From 05de6e0ddc2c911b725955d2af331ffd76aa8186 Mon Sep 17 00:00:00 2001
From: Kurt Roeckx <kurt@roeckx.be>
Date: Sun, 28 Jan 2018 19:26:36 +0100
Subject: [PATCH] Check the size before reading with mad_bit_read

There are various cases where it attemps to read past the end of the buffer
using mad_bit_read(). Most functions didn't even know the size of the buffer
they were reading from.

Source: https://salsa.debian.org/multimedia-team/libmad/-/raw/debian/0.15.1b-11/debian/patches/length-check.patch?ref_type=tags

CVE: CVE-2017-8374
Upstream-Status: Inactive-Upstream [lastrelease: 2018]
Signed-off-by: Peter Marko <peter.marko@siemens.com>
---
 bit.c     |   3 +
 frame.c   |  20 +++++-
 layer12.c | 112 +++++++++++++++++++++++++++---
 layer3.c  | 198 ++++++++++++++++++++++++++++++++++++++----------------
 4 files changed, 262 insertions(+), 71 deletions(-)

diff --git a/bit.c b/bit.c
index c2bfb24..39ef50b 100644
--- a/bit.c
+++ b/bit.c
@@ -138,6 +138,9 @@ unsigned long mad_bit_read(struct mad_bitptr *bitptr, unsigned int len)
 {
   register unsigned long value;
 
+  if (len == 0)
+    return 0;
+
   if (bitptr->left == CHAR_BIT)
     bitptr->cache = *bitptr->byte;
 
diff --git a/frame.c b/frame.c
index 0cb3d0f..4b3aea8 100644
--- a/frame.c
+++ b/frame.c
@@ -120,11 +120,18 @@ static
 int decode_header(struct mad_header *header, struct mad_stream *stream)
 {
   unsigned int index;
+  struct mad_bitptr bufend_ptr;
 
   header->flags        = 0;
   header->private_bits = 0;
 
+  mad_bit_init(&bufend_ptr, stream->bufend);
+
   /* header() */
+  if (mad_bit_length(&stream->ptr, &bufend_ptr) < 32) {
+    stream->error = MAD_ERROR_BUFLEN;
+    return -1;
+  }
 
   /* syncword */
   mad_bit_skip(&stream->ptr, 11);
@@ -225,8 +232,13 @@ int decode_header(struct mad_header *header, struct mad_stream *stream)
   /* error_check() */
 
   /* crc_check */
-  if (header->flags & MAD_FLAG_PROTECTION)
+  if (header->flags & MAD_FLAG_PROTECTION) {
+    if (mad_bit_length(&stream->ptr, &bufend_ptr) < 16) {
+      stream->error = MAD_ERROR_BUFLEN;
+      return -1;
+    }
     header->crc_target = mad_bit_read(&stream->ptr, 16);
+  }
 
   return 0;
 }
@@ -338,7 +350,7 @@ int mad_header_decode(struct mad_header *header, struct mad_stream *stream)
       stream->error = MAD_ERROR_BUFLEN;
       goto fail;
     }
-    else if (!(ptr[0] == 0xff && (ptr[1] & 0xe0) == 0xe0)) {
+    else if ((end - ptr >= 2) && !(ptr[0] == 0xff && (ptr[1] & 0xe0) == 0xe0)) {
       /* mark point where frame sync word was expected */
       stream->this_frame = ptr;
       stream->next_frame = ptr + 1;
@@ -361,6 +373,8 @@ int mad_header_decode(struct mad_header *header, struct mad_stream *stream)
     ptr = mad_bit_nextbyte(&stream->ptr);
   }
 
+  stream->error = MAD_ERROR_NONE;
+
   /* begin processing */
   stream->this_frame = ptr;
   stream->next_frame = ptr + 1;  /* possibly bogus sync word */
@@ -413,7 +427,7 @@ int mad_header_decode(struct mad_header *header, struct mad_stream *stream)
     /* check that a valid frame header follows this frame */
 
     ptr = stream->next_frame;
-    if (!(ptr[0] == 0xff && (ptr[1] & 0xe0) == 0xe0)) {
+    if ((end - ptr >= 2) && !(ptr[0] == 0xff && (ptr[1] & 0xe0) == 0xe0)) {
       ptr = stream->next_frame = stream->this_frame + 1;
       goto sync;
     }
diff --git a/layer12.c b/layer12.c
index 6981f9c..b6f4a2f 100644
--- a/layer12.c
+++ b/layer12.c
@@ -72,10 +72,18 @@ mad_fixed_t const linear_table[14] = {
  * DESCRIPTION:	decode one requantized Layer I sample from a bitstream
  */
 static
-mad_fixed_t I_sample(struct mad_bitptr *ptr, unsigned int nb)
+mad_fixed_t I_sample(struct mad_bitptr *ptr, unsigned int nb, struct mad_stream *stream)
 {
   mad_fixed_t sample;
+  struct mad_bitptr frameend_ptr;
 
+  mad_bit_init(&frameend_ptr, stream->next_frame);
+
+  if (mad_bit_length(ptr, &frameend_ptr) < nb) {
+    stream->error = MAD_ERROR_LOSTSYNC;
+    stream->sync = 0;
+    return 0;
+  }
   sample = mad_bit_read(ptr, nb);
 
   /* invert most significant bit, extend sign, then scale to fixed format */
@@ -106,6 +114,10 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
   struct mad_header *header = &frame->header;
   unsigned int nch, bound, ch, s, sb, nb;
   unsigned char allocation[2][32], scalefactor[2][32];
+  struct mad_bitptr bufend_ptr, frameend_ptr;
+
+  mad_bit_init(&bufend_ptr, stream->bufend);
+  mad_bit_init(&frameend_ptr, stream->next_frame);
 
   nch = MAD_NCHANNELS(header);
 
@@ -118,6 +130,11 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
   /* check CRC word */
 
   if (header->flags & MAD_FLAG_PROTECTION) {
+    if (mad_bit_length(&stream->ptr, &bufend_ptr)
+		< 4 * (bound * nch + (32 - bound))) {
+      stream->error = MAD_ERROR_BADCRC;
+      return -1;
+    }
     header->crc_check =
       mad_bit_crc(stream->ptr, 4 * (bound * nch + (32 - bound)),
 		  header->crc_check);
@@ -133,6 +150,11 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
 
   for (sb = 0; sb < bound; ++sb) {
     for (ch = 0; ch < nch; ++ch) {
+      if (mad_bit_length(&stream->ptr, &frameend_ptr) < 4) {
+	stream->error = MAD_ERROR_LOSTSYNC;
+	stream->sync = 0;
+	return -1;
+      }
       nb = mad_bit_read(&stream->ptr, 4);
 
       if (nb == 15) {
@@ -145,6 +167,11 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
   }
 
   for (sb = bound; sb < 32; ++sb) {
+    if (mad_bit_length(&stream->ptr, &frameend_ptr) < 4) {
+      stream->error = MAD_ERROR_LOSTSYNC;
+      stream->sync = 0;
+      return -1;
+    }
     nb = mad_bit_read(&stream->ptr, 4);
 
     if (nb == 15) {
@@ -161,6 +188,11 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
   for (sb = 0; sb < 32; ++sb) {
     for (ch = 0; ch < nch; ++ch) {
       if (allocation[ch][sb]) {
+        if (mad_bit_length(&stream->ptr, &frameend_ptr) < 6) {
+	  stream->error = MAD_ERROR_LOSTSYNC;
+	  stream->sync = 0;
+	  return -1;
+	}
 	scalefactor[ch][sb] = mad_bit_read(&stream->ptr, 6);
 
 # if defined(OPT_STRICT)
@@ -185,8 +217,10 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
       for (ch = 0; ch < nch; ++ch) {
 	nb = allocation[ch][sb];
 	frame->sbsample[ch][s][sb] = nb ?
-	  mad_f_mul(I_sample(&stream->ptr, nb),
+	  mad_f_mul(I_sample(&stream->ptr, nb, stream),
 		    sf_table[scalefactor[ch][sb]]) : 0;
+	if (stream->error != 0)
+	  return -1;
       }
     }
 
@@ -194,7 +228,14 @@ int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
       if ((nb = allocation[0][sb])) {
 	mad_fixed_t sample;
 
-	sample = I_sample(&stream->ptr, nb);
+	if (mad_bit_length(&stream->ptr, &frameend_ptr) < nb) {
+	  stream->error = MAD_ERROR_LOSTSYNC;
+	  stream->sync = 0;
+          return -1;
+	}
+	sample = I_sample(&stream->ptr, nb, stream);
+        if (stream->error != 0)
+	  return -1;
 
 	for (ch = 0; ch < nch; ++ch) {
 	  frame->sbsample[ch][s][sb] =
@@ -280,13 +321,21 @@ struct quantclass {
 static
 void II_samples(struct mad_bitptr *ptr,
 		struct quantclass const *quantclass,
-		mad_fixed_t output[3])
+		mad_fixed_t output[3], struct mad_stream *stream)
 {
   unsigned int nb, s, sample[3];
+  struct mad_bitptr frameend_ptr;
+
+  mad_bit_init(&frameend_ptr, stream->next_frame);
 
   if ((nb = quantclass->group)) {
     unsigned int c, nlevels;
 
+    if (mad_bit_length(ptr, &frameend_ptr) < quantclass->bits) {
+      stream->error = MAD_ERROR_LOSTSYNC;
+      stream->sync = 0;
+      return;
+    }
     /* degrouping */
     c = mad_bit_read(ptr, quantclass->bits);
     nlevels = quantclass->nlevels;
@@ -299,8 +348,14 @@ void II_samples(struct mad_bitptr *ptr,
   else {
     nb = quantclass->bits;
 
-    for (s = 0; s < 3; ++s)
+    for (s = 0; s < 3; ++s) {
+      if (mad_bit_length(ptr, &frameend_ptr) < nb) {
+	stream->error = MAD_ERROR_LOSTSYNC;
+	stream->sync = 0;
+	return;
+      }
       sample[s] = mad_bit_read(ptr, nb);
+    }
   }
 
   for (s = 0; s < 3; ++s) {
@@ -336,6 +391,9 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
   unsigned char const *offsets;
   unsigned char allocation[2][32], scfsi[2][32], scalefactor[2][32][3];
   mad_fixed_t samples[3];
+  struct mad_bitptr frameend_ptr;
+
+  mad_bit_init(&frameend_ptr, stream->next_frame);
 
   nch = MAD_NCHANNELS(header);
 
@@ -402,13 +460,24 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
   for (sb = 0; sb < bound; ++sb) {
     nbal = bitalloc_table[offsets[sb]].nbal;
 
-    for (ch = 0; ch < nch; ++ch)
+    for (ch = 0; ch < nch; ++ch) {
+      if (mad_bit_length(&stream->ptr, &frameend_ptr) < nbal) {
+	stream->error = MAD_ERROR_LOSTSYNC;
+	stream->sync = 0;
+	return -1;
+      }
       allocation[ch][sb] = mad_bit_read(&stream->ptr, nbal);
+    }
   }
 
   for (sb = bound; sb < sblimit; ++sb) {
     nbal = bitalloc_table[offsets[sb]].nbal;
 
+    if (mad_bit_length(&stream->ptr, &frameend_ptr) < nbal) {
+      stream->error = MAD_ERROR_LOSTSYNC;
+      stream->sync = 0;
+      return -1;
+    }
     allocation[0][sb] =
     allocation[1][sb] = mad_bit_read(&stream->ptr, nbal);
   }
@@ -417,8 +486,14 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
 
   for (sb = 0; sb < sblimit; ++sb) {
     for (ch = 0; ch < nch; ++ch) {
-      if (allocation[ch][sb])
+      if (allocation[ch][sb]) {
+	if (mad_bit_length(&stream->ptr, &frameend_ptr) < 2) {
+	  stream->error = MAD_ERROR_LOSTSYNC;
+	  stream->sync = 0;
+	  return -1;
+	}
 	scfsi[ch][sb] = mad_bit_read(&stream->ptr, 2);
+      }
     }
   }
 
@@ -441,6 +516,11 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
   for (sb = 0; sb < sblimit; ++sb) {
     for (ch = 0; ch < nch; ++ch) {
       if (allocation[ch][sb]) {
+	if (mad_bit_length(&stream->ptr, &frameend_ptr) < 6) {
+	  stream->error = MAD_ERROR_LOSTSYNC;
+	  stream->sync = 0;
+	  return -1;
+	}
 	scalefactor[ch][sb][0] = mad_bit_read(&stream->ptr, 6);
 
 	switch (scfsi[ch][sb]) {
@@ -451,11 +531,21 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
 	  break;
 
 	case 0:
+	  if (mad_bit_length(&stream->ptr, &frameend_ptr) < 6) {
+	    stream->error = MAD_ERROR_LOSTSYNC;
+	    stream->sync = 0;
+	    return -1;
+	  }
 	  scalefactor[ch][sb][1] = mad_bit_read(&stream->ptr, 6);
 	  /* fall through */
 
 	case 1:
 	case 3:
+	  if (mad_bit_length(&stream->ptr, &frameend_ptr) < 6) {
+	    stream->error = MAD_ERROR_LOSTSYNC;
+	    stream->sync = 0;
+	    return -1;
+	  }
 	  scalefactor[ch][sb][2] = mad_bit_read(&stream->ptr, 6);
 	}
 
@@ -487,7 +577,9 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
 	if ((index = allocation[ch][sb])) {
 	  index = offset_table[bitalloc_table[offsets[sb]].offset][index - 1];
 
-	  II_samples(&stream->ptr, &qc_table[index], samples);
+	  II_samples(&stream->ptr, &qc_table[index], samples, stream);
+	  if (stream->error != 0)
+            return -1;
 
 	  for (s = 0; s < 3; ++s) {
 	    frame->sbsample[ch][3 * gr + s][sb] =
@@ -505,7 +597,9 @@ int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
       if ((index = allocation[0][sb])) {
 	index = offset_table[bitalloc_table[offsets[sb]].offset][index - 1];
 
-	II_samples(&stream->ptr, &qc_table[index], samples);
+	II_samples(&stream->ptr, &qc_table[index], samples, stream);
+	if (stream->error != 0)
+          return -1;
 
 	for (ch = 0; ch < nch; ++ch) {
 	  for (s = 0; s < 3; ++s) {
diff --git a/layer3.c b/layer3.c
index 7dc4ca6..59a81ed 100644
--- a/layer3.c
+++ b/layer3.c
@@ -598,7 +598,8 @@ enum mad_error III_sideinfo(struct mad_bitptr *ptr, unsigned int nch,
 static
 unsigned int III_scalefactors_lsf(struct mad_bitptr *ptr,
 				  struct channel *channel,
-				  struct channel *gr1ch, int mode_extension)
+				  struct channel *gr1ch, int mode_extension,
+				  unsigned int bits_left, unsigned int *part2_length)
 {
   struct mad_bitptr start;
   unsigned int scalefac_compress, index, slen[4], part, n, i;
@@ -644,8 +645,12 @@ unsigned int III_scalefactors_lsf(struct mad_bitptr *ptr,
 
     n = 0;
     for (part = 0; part < 4; ++part) {
-      for (i = 0; i < nsfb[part]; ++i)
+      for (i = 0; i < nsfb[part]; ++i) {
+	if (bits_left < slen[part])
+	  return MAD_ERROR_BADSCFSI;
 	channel->scalefac[n++] = mad_bit_read(ptr, slen[part]);
+	bits_left -= slen[part];
+      }
     }
 
     while (n < 39)
@@ -690,7 +695,10 @@ unsigned int III_scalefactors_lsf(struct mad_bitptr *ptr,
       max = (1 << slen[part]) - 1;
 
       for (i = 0; i < nsfb[part]; ++i) {
+	if (bits_left < slen[part])
+	  return MAD_ERROR_BADSCFSI;
 	is_pos = mad_bit_read(ptr, slen[part]);
+	bits_left -= slen[part];
 
 	channel->scalefac[n] = is_pos;
 	gr1ch->scalefac[n++] = (is_pos == max);
@@ -703,7 +711,8 @@ unsigned int III_scalefactors_lsf(struct mad_bitptr *ptr,
     }
   }
 
-  return mad_bit_length(&start, ptr);
+  *part2_length = mad_bit_length(&start, ptr);
+  return MAD_ERROR_NONE;
 }
 
 /*
@@ -712,7 +721,8 @@ unsigned int III_scalefactors_lsf(struct mad_bitptr *ptr,
  */
 static
 unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
-			      struct channel const *gr0ch, unsigned int scfsi)
+			      struct channel const *gr0ch, unsigned int scfsi,
+			      unsigned int bits_left, unsigned int *part2_length)
 {
   struct mad_bitptr start;
   unsigned int slen1, slen2, sfbi;
@@ -728,12 +738,20 @@ unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
     sfbi = 0;
 
     nsfb = (channel->flags & mixed_block_flag) ? 8 + 3 * 3 : 6 * 3;
-    while (nsfb--)
+    while (nsfb--) {
+      if (bits_left < slen1)
+	return MAD_ERROR_BADSCFSI;
       channel->scalefac[sfbi++] = mad_bit_read(ptr, slen1);
+      bits_left -= slen1;
+    }
 
     nsfb = 6 * 3;
-    while (nsfb--)
+    while (nsfb--) {
+      if (bits_left < slen2)
+	return MAD_ERROR_BADSCFSI;
       channel->scalefac[sfbi++] = mad_bit_read(ptr, slen2);
+      bits_left -= slen2;
+    }
 
     nsfb = 1 * 3;
     while (nsfb--)
@@ -745,8 +763,12 @@ unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
 	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
     }
     else {
-      for (sfbi = 0; sfbi < 6; ++sfbi)
+      for (sfbi = 0; sfbi < 6; ++sfbi) {
+	if (bits_left < slen1)
+	  return MAD_ERROR_BADSCFSI;
 	channel->scalefac[sfbi] = mad_bit_read(ptr, slen1);
+	bits_left -= slen1;
+      }
     }
 
     if (scfsi & 0x4) {
@@ -754,8 +776,12 @@ unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
 	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
     }
     else {
-      for (sfbi = 6; sfbi < 11; ++sfbi)
+      for (sfbi = 6; sfbi < 11; ++sfbi) {
+	if (bits_left < slen1)
+	  return MAD_ERROR_BADSCFSI;
 	channel->scalefac[sfbi] = mad_bit_read(ptr, slen1);
+	bits_left -= slen1;
+      }
     }
 
     if (scfsi & 0x2) {
@@ -763,8 +789,12 @@ unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
 	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
     }
     else {
-      for (sfbi = 11; sfbi < 16; ++sfbi)
+      for (sfbi = 11; sfbi < 16; ++sfbi) {
+	if (bits_left < slen2)
+	  return MAD_ERROR_BADSCFSI;
 	channel->scalefac[sfbi] = mad_bit_read(ptr, slen2);
+	bits_left -= slen2;
+      }
     }
 
     if (scfsi & 0x1) {
@@ -772,14 +802,19 @@ unsigned int III_scalefactors(struct mad_bitptr *ptr, struct channel *channel,
 	channel->scalefac[sfbi] = gr0ch->scalefac[sfbi];
     }
     else {
-      for (sfbi = 16; sfbi < 21; ++sfbi)
+      for (sfbi = 16; sfbi < 21; ++sfbi) {
+	if (bits_left < slen2)
+	  return MAD_ERROR_BADSCFSI;
 	channel->scalefac[sfbi] = mad_bit_read(ptr, slen2);
+	bits_left -= slen2;
+      }
     }
 
     channel->scalefac[21] = 0;
   }
 
-  return mad_bit_length(&start, ptr);
+  *part2_length = mad_bit_length(&start, ptr);
+  return MAD_ERROR_NONE;
 }
 
 /*
@@ -933,19 +968,17 @@ static
 enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 			      struct channel *channel,
 			      unsigned char const *sfbwidth,
-			      unsigned int part2_length)
+			      signed int part3_length)
 {
   signed int exponents[39], exp;
   signed int const *expptr;
   struct mad_bitptr peek;
-  signed int bits_left, cachesz;
+  signed int bits_left, cachesz, fakebits;
   register mad_fixed_t *xrptr;
   mad_fixed_t const *sfbound;
   register unsigned long bitcache;
 
-  bits_left = (signed) channel->part2_3_length - (signed) part2_length;
-  if (bits_left < 0)
-    return MAD_ERROR_BADPART3LEN;
+  bits_left = part3_length;
 
   III_exponents(channel, sfbwidth, exponents);
 
@@ -956,8 +989,12 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
   cachesz  = mad_bit_bitsleft(&peek);
   cachesz += ((32 - 1 - 24) + (24 - cachesz)) & ~7;
 
+  if (bits_left < cachesz) {
+    cachesz = bits_left;
+  }
   bitcache   = mad_bit_read(&peek, cachesz);
   bits_left -= cachesz;
+  fakebits = 0;
 
   xrptr = &xr[0];
 
@@ -986,7 +1023,7 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 
     big_values = channel->big_values;
 
-    while (big_values-- && cachesz + bits_left > 0) {
+    while (big_values-- && cachesz + bits_left - fakebits > 0) {
       union huffpair const *pair;
       unsigned int clumpsz, value;
       register mad_fixed_t requantized;
@@ -1023,10 +1060,19 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 	unsigned int bits;
 
 	bits       = ((32 - 1 - 21) + (21 - cachesz)) & ~7;
+	if (bits_left < bits) {
+	  bits = bits_left;
+	}
 	bitcache   = (bitcache << bits) | mad_bit_read(&peek, bits);
 	cachesz   += bits;
 	bits_left -= bits;
       }
+      if (cachesz < 21) {
+	unsigned int bits = 21 - cachesz;
+	bitcache <<= bits;
+	cachesz += bits;
+	fakebits += bits;
+      }
 
       /* hcod (0..19) */
 
@@ -1041,6 +1087,8 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
       }
 
       cachesz -= pair->value.hlen;
+      if (cachesz < fakebits)
+	return MAD_ERROR_BADHUFFDATA;
 
       if (linbits) {
 	/* x (0..14) */
@@ -1054,10 +1102,15 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 
 	case 15:
 	  if (cachesz < linbits + 2) {
-	    bitcache   = (bitcache << 16) | mad_bit_read(&peek, 16);
-	    cachesz   += 16;
-	    bits_left -= 16;
+	    unsigned int bits = 16;
+	    if (bits_left < 16)
+	      bits = bits_left;
+	    bitcache   = (bitcache << bits) | mad_bit_read(&peek, bits);
+	    cachesz   += bits;
+	    bits_left -= bits;
 	  }
+	  if (cachesz - fakebits < linbits)
+	    return MAD_ERROR_BADHUFFDATA;
 
 	  value += MASK(bitcache, cachesz, linbits);
 	  cachesz -= linbits;
@@ -1074,6 +1127,8 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 	  }
 
 	x_final:
+	  if (cachesz - fakebits < 1)
+	    return MAD_ERROR_BADHUFFDATA;
 	  xrptr[0] = MASK1BIT(bitcache, cachesz--) ?
 	    -requantized : requantized;
 	}
@@ -1089,10 +1144,15 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 
 	case 15:
 	  if (cachesz < linbits + 1) {
-	    bitcache   = (bitcache << 16) | mad_bit_read(&peek, 16);
-	    cachesz   += 16;
-	    bits_left -= 16;
+	    unsigned int bits = 16;
+	    if (bits_left < 16)
+	      bits = bits_left;
+	    bitcache   = (bitcache << bits) | mad_bit_read(&peek, bits);
+	    cachesz   += bits;
+	    bits_left -= bits;
 	  }
+	  if (cachesz - fakebits < linbits)
+	    return MAD_ERROR_BADHUFFDATA;
 
 	  value += MASK(bitcache, cachesz, linbits);
 	  cachesz -= linbits;
@@ -1109,6 +1169,8 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 	  }
 
 	y_final:
+	  if (cachesz - fakebits < 1)
+	    return MAD_ERROR_BADHUFFDATA;
 	  xrptr[1] = MASK1BIT(bitcache, cachesz--) ?
 	    -requantized : requantized;
 	}
@@ -1128,6 +1190,8 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 	    requantized = reqcache[value] = III_requantize(value, exp);
 	  }
 
+	  if (cachesz - fakebits < 1)
+	    return MAD_ERROR_BADHUFFDATA;
 	  xrptr[0] = MASK1BIT(bitcache, cachesz--) ?
 	    -requantized : requantized;
 	}
@@ -1146,6 +1210,8 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 	    requantized = reqcache[value] = III_requantize(value, exp);
 	  }
 
+	  if (cachesz - fakebits < 1)
+	    return MAD_ERROR_BADHUFFDATA;
 	  xrptr[1] = MASK1BIT(bitcache, cachesz--) ?
 	    -requantized : requantized;
 	}
@@ -1155,9 +1221,6 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
     }
   }
 
-  if (cachesz + bits_left < 0)
-    return MAD_ERROR_BADHUFFDATA;  /* big_values overrun */
-
   /* count1 */
   {
     union huffquad const *table;
@@ -1167,15 +1230,24 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 
     requantized = III_requantize(1, exp);
 
-    while (cachesz + bits_left > 0 && xrptr <= &xr[572]) {
+    while (cachesz + bits_left - fakebits > 0 && xrptr <= &xr[572]) {
       union huffquad const *quad;
 
       /* hcod (1..6) */
 
       if (cachesz < 10) {
-	bitcache   = (bitcache << 16) | mad_bit_read(&peek, 16);
-	cachesz   += 16;
-	bits_left -= 16;
+	unsigned int bits = 16;
+	if (bits_left < 16)
+	  bits = bits_left;
+	bitcache   = (bitcache << bits) | mad_bit_read(&peek, bits);
+	cachesz   += bits;
+	bits_left -= bits;
+      }
+      if (cachesz < 10) {
+	unsigned int bits = 10 - cachesz;
+	bitcache <<= bits;
+	cachesz += bits;
+	fakebits += bits;
       }
 
       quad = &table[MASK(bitcache, cachesz, 4)];
@@ -1188,6 +1260,11 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 		      MASK(bitcache, cachesz, quad->ptr.bits)];
       }
 
+      if (cachesz - fakebits < quad->value.hlen + quad->value.v
+        + quad->value.w + quad->value.x + quad->value.y)
+	/* We don't have enough bits to read one more entry, consider them
+	 * stuffing bits. */
+	break;
       cachesz -= quad->value.hlen;
 
       if (xrptr == sfbound) {
@@ -1236,22 +1313,8 @@ enum mad_error III_huffdecode(struct mad_bitptr *ptr, mad_fixed_t xr[576],
 
       xrptr += 2;
     }
-
-    if (cachesz + bits_left < 0) {
-# if 0 && defined(DEBUG)
-      fprintf(stderr, "huffman count1 overrun (%d bits)\n",
-	      -(cachesz + bits_left));
-# endif
-
-      /* technically the bitstream is misformatted, but apparently
-	 some encoders are just a bit sloppy with stuffing bits */
-
-      xrptr -= 4;
-    }
   }
 
-  assert(-bits_left <= MAD_BUFFER_GUARD * CHAR_BIT);
-
 # if 0 && defined(DEBUG)
   if (bits_left < 0)
     fprintf(stderr, "read %d bits too many\n", -bits_left);
@@ -2348,10 +2411,11 @@ void III_freqinver(mad_fixed_t sample[18][32], unsigned int sb)
  */
 static
 enum mad_error III_decode(struct mad_bitptr *ptr, struct mad_frame *frame,
-			  struct sideinfo *si, unsigned int nch)
+			  struct sideinfo *si, unsigned int nch, unsigned int md_len)
 {
   struct mad_header *header = &frame->header;
   unsigned int sfreqi, ngr, gr;
+  int bits_left = md_len * CHAR_BIT;
 
   {
     unsigned int sfreq;
@@ -2383,6 +2447,7 @@ enum mad_error III_decode(struct mad_bitptr *ptr, struct mad_frame *frame,
     for (ch = 0; ch < nch; ++ch) {
       struct channel *channel = &granule->ch[ch];
       unsigned int part2_length;
+      unsigned int part3_length;
 
       sfbwidth[ch] = sfbwidth_table[sfreqi].l;
       if (channel->block_type == 2) {
@@ -2391,18 +2456,30 @@ enum mad_error III_decode(struct mad_bitptr *ptr, struct mad_frame *frame,
       }
 
       if (header->flags & MAD_FLAG_LSF_EXT) {
-	part2_length = III_scalefactors_lsf(ptr, channel,
+	error = III_scalefactors_lsf(ptr, channel,
 					    ch == 0 ? 0 : &si->gr[1].ch[1],
-					    header->mode_extension);
+					    header->mode_extension, bits_left, &part2_length);
       }
       else {
-	part2_length = III_scalefactors(ptr, channel, &si->gr[0].ch[ch],
-					gr == 0 ? 0 : si->scfsi[ch]);
+	error = III_scalefactors(ptr, channel, &si->gr[0].ch[ch],
+					gr == 0 ? 0 : si->scfsi[ch], bits_left, &part2_length);
       }
+      if (error)
+        return error;
 
-      error = III_huffdecode(ptr, xr[ch], channel, sfbwidth[ch], part2_length);
+      bits_left -= part2_length;
+
+      if (part2_length > channel->part2_3_length)
+        return MAD_ERROR_BADPART3LEN;
+
+      part3_length = channel->part2_3_length - part2_length;
+      if (part3_length > bits_left)
+        return MAD_ERROR_BADPART3LEN;
+
+      error = III_huffdecode(ptr, xr[ch], channel, sfbwidth[ch], part3_length);
       if (error)
 	return error;
+      bits_left -= part3_length;
     }
 
     /* joint stereo processing */
@@ -2519,11 +2596,13 @@ int mad_layer_III(struct mad_stream *stream, struct mad_frame *frame)
   unsigned int nch, priv_bitlen, next_md_begin = 0;
   unsigned int si_len, data_bitlen, md_len;
   unsigned int frame_space, frame_used, frame_free;
-  struct mad_bitptr ptr;
+  struct mad_bitptr ptr, bufend_ptr;
   struct sideinfo si;
   enum mad_error error;
   int result = 0;
 
+  mad_bit_init(&bufend_ptr, stream->bufend);
+
   /* allocate Layer III dynamic structures */
 
   if (stream->main_data == 0) {
@@ -2587,14 +2666,15 @@ int mad_layer_III(struct mad_stream *stream, struct mad_frame *frame)
     unsigned long header;
 
     mad_bit_init(&peek, stream->next_frame);
+    if (mad_bit_length(&peek, &bufend_ptr) >= 57) {
+      header = mad_bit_read(&peek, 32);
+      if ((header & 0xffe60000L) /* syncword | layer */ == 0xffe20000L) {
+        if (!(header & 0x00010000L))  /* protection_bit */
+	  mad_bit_skip(&peek, 16);  /* crc_check */
 
-    header = mad_bit_read(&peek, 32);
-    if ((header & 0xffe60000L) /* syncword | layer */ == 0xffe20000L) {
-      if (!(header & 0x00010000L))  /* protection_bit */
-	mad_bit_skip(&peek, 16);  /* crc_check */
-
-      next_md_begin =
-	mad_bit_read(&peek, (header & 0x00080000L) /* ID */ ? 9 : 8);
+        next_md_begin =
+	  mad_bit_read(&peek, (header & 0x00080000L) /* ID */ ? 9 : 8);
+      }
     }
 
     mad_bit_finish(&peek);
@@ -2653,7 +2733,7 @@ int mad_layer_III(struct mad_stream *stream, struct mad_frame *frame)
   /* decode main_data */
 
   if (result == 0) {
-    error = III_decode(&ptr, frame, &si, nch);
+    error = III_decode(&ptr, frame, &si, nch, md_len);
     if (error) {
       stream->error = error;
       result = -1;
