ERROR, "Buffer returned by get_buffer2() did not zero unused plane pointers\n");
+            frame->data[i] = NULL;
+        }
+    }
+}
+
 static int get_buffer_internal(AVCodecContext *avctx, AVFrame *frame, int flags)
 {
     const AVHWAccel *hwaccel = avctx->hwaccel;
@@ -889,6 +913,8 @@ static int get_buffer_internal(AVCodecContext *avctx, AVFrame *frame, int flags)
         avctx->sw_pix_fmt = avctx->pix_fmt;
 
     ret = avctx->get_buffer2(avctx, frame, flags);
+    if (ret >= 0)
+        validate_avframe_allocation(avctx, frame);
 
 end:
     if (avctx->codec_type == AVMEDIA_TYPE_VIDEO && !override_dimensions) {

libavcodec/version.h

@@ -29,7 +29,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR  57
 #define LIBAVCODEC_VERSION_MINOR  27
-#define LIBAVCODEC_VERSION_MICRO 100
+#define LIBAVCODEC_VERSION_MICRO 101
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \

libavutil/frame.h

@@ -187,6 +187,9 @@ typedef struct AVFrame {
      * see avcodec_align_dimensions2(). Some filters and swscale can read
      * up to 16 bytes beyond the planes, if these filters are to be used,
      * then 16 extra bytes must be allocated.
+     *
+     * NOTE: Except for hwaccel formats, pointers not needed by the format
+     * MUST be set to NULL.
      */
     uint8_t *data[AV_NUM_DATA_POINTERS];