[2019-07-29] - Found with American Fuzzy Lop - CVE-2019-14496

Stack-based buffer overflow in the LoaderXM::load() function, in LoaderXM.cpp.

Issue can be reproduced by running:

```
milkytracker test02.xm
```

```
=================================================================
==5561==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff47f9e510 at pc 0x000000a23468 bp 0x7fff47f9e230 sp 0x7fff47f9e228
WRITE of size 4 at 0x7fff47f9e510 thread T0
    #0 0xa23467 in LoaderXM::load(XMFileBase&, XModule*) /home/fcambus/milkytracker/src/milkyplay/LoaderXM.cpp:646:19
    #1 0x95d324 in XModule::loadModule(XMFileBase&, bool) /home/fcambus/milkytracker/src/milkyplay/XModule.cpp:1976:40
    #2 0x95cd03 in XModule::loadModule(char const*, bool) /home/fcambus/milkytracker/src/milkyplay/XModule.cpp:1954:22
    #3 0x5b2849 in ModuleEditor::openSong(char const*, char const*) /home/fcambus/milkytracker/src/tracker/ModuleEditor.cpp:668:27
    #4 0x7a7226 in Tracker::loadTypeFromFile(FileTypes, PPString const&, bool, bool, bool) /home/fcambus/milkytracker/src/tracker/Tracker.cpp:2694:43
    #5 0x79f10f in Tracker::loadGenericFileType(PPString const&) /home/fcambus/milkytracker/src/tracker/Tracker.cpp:2570:11
    #6 0x7978f8 in Tracker::handleEvent(PPObject*, PPEvent*) /home/fcambus/milkytracker/src/tracker/Tracker.cpp:533:3
    #7 0xa8fdc3 in PPScreen::raiseEvent(PPEvent*) /home/fcambus/milkytracker/src/ppui/Screen.cpp:97:17
    #8 0x815967 in RaiseEventSerialized(PPEvent*) /home/fcambus/milkytracker/src/tracker/sdl/SDL_Main.cpp:150:20
    #9 0x81be7b in SendFile(char*) /home/fcambus/milkytracker/src/tracker/sdl/SDL_Main.cpp:872:2
    #10 0x81c91a in main /home/fcambus/milkytracker/src/tracker/sdl/SDL_Main.cpp:974:3
    #11 0x7f51856b0b6a in __libc_start_main /build/glibc-KRRWSm/glibc-2.29/csu/../csu/libc-start.c:308:16
    #12 0x47b5f9 in _start (/home/fcambus/milkytracker/milkytracker+0x47b5f9)

Address 0x7fff47f9e510 is located in stack of thread T0 at offset 720 in frame
    #0 0xa1a9bf in LoaderXM::load(XMFileBase&, XModule*) /home/fcambus/milkytracker/src/milkyplay/LoaderXM.cpp:64

  This frame has 13 object(s):
    [32, 262) 'insData' (line 65)
    [336, 720) 'smpReloc' (line 66) <== Memory access at offset 720 overflows this variable
    [784, 880) 'nbu' (line 67)
    [912, 914) 'numSamples' (line 144)
    [928, 1960) 'venv' (line 175)
    [2096, 3128) 'penv' (line 176)
    [3264, 3294) 'line' (line 265)
    [3328, 3333) 'slot' (line 365)
    [3360, 3389) 'buffer769' (line 481)
    [3424, 4456) 'venv861' (line 538)
    [4592, 5624) 'penv862' (line 539)
    [5760, 5790) 'line1086' (line 631)
    [5824, 5828) 'buffer1564' (line 832)
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/fcambus/milkytracker/src/milkyplay/LoaderXM.cpp:646:19 in LoaderXM::load(XMFileBase&, XModule*)
Shadow bytes around the buggy address:
  0x100068febc50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100068febc60: 00 00 00 00 00 00 00 00 06 f2 f2 f2 f2 f2 f2 f2
  0x100068febc70: f2 f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100068febc80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100068febc90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x100068febca0: 00 00[f2]f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00
  0x100068febcb0: 00 00 00 00 00 00 f2 f2 f2 f2 f8 f2 f8 f8 f8 f8
  0x100068febcc0: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100068febcd0: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100068febce0: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100068febcf0: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==5561==ABORTING
```