heap-buffer-overflow in sixel_encode_highcolor at tosixel.c:1338

[SuhwanSong]

version : img2sixel 1.8.2

There is a heap-buffer-overflow in sixel_encode_highcolor at tosixel.c:1338
please run following cmd to reproduce it.

img2sixel --high-color $PoC

poc
ASAN LOG

==29035==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000004e11 at pc 0x7fc22c9f8b05 bp 0x7fffb3bda610 sp 0x7fffb3bda608
READ of size 1 at 0x602000004e11 thread T0
    #0 0x7fc22c9f8b04 in sixel_encode_highcolor /home/tmp/libsixel/src/tosixel.c:1338:25
    #1 0x7fc22c9f8b04 in sixel_encode /home/tmp/libsixel/src/tosixel.c:1485
    #2 0x7fc22cd2c8a4 in sixel_encoder_output_without_macro /home/tmp/libsixel/src/encoder.c:820:14
    #3 0x7fc22cd2c8a4 in sixel_encoder_encode_frame /home/tmp/libsixel/src/encoder.c:1050
    #4 0x7fc22cae2d91 in sixel_helper_load_image_file /home/tmp/libsixel/src/loader.c:913:14
    #5 0x7fc22cd24d4f in sixel_encoder_encode /home/tmp/libsixel/src/encoder.c:1737:14
    #6 0x51787f in main /home/tmp/libsixel/converters/img2sixel.c:457:22
    #7 0x7fc22b087b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
    #8 0x41a379 in _start (/home/tmp/img2sixel+0x41a379)

0x602000004e11 is located 0 bytes to the right of 1-byte region [0x602000004e10,0x602000004e11)
allocated by thread T0 here:
    #0 0x4da230 in __interceptor_malloc (/home/tmp/img2sixel+0x4da230)
    #1 0x7fc22cd2c3ee in sixel_encoder_output_without_macro /home/tmp/libsixel/src/encoder.c:784:26
    #2 0x7fc22cd2c3ee in sixel_encoder_encode_frame /home/tmp/libsixel/src/encoder.c:1050
    #3 0x7fc22cae2d91 in sixel_helper_load_image_file /home/tmp/libsixel/src/loader.c:913:14
    #4 0x7fc22cd24d4f in sixel_encoder_encode /home/tmp/libsixel/src/encoder.c:1737:14
    #5 0x51787f in main /home/tmp/libsixel/converters/img2sixel.c:457:22
    #6 0x7fc22b087b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/tmp/libsixel/src/tosixel.c:1338:25 in sixel_encode_highcolor
Shadow bytes around the buggy address:
  0x0c047fff8970: fa fa fd fd fa fa fd fd fa fa fd fd fa fa fd fd
  0x0c047fff8980: fa fa fd fd fa fa fd fd fa fa fd fd fa fa fd fd
  0x0c047fff8990: fa fa fd fd fa fa fd fd fa fa fd fd fa fa fd fd
  0x0c047fff89a0: fa fa fd fd fa fa fd fd fa fa fd fd fa fa fd fd
  0x0c047fff89b0: fa fa fd fd fa fa fd fd fa fa fd fd fa fa 01 fa
=>0x0c047fff89c0: fa fa[01]fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff89d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff89e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff89f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8a00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8a10: 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
==29035==ABORTING

[saitoha]

It seems to be fixed with #93. Thanks!