Improved a bit mod detection checks.

Check the content of the file to validate the extension selection.

 Some checks are light but either the file format does not provide enough
identifier data or too much code would be needed. But it is better than
nothing.

modules/demux/mod.c

@@ -33,6 +33,7 @@
 #include <vlc_plugin.h>
 #include <vlc_demux.h>
 #include <vlc_meta.h>
+#include <assert.h>
 
 #include <libmodplug/modplug.h>
 
@@ -121,13 +122,16 @@ struct demux_sys_t
 static int Demux  ( demux_t *p_demux );
 static int Control( demux_t *p_demux, int i_query, va_list args );
 
+static int Validate( demux_t *p_demux, const char *psz_ext );
+
 static const char *ppsz_mod_ext[] =
 {
     "mod", "s3m", "xm",  "it",  "669", "amf", "ams", "dbm", "dmf", "dsm",
     "far", "mdl", "med", "mtm", "okt", "ptm", "stm", "ult", "umx", "mt2",
-    "psm", NULL
+    "psm", "abc", NULL
 };
 
+
 /* We load the complete file in memory, put a higher bound
  * of 500 Mo (which is really big anyway) */
 #define MOD_MAX_FILE_SIZE (500*1000*1000)
@@ -158,6 +162,11 @@ static int Open( vlc_object_t *p_this )
         }
         if( ppsz_mod_ext[i] == NULL )
             return VLC_EGENERIC;
+        if( Validate( p_demux, ppsz_mod_ext[i] ) )
+        {
+            msg_Warn( p_demux, "MOD validation failed (ext=%s)", ppsz_mod_ext[i]);
+            return VLC_EGENERIC;
+        }
         msg_Dbg( p_demux, "running MOD demuxer (ext=%s)", ppsz_mod_ext[i] );
     }
 
@@ -371,3 +380,136 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
     }
 }
 
+/*****************************************************************************
+ * Validate: try to ensure it is really a mod file.
+ * The tests are not robust enough to replace extension checks in the general
+ * cases.
+ * TODO: maybe it should return a score, which will be used to bypass the
+ * extension checks when high enough.
+ *****************************************************************************/
+static int Validate( demux_t *p_demux, const char *psz_ext )
+{
+    static const struct
+    {
+        int i_offset;
+        const char *psz_marker;
+    } p_marker[] = {
+        {  0, "ziRCONia" },             /* MMCMP files */
+        {  0, "Extended Module" },      /* XM */
+        { 44, "SCRM" },                 /* S3M */
+        {  0, "IMPM" },                 /* IT */
+        {  0, "MThd" },                 /* MID */
+        {  0, "GF1PATCH110" },          /* PAT */
+        { 20, "!SCREAM!" },             /* STM */
+        { 20, "!Scream!" },             /* STM */
+        { 20, "BMOD2STM" },             /* STM */
+        {  0, "MMD0" },                 /* MED */
+        {  0, "MMD1" },                 /* MED */
+        {  0, "MTM" },                  /* MTM */
+        {  0, "DMDL" },                 /* MDL */
+        {  0, "DBM0" },                 /* DBM */
+        {  0, "if" },                   /* 669 */
+        {  0, "JN" },                   /* 669 */
+        {  0, "FAR\xfe" },              /* FAR */
+        {  0, "Extreme" },              /* AMS */
+        {  0, "OKTASONGCMOD" },         /* OKT */
+        { 44, "PTMF" },                 /* PTM */
+        {  0, "MAS_UTrack_V00" },       /* Ult */
+        {  0, "DDMF" },                 /* DMF */
+        {  8, "DSMFSONG" },             /* DSM */
+        {  0, "\xc1\x83\x2a\x9e" },     /* UMX */
+        {  0, "ASYLUM Music Format V1.0" }, /* AMF */
+        {  0, "PSM\xfe" },              /* PSM */
+        {  0, "PSM " },                 /* PSM */
+        {  0, "MT20" },                 /* MT2 */
+
+        { 1080, "M.K." },               /* MOD */
+        { 1080, "M!K!" },
+        { 1080, "M&K!" },
+        { 1080, "N.T." },
+        { 1080, "CD81" },
+        { 1080, "OKTA" },
+        { 1080, "16CN" },
+        { 1080, "32CN" },
+        { 1080, "FLT" },
+        { 1080, "TDZ" },
+        { 1081, "CHN" },
+        { 1082, "CH" },
+
+        {  -1, NULL }
+    };
+
+    const uint8_t *p_peek;
+    const int i_peek = stream_Peek( p_demux->s, &p_peek, 2048 );
+    if( i_peek < 4 )
+        return VLC_EGENERIC;
+
+    for( int i = 0; p_marker[i].i_offset >= 0; i++ )
+    {
+        const char *psz_marker = p_marker[i].psz_marker;
+        const int i_size = strlen( psz_marker );
+        const int i_offset = p_marker[i].i_offset;
+
+        if( i_peek < i_offset + i_size )
+            continue;
+
+        if( !memcmp( &p_peek[i_offset], psz_marker, i_size ) )
+            return VLC_SUCCESS;
+    }
+
+    /* The only two format left untested are ABC and MOD(old version)
+     * ant they are difficult to test :( */
+
+    /* Check for ABC
+     * TODO i_peek = 2048 is too big for such files */
+    if( !strcasecmp( psz_ext, "abc" ) )
+    {
+        bool b_k = false;
+        bool b_tx = false;
+
+        for( int i = 0; i < i_peek-1; i++ )
+        {
+            b_k |= p_peek[i+0] == 'K' && p_peek[i+1] == ':';
+            b_tx |= ( p_peek[i+0] == 'X' || p_peek[i+0] == 'T') && p_peek[i+1] == ':';
+        }
+        if( !b_k || !b_tx )
+            return VLC_EGENERIC;
+        return VLC_SUCCESS;
+    }
+
+    /* Check for MOD */
+    if( !strcasecmp( psz_ext, "mod" ) && i_peek >= 20 + 15 * 30 )
+    {
+        /* Check that the name is correctly null padded */
+        const uint8_t *p = memchr( p_peek, '\0', 20 );
+        if( p )
+        {
+            for( ; p < &p_peek[20]; p++ )
+            {
+                if( *p )
+                    return VLC_EGENERIC;
+            }
+        }
+
+        for( int i = 0; i < 15; i++ )
+        {
+            const uint8_t *p_sample = &p_peek[20 + i*30];
+
+            /* Check correct null padding */
+            const uint8_t *p = memchr( &p_sample[0], '\0', 22 );
+            if( p )
+            {
+                for( ; p < &p_sample[22]; p++ )
+                {
+                    if( *p )
+                        return VLC_EGENERIC;
+                }
+            }
+
+            if( p_sample[25] > 64 ) /* Volume value */
+                return VLC_EGENERIC;
+        }
+        return VLC_SUCCESS;
+    }
+    return VLC_EGENERIC;
+}