avcodec/bitstream: Check code length before truncating to uint8_t

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/bitstream.c

@@ -302,15 +302,17 @@ int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
     j = 0;
 #define COPY(condition)\
     for (i = 0; i < nb_codes; i++) {                                        \
-        GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);               \
+        unsigned len;                                                       \
+        GET_DATA(len, bits, i, bits_wrap, bits_size);                       \
         if (!(condition))                                                   \
             continue;                                                       \
-        if (buf[j].bits > 3*nb_bits || buf[j].bits>32) {                    \
-            av_log(NULL, AV_LOG_ERROR, "Too long VLC (%d) in init_vlc\n", buf[j].bits);\
+        if (len > 3*nb_bits || len > 32) {                                  \
+            av_log(NULL, AV_LOG_ERROR, "Too long VLC (%u) in init_vlc\n", len);\
             if (buf != localbuf)                                            \
                 av_free(buf);                                               \
             return AVERROR(EINVAL);                                         \
         }                                                                   \
+        buf[j].bits = len;                                                  \
         GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);            \
         if (buf[j].code >= (1LL<<buf[j].bits)) {                            \
             av_log(NULL, AV_LOG_ERROR, "Invalid code %"PRIx32" for %d in "  \
@@ -329,10 +331,10 @@ int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
             buf[j].symbol = i;                                              \
         j++;                                                                \
     }
-    COPY(buf[j].bits > nb_bits);
+    COPY(len > nb_bits);
     // qsort is the slowest part of init_vlc, and could probably be improved or avoided
     AV_QSORT(buf, j, struct VLCcode, compare_vlcspec);
-    COPY(buf[j].bits && buf[j].bits <= nb_bits);
+    COPY(len && len <= nb_bits);
     nb_codes = j;
 
     ret = build_table(vlc, nb_bits, nb_codes, buf, flags);