Fix overflow vulnerability in Gerbview

Corrects an unguarded read that could lead to arbitrary code execution
in specifically crafted gerber files.

Fixes https://gitlab.com/kicad/code/kicad/issues/10700

gerbview/excellon_image.h

@@ -195,11 +195,6 @@ private:
      */
     bool readToolInformation( char*& aText );
 
-    int TCodeNumber( char*& aText )
-    {
-        return DCodeNumber( aText );
-    }
-
     /**
      * End a route command started by M15 ot G01, G02 or G03 command.
      */

gerbview/excellon_read_drill_file.cpp

@@ -903,7 +903,7 @@ bool EXCELLON_IMAGE::Select_Tool( char*& text )
     // in tool selection command, if the tool is not defined in list,
     // and the definition is embedded, it will be entered in list
     char * startline = text;    // the tool id starts here.
-    int tool_id = TCodeNumber( text );
+    int tool_id = CodeNumber( text );
 
     // T0 is legal, but is not a selection tool. it is a special command
     if( tool_id >= 0 )

gerbview/gerber_file_image.h

@@ -232,9 +232,12 @@ public:
      */
     VECTOR2I ReadIJCoord( char*& Text );
 
-    // functions to read G commands or D commands:
-    int GCodeNumber( char*& Text );
-    int DCodeNumber( char*& Text );
+    /**
+     * Reads the next number and returns the value
+     * @param aText Pointer to the input string vector
+     * @return
+     */
+    int CodeNumber( char*& aText );
 
     /**
      * Return a pointer to the D_CODE within this GERBER for the given \a aDCODE.

gerbview/readgerb.cpp

@@ -284,13 +284,13 @@ bool GERBER_FILE_IMAGE::LoadGerberFile( const wxString& aFullFileName )
                 break;
 
             case 'G':    /* Line type Gxx : command */
-                G_command = GCodeNumber( text );
+                G_command = CodeNumber( text );
                 Execute_G_Command( text, G_command );
                 break;
 
             case 'D':       /* Line type Dxx : Tool selection (xx > 0) or
                              * command if xx = 0..9 */
-                D_commande = DCodeNumber( text );
+                D_commande = CodeNumber( text );
                 Execute_DCODE_Command( text, D_commande );
                 break;
 

gerbview/rs274d.cpp

@@ -395,47 +395,23 @@ static void fillArcPOLY( GERBER_DRAW_ITEM* aGbrItem, const VECTOR2I& aStart, con
 }
 
 
-int GERBER_FILE_IMAGE::GCodeNumber( char*& Text )
+int GERBER_FILE_IMAGE::CodeNumber( char*& aText )
 {
-    int   ii = 0;
-    char* text;
-    char  line[1024];
+    int retval;
+    char* endptr;
 
-    if( Text == nullptr )
+    errno = 0;
+
+    retval = strtol( aText + 1, &endptr, 10 );
+
+    if( endptr == aText || errno != 0 )
         return 0;
 
-    Text++;
-    text = line;
+    wxCHECK_MSG( retval < std::numeric_limits<int>::max(), 0, _( "Invalid Code Number" ) );
 
-    while( IsNumber( *Text ) )
-    {
-        *(text++) = *(Text++);
-    }
+    aText = endptr;
 
-    *text = 0;
-    ii    = atoi( line );
-    return ii;
-}
-
-
-int GERBER_FILE_IMAGE::DCodeNumber( char*& Text )
-{
-    int   ii = 0;
-    char* text;
-    char  line[1024];
-
-    if( Text == nullptr )
-        return 0;
-
-    Text++;
-    text = line;
-
-    while( IsNumber( *Text ) )
-        *(text++) = *(Text++);
-
-    *text = 0;
-    ii    = atoi( line );
-    return ii;
+    return static_cast<int>( retval );
 }
 
 
@@ -492,7 +468,7 @@ bool GERBER_FILE_IMAGE::Execute_G_Command( char*& text, int G_command )
 
     case GC_SELECT_TOOL:
     {
-        int D_commande = DCodeNumber( text );
+        int D_commande = CodeNumber( text );
 
         if( D_commande < FIRST_DCODE )
             return false;