Heap buffer overflow in OP_SEND

[clayton-shopify]

The following input demonstrates a crash:

def a(n)
  if n >= 0
    instance_exec(0) {}
    a(n-1)
  end
end

a(1000)

ASAN report:

==59006==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62300000dd00 at pc 0x00010a51f2f8 bp 0x7fff55ae2f90 sp 0x7fff55ae2740
READ of size 16 at 0x62300000dd00 thread T0
    #0 0x10a51f2f7 in __asan_memcpy (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x4d2f7)
    #1 0x10a281cc6 in mrb_vm_exec (mruby:x86_64+0x10016ecc6)
    #2 0x10a2762e6 in mrb_vm_run (mruby:x86_64+0x1001632e6)
    #3 0x10a2aae0f in mrb_top_run (mruby:x86_64+0x100197e0f)
    #4 0x10a37d9d5 in mrb_load_exec (mruby:x86_64+0x10026a9d5)
    #5 0x10a37e325 in mrb_load_file_cxt (mruby:x86_64+0x10026b325)
    #6 0x10a1155b6 in main mruby.c:227
    #7 0x7fffe5638234 in start (libdyld.dylib:x86_64+0x5234)

0x62300000dd00 is located 0 bytes to the right of 6144-byte region [0x62300000c500,0x62300000dd00)
allocated by thread T0 here:
    #0 0x10a528520 in wrap_realloc (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x56520)
    #1 0x10a209be5 in mrb_default_allocf (mruby:x86_64+0x1000f6be5)
    #2 0x10a18a958 in mrb_realloc_simple gc.c:203
    #3 0x10a18b0ae in mrb_realloc gc.c:217
    #4 0x10a2ab89f in stack_extend_alloc (mruby:x86_64+0x10019889f)
    #5 0x10a26d42f in stack_extend (mruby:x86_64+0x10015a42f)
    #6 0x10a282b9e in mrb_vm_exec (mruby:x86_64+0x10016fb9e)
    #7 0x10a2762e6 in mrb_vm_run (mruby:x86_64+0x1001632e6)
    #8 0x10a2aae0f in mrb_top_run (mruby:x86_64+0x100197e0f)
    #9 0x10a37d9d5 in mrb_load_exec (mruby:x86_64+0x10026a9d5)
    #10 0x10a37e325 in mrb_load_file_cxt (mruby:x86_64+0x10026b325)
    #11 0x10a1155b6 in main mruby.c:227
    #12 0x7fffe5638234 in start (libdyld.dylib:x86_64+0x5234)

SUMMARY: AddressSanitizer: heap-buffer-overflow (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x4d2f7) in __asan_memcpy
Shadow bytes around the buggy address:
  0x1c4600001b50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c4600001b60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c4600001b70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c4600001b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1c4600001b90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x1c4600001ba0:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c4600001bb0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c4600001bc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c4600001bd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c4600001be0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c4600001bf0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
==59006==ABORTING
Abort trap: 6

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

[clayton-shopify]

It appears this was introduced by c041206.