indeo5dec: Make sure we have had a valid gop header.

This prevents decoding happening on a half initialized context.

Fixes CVE-2012-2779

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/indeo5.c

@@ -304,8 +304,12 @@ static int decode_pic_hdr(IVI45DecContext *ctx, AVCodecContext *avctx)
     ctx->frame_num = get_bits(&ctx->gb, 8);
 
     if (ctx->frame_type == FRAMETYPE_INTRA) {
-        if (decode_gop_header(ctx, avctx))
-            return -1;
+        ctx->gop_invalid = 1;
+        if (decode_gop_header(ctx, avctx)) {
+            av_log(avctx, AV_LOG_ERROR, "Invalid GOP header, skipping frames.\n");
+            return AVERROR_INVALIDDATA;
+        }
+        ctx->gop_invalid = 0;
     }
 
     if (ctx->frame_type != FRAMETYPE_NULL) {

libavcodec/ivi_common.c

@@ -739,6 +739,8 @@ int ff_ivi_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
                "Error while decoding picture header: %d\n", result);
         return -1;
     }
+    if (ctx->gop_invalid)
+        return AVERROR_INVALIDDATA;
 
     if (ctx->gop_flags & IVI5_IS_PROTECTED) {
         av_log(avctx, AV_LOG_ERROR, "Password-protected clip!\n");

libavcodec/ivi_common.h

@@ -248,6 +248,8 @@ typedef struct IVI45DecContext {
     int             (*decode_mb_info)  (struct IVI45DecContext *ctx, IVIBandDesc *band, IVITile *tile, AVCodecContext *avctx);
     void            (*switch_buffers)  (struct IVI45DecContext *ctx);
     int             (*is_nonnull_frame)(struct IVI45DecContext *ctx);
+
+    int gop_invalid;
 } IVI45DecContext;
 
 /** compare some properties of two pictures */