[PATCH] adpcm: fix stack overflow with >4 channels (CVE-2017-15372)

[Mans Rullgard <mans@mansr.com>]

---
 src/adpcm.c | 8 +++++++-
 src/adpcm.h | 3 +++
 src/wav.c   | 5 ++++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/adpcm.c b/src/adpcm.c
index 2e13867e94b0..f64b7d5c2787 100644
--- a/src/adpcm.c
+++ b/src/adpcm.c
@@ -71,6 +71,11 @@ const short lsx_ms_adpcm_i_coef[7][2] = {
                         { 392,-232}
 };
 
+extern void *lsx_ms_adpcm_alloc(unsigned chans)
+{
+        return lsx_malloc(chans * sizeof(MsState_t));
+}
+
 static inline sox_sample_t AdpcmDecode(sox_sample_t c, MsState_t *state,
                                sox_sample_t sample1, sox_sample_t sample2)
 {
@@ -102,6 +107,7 @@ static inline sox_sample_t AdpcmDecode(sox_sample_t c, MsState_t *state,
 
 /* lsx_ms_adpcm_block_expand_i() outputs interleaved samples into one output buffer */
 const char *lsx_ms_adpcm_block_expand_i(
+        void *priv,
         unsigned chans,          /* total channels             */
         int nCoef,
         const short *coef,
@@ -113,7 +119,7 @@ const char *lsx_ms_adpcm_block_expand_i(
   const unsigned char *ip;
   unsigned ch;
   const char *errmsg = NULL;
-  MsState_t state[4];  /* One decompressor state for each channel */
+  MsState_t *state = priv;  /* One decompressor state for each channel */
 
   /* Read the four-byte header for each channel */
   ip = ibuff;
diff --git a/src/adpcm.h b/src/adpcm.h
index af4d6f08117d..db5cc6152196 100644
--- a/src/adpcm.h
+++ b/src/adpcm.h
@@ -29,8 +29,11 @@
 /* default coef sets */
 extern const short lsx_ms_adpcm_i_coef[7][2];
 
+extern void *lsx_ms_adpcm_alloc(unsigned chans);
+
 /* lsx_ms_adpcm_block_expand_i() outputs interleaved samples into one output buffer */
 extern const char *lsx_ms_adpcm_block_expand_i(
+	void *priv,
 	unsigned chans,          /* total channels             */
 	int nCoef,
 	const short *coef,
diff --git a/src/wav.c b/src/wav.c
index fad334cf56e9..066be6d7732d 100644
--- a/src/wav.c
+++ b/src/wav.c
@@ -82,6 +82,7 @@ typedef struct {
     /* following used by *ADPCM wav files */
     unsigned short nCoefs;          /* ADPCM: number of coef sets */
     short         *lsx_ms_adpcm_i_coefs;          /* ADPCM: coef sets           */
+    void          *ms_adpcm_data;   /* Private data of adpcm decoder */
     unsigned char *packet;          /* Temporary buffer for packets */
     short         *samples;         /* interleaved samples buffer */
     short         *samplePtr;       /* Pointer to current sample  */
@@ -175,7 +176,7 @@ static unsigned short  AdpcmReadBlock(sox_format_t * ft)
         }
     }
 
-    errmsg = lsx_ms_adpcm_block_expand_i(ft->signal.channels, wav->nCoefs, wav->lsx_ms_adpcm_i_coefs, wav->packet, wav->samples, samplesThisBlock);
+    errmsg = lsx_ms_adpcm_block_expand_i(wav->ms_adpcm_data, ft->signal.channels, wav->nCoefs, wav->lsx_ms_adpcm_i_coefs, wav->packet, wav->samples, samplesThisBlock);
 
     if (errmsg)
         lsx_warn("%s", errmsg);
@@ -791,6 +792,7 @@ static int startread(sox_format_t * ft)
 
         /* nCoefs, lsx_ms_adpcm_i_coefs used by adpcm.c */
         wav->lsx_ms_adpcm_i_coefs = lsx_malloc(wav->nCoefs * 2 * sizeof(short));
+        wav->ms_adpcm_data = lsx_ms_adpcm_alloc(wChannels);
         {
             int i, errct=0;
             for (i=0; len>=2 && i < 2*wav->nCoefs; i++) {
@@ -1216,6 +1218,7 @@ static int stopread(sox_format_t * ft)
     free(wav->packet);
     free(wav->samples);
     free(wav->lsx_ms_adpcm_i_coefs);
+    free(wav->ms_adpcm_data);
     free(wav->comment);
     wav->comment = NULL;
 
-- 
2.15.0


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