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mity / md4c

C Markdown parser. Fast. SAX-like interface. Compliant to CommonMark specification.
MIT License
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Heap buffer overflow in md_merge_lines() #39

Closed ChijinZ closed 6 years ago

ChijinZ commented 6 years ago

command: ./md2html testfile

testcase: https://github.com/ChijinZ/security_advisories/blob/master/md4c-387bd02/crash_md_merge_lines

AddressSanitizer provided information as below:

=================================================================
==21464==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6040000000b1 at pc 0x00000054ff84 bp 0x7fff500be8d0 sp 0x7fff500be8c8
WRITE of size 1 at 0x6040000000b1 thread T0
    #0 0x54ff83 in md_merge_lines /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:878:18
    #1 0x54ff83 in md_merge_lines_alloc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:910
    #2 0x54ff83 in md_is_link_reference_definition_helper /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2154
    #3 0x532108 in md_is_link_reference_definition /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2215:15
    #4 0x532108 in md_consume_link_reference_definitions /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4648
    #5 0x532108 in md_end_current_block /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4694
    #6 0x52c7f7 in md_process_doc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5850:5
    #7 0x5202cb in md_parse /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5917:11
    #8 0x51a7a8 in md_render_html /home/ubuntu/fuzz/test/md4c/md2html/render_html.c:488:12
    #9 0x5195cc in process_file /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:139:11
    #10 0x5195cc in main /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:343
    #11 0x7fda7443a82f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291
    #12 0x41a668 in _start (/home/ubuntu/fuzz/test/md4c/build/md2html/md2html+0x41a668)

0x6040000000b1 is located 0 bytes to the right of 33-byte region [0x604000000090,0x6040000000b1)
allocated by thread T0 here:
    #0 0x4de898 in __interceptor_malloc /home/ubuntu/llvm/llvm-6.0.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:88
    #1 0x54e91f in md_merge_lines_alloc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:904:22
    #2 0x54e91f in md_is_link_reference_definition_helper /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2154
    #3 0x532108 in md_is_link_reference_definition /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2215:15
    #4 0x532108 in md_consume_link_reference_definitions /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4648
    #5 0x532108 in md_end_current_block /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4694

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:878:18 in md_merge_lines
Shadow bytes around the buggy address:
0x0c087fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff8000: fa fa fd fd fd fd fd fd fa fa 00 00 00 00 00 04
=>0x0c087fff8010: fa fa 00 00 00 00[01]fa fa fa fa fa fa fa fa fa
0x0c087fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8060: 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
==21464==ABORTING
mity commented 6 years ago

Minimized the test case into

[\\]: x
mity commented 6 years ago

Fixed.

Thanks for reporting it.