[crash] When using -T and provide a lot of '#', a heap-buffer-overflow is occured

[Ruanxingzhi]

When using -T and provide a lot of '#', a heap-buffer-overflow is occured.

This bug affects versions 3.0.0a only.

Reproduce

Run:

./markdown -T -s '#######################################################################################################################################################################################################################################################################################################################################################################################################'

Result:

root@worklab ~/f/d/src (main)# ./markdown -T -s '#########################################################################################################
##########################################################################################################################################################
####################################################################################################################################'
=================================================================
==17576==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61200000046d at pc 0x5607fa139cd9 bp 0x7ffc3e4567f0 sp 0x7ffc3e455fb0
WRITE of size 386 at 0x61200000046d thread T0
    #0 0x5607fa139cd8 in strcpy (/root/fuzz/discount/src/markdown+0xaccd8) (BuildId: afc94b815b20ad8be244845d74b6694ea7bab3d9)
    #1 0x5607fa1c0b6e in uniquename /root/fuzz/discount/src/toc.c:163:5
    #2 0x5607fa1c04a6 in ___mkd_uniquify /root/fuzz/discount/src/toc.c:192:23
    #3 0x5607fa1c03a6 in ___mkd_uniquify /root/fuzz/discount/src/toc.c:190:6
    #4 0x5607fa199c34 in compile_document /root/fuzz/discount/src/markdown.c:1287:2
    #5 0x5607fa198c5a in mkd3_compile /root/fuzz/discount/src/markdown.c:1494:17
    #6 0x5607fa18d84d in main /root/fuzz/discount/src/main.c:369:6
    #7 0x7f6cc94c76c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #8 0x7f6cc94c7784 in __libc_start_main csu/../csu/libc-start.c:360:3
    #9 0x5607fa0b53f0 in _start (/root/fuzz/discount/src/markdown+0x283f0) (BuildId: afc94b815b20ad8be244845d74b6694ea7bab3d9)

0x61200000046d is located 0 bytes after 301-byte region [0x612000000340,0x61200000046d)
allocated by thread T0 here:
    #0 0x5607fa150042 in __interceptor_malloc (/root/fuzz/discount/src/markdown+0xc3042) (BuildId: afc94b815b20ad8be244845d74b6694ea7bab3d9)
    #1 0x5607fa1c0abc in uniquename /root/fuzz/discount/src/toc.c:162:5
    #2 0x5607fa1c04a6 in ___mkd_uniquify /root/fuzz/discount/src/toc.c:192:23
    #3 0x5607fa1c03a6 in ___mkd_uniquify /root/fuzz/discount/src/toc.c:190:6
    #4 0x5607fa199c34 in compile_document /root/fuzz/discount/src/markdown.c:1287:2
    #5 0x5607fa198c5a in mkd3_compile /root/fuzz/discount/src/markdown.c:1494:17
    #6 0x5607fa18d84d in main /root/fuzz/discount/src/main.c:369:6
    #7 0x7f6cc94c76c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16

SUMMARY: AddressSanitizer: heap-buffer-overflow (/root/fuzz/discount/src/markdown+0xaccd8) (BuildId: afc94b815b20ad8be244845d74b6694ea7bab3d9) in strcpy
Shadow bytes around the buggy address:
  0x612000000180: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
  0x612000000200: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x612000000280: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fa fa
  0x612000000300: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x612000000380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x612000000400: 00 00 00 00 00 00 00 00 00 00 00 00 00[05]fa fa
  0x612000000480: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x612000000500: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x612000000580: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x612000000600: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x612000000680: 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
==17576==ABORTING

Reason

In function uniquename(), the label buffer overflows when calling strcpy().

Possible fix

Malloc sufficient memory for label.

[Orc]

That's a good catch, thank you. You found both a bug and a place where I diverged from the (gruber) standard. A patch has been made and mirrored to github if you want to verify it here.

[Ruanxingzhi]

Verified. Thank you for the fix!