ffv1dec: check that global parameters do not change in version 0/1

Such changes are neither allowed nor supported

Found-by: ami_stuff
Bug-Id: CVE-2013-7020
CC: libav-stable@libav.org
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/ffv1dec.c

@@ -550,6 +550,7 @@ static int read_header(FFV1Context *f)
     memset(state, 128, sizeof(state));
 
     if (f->version < 2) {
+        int chroma_planes, chroma_h_shift, chroma_v_shift, transparency, colorspace, bits_per_raw_sample;
         unsigned v = get_symbol(c, state, 0);
         if (v > 1) {
             av_log(f->avctx, AV_LOG_ERROR,
@@ -566,15 +567,32 @@ static int read_header(FFV1Context *f)
                     get_symbol(c, state, 1) + c->one_state[i];
         }
 
-        f->colorspace = get_symbol(c, state, 0); //YUV cs type
+        colorspace          = get_symbol(c, state, 0); //YUV cs type
+        bits_per_raw_sample = f->version > 0 ? get_symbol(c, state, 0) : f->avctx->bits_per_raw_sample;
+        chroma_planes       = get_rac(c, state);
+        chroma_h_shift      = get_symbol(c, state, 0);
+        chroma_v_shift      = get_symbol(c, state, 0);
+        transparency        = get_rac(c, state);
+
+        if (f->plane_count) {
+            if (colorspace          != f->colorspace                 ||
+                bits_per_raw_sample != f->avctx->bits_per_raw_sample ||
+                chroma_planes       != f->chroma_planes              ||
+                chroma_h_shift      != f->chroma_h_shift             ||
+                chroma_v_shift      != f->chroma_v_shift             ||
+                transparency        != f->transparency) {
+                av_log(f->avctx, AV_LOG_ERROR, "Invalid change of global parameters\n");
+                return AVERROR_INVALIDDATA;
+            }
+        }
 
-        if (f->version > 0)
-            f->avctx->bits_per_raw_sample = get_symbol(c, state, 0);
+        f->colorspace                 = colorspace;
+        f->avctx->bits_per_raw_sample = bits_per_raw_sample;
+        f->chroma_planes              = chroma_planes;
+        f->chroma_h_shift             = chroma_h_shift;
+        f->chroma_v_shift             = chroma_v_shift;
+        f->transparency               = transparency;
 
-        f->chroma_planes  = get_rac(c, state);
-        f->chroma_h_shift = get_symbol(c, state, 0);
-        f->chroma_v_shift = get_symbol(c, state, 0);
-        f->transparency   = get_rac(c, state);
         f->plane_count    = 2 + f->transparency;
     }