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voc: abort if channel count or sample format changes [bug #265]

A corrupted file can have blocks with differing values for channel
count or sample format.  Detect this and abort.

--- a/src/voc.c

+++ b/src/voc.c

@@ -168,9 +168,9 @@

   long srate;                   /* rate code (byte) of silence */

   size_t blockseek;         /* start of current output block */

   long samples;                 /* number of samples output */

-  uint16_t format;              /* VOC audio format */

+  int format;                   /* VOC audio format */

   int size;                     /* word length of data */

-  unsigned char channels;       /* number of sound channels */

+  int channels;                 /* number of sound channels */

   long total_size;              /* total size of all audio in file */

   int extended;                 /* Has an extended block been read? */

   adpcm_t adpcm;

@@ -238,6 +238,8 @@

     lsx_readb(ft, &uc);

   v->rate = -1;

+  v->format = -1;

+  v->channels = -1;

   v->block_remaining = 0;

   v->total_size = 0;    /* ANN added */

   v->extended = 0;

@@ -552,6 +554,7 @@

 {

   priv_t * v = (priv_t *) ft->priv;

   unsigned char uc, block;

+  uint16_t u16;

   sox_uint24_t sblen;

   uint16_t new_rate_16;

   uint32_t new_rate_32;

@@ -593,9 +596,17 @@

           }

           v->rate = uc;

           ft->signal.rate = 1000000.0 / (256 - v->rate);

+          if (v->channels != -1 && v->channels != 1) {

+            lsx_fail_errno(ft, SOX_EFMT, "channel count changed");

+            return SOX_EOF;

+          }

           v->channels = 1;

         }

         lsx_readb(ft, &uc);

+        if (v->format != -1 && uc != v->format) {

+          lsx_fail_errno(ft, SOX_EFMT, "format changed");

+          return SOX_EOF;

+        }

         v->format = uc;

         v->extended = 0;

         v->block_remaining = sblen - 2;

@@ -615,8 +626,18 @@

         ft->signal.rate = new_rate_32;

         lsx_readb(ft, &uc);

         v->size = uc;

-        lsx_readb(ft, &(v->channels));

-        lsx_readw(ft, &(v->format));    /* ANN: added format */

+        lsx_readb(ft, &uc);

+        if (v->channels != -1 && uc != v->channels) {

+          lsx_fail_errno(ft, SOX_EFMT, "channel count changed");

+          return SOX_EOF;

+        }

+        v->channels = uc;

+        lsx_readw(ft, &u16);    /* ANN: added format */

+        if (v->format != -1 && u16 != v->format) {

+          lsx_fail_errno(ft, SOX_EFMT, "format changed");

+          return SOX_EOF;

+        }

+        v->format = u16;

         lsx_skipbytes(ft, (size_t) 4);

         v->block_remaining = sblen - 12;

         return (SOX_SUCCESS);

@@ -698,6 +719,11 @@

         v->rate = new_rate_16;

         lsx_readb(ft, &uc); /* bits_per_sample */

         lsx_readb(ft, &uc);

+        if (v->channels != -1 && uc != v->channels) {

+          lsx_fail_errno(ft, SOX_EFMT, "channel count changed");

+          return SOX_EOF;

+        }

+        v->channels = uc;

         ft->signal.channels = uc? 2 : 1;      /* Stereo */

         /* Needed number of channels before finishing

          * compute for rate */