vorbis: Avoid some out-of-bounds reads

Fixes Bug: #190
Chromium Bug: #100543
Related to CVE-2011-3893
Signed-off-by: Reinhard Tartler <siretart@tauware.de>

libavcodec/vorbis.c

@@ -152,7 +152,7 @@ void ff_vorbis_ready_floor1_list(vorbis_floor1_entry * list, int values)
     }
 }
 
-static inline void render_line_unrolled(intptr_t x, intptr_t y, int x1,
+static inline void render_line_unrolled(intptr_t x, uint8_t y, int x1,
                                         intptr_t sy, int ady, int adx,
                                         float *buf)
 {
@@ -175,7 +175,7 @@ static inline void render_line_unrolled(intptr_t x, intptr_t y, int x1,
     }
 }
 
-static void render_line(int x0, int y0, int x1, int y1, float *buf)
+static void render_line(int x0, uint8_t y0, int x1, int y1, float *buf)
 {
     int dy  = y1 - y0;
     int adx = x1 - x0;
@@ -185,10 +185,10 @@ static void render_line(int x0, int y0, int x1, int y1, float *buf)
     if (ady*2 <= adx) { // optimized common case
         render_line_unrolled(x0, y0, x1, sy, ady, adx, buf);
     } else {
-        int base = dy / adx;
-        int x    = x0;
-        int y    = y0;
-        int err  = -adx;
+        int base  = dy / adx;
+        int x     = x0;
+        uint8_t y = y0;
+        int err   = -adx;
         ady -= FFABS(base) * adx;
         while (++x < x1) {
             y += base;
@@ -206,7 +206,8 @@ void ff_vorbis_floor1_render_list(vorbis_floor1_entry * list, int values,
                                   uint16_t *y_list, int *flag,
                                   int multiplier, float *out, int samples)
 {
-    int lx, ly, i;
+    int lx, i;
+    uint8_t ly;
     lx = 0;
     ly = y_list[0] * multiplier;
     for (i = 1; i < values; i++) {