Use of uninitialized value in the md_analyze_line() function

[bsdb0y]

Hi,

While fuzzing md4c 0.4.7 with AFL++ and MSAN, I found out that the md_analyze_line() function may use uninitialized memory.

Attaching a reproducer (gzipped so GitHub accepts it): input01.md.gz

Issue can be reproduced by running:

md2html input01.md

==2793660==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x7f021124c622 in md_analyze_line /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:5985:12
    #1 0x7f021122ee27 in md_process_doc /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:6254:9
    #2 0x7f021122dca5 in md_parse /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:6332:11
    #3 0x7f02112fd66b in md_html /home/bsdboy/md/md4c-release-0.4.7/src/md4c-html.c:571:12
    #4 0x4989fb in process_file /home/bsdboy/md/md4c-release-0.4.7/md2html/md2html.c:144:11
    #5 0x4989fb in main /home/bsdboy/md/md4c-release-0.4.7/md2html/md2html.c:368:11
    #6 0x7f0210e580b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
    #7 0x41c29d in _start (/home/bsdboy/md/md4c-release-0.4.7/build/md2html/md2html+0x41c29d)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:5985:12 in md_analyze_line

with memory origin tracking option -fsanitize-memory-track-origins

==2793563==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x7ffb9423f84f in md_analyze_line /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:5985:12
    #1 0x7ffb9421a49b in md_process_doc /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:6254:9
    #2 0x7ffb94218d8f in md_parse /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:6332:11
    #3 0x7ffb9430c7c4 in md_html /home/bsdboy/md/md4c-release-0.4.7/src/md4c-html.c:571:12
    #4 0x49972f in process_file /home/bsdboy/md/md4c-release-0.4.7/md2html/md2html.c:144:11
    #5 0x49972f in main /home/bsdboy/md/md4c-release-0.4.7/md2html/md2html.c:368:11
    #6 0x7ffb93e430b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
    #7 0x41c29d in _start (/home/bsdboy/md/md4c-release-0.4.7/build/md2html/md2html+0x41c29d)

  Uninitialized value was created by a heap allocation
    #0 0x42847d in malloc (/home/bsdboy/md/md4c-release-0.4.7/build/md2html/md2html+0x42847d)
    #1 0x49ab35 in membuf_init /home/bsdboy/md/md4c-release-0.4.7/md2html/md2html.c:69:17

SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/bsdboy/md/md4c-release-0.4.7/src/md4c.c:5985:12 in md_analyze_line

[mity]

Thanks for reporting, should be now fixed.

[carnil]

The issue was apparently assigned CVE-2021-30027.