zziplib: invalid memory read in zzip_mem_entry_extra_block (memdisk.c)

Description:
zziplib is an intentionally lightweight library that offers the ability to easily extract data from files archived in a single zip file.

A fuzz on it discovered an invalid memory read.

The complete ASan output:

# unzzipcat-mem $FILE
==7950==ERROR: AddressSanitizer: SEGV on unknown address 0x603000014e32 (pc 0x7f414b4c8693 bp 0x7fff48f3ff70 sp 0x7fff48f3fe40 T0)
==7950==The signal is caused by a READ memory access.
    #0 0x7f414b4c8692 in zzip_mem_entry_extra_block /tmp/portage/dev-libs/zziplib-0.13.62-r1/work/zziplib-0.13.62/zzip/memdisk.c:248:20
    #1 0x7f414b4c8692 in zzip_mem_entry_new /tmp/portage/dev-libs/zziplib-0.13.62-r1/work/zziplib-0.13.62/zzip/memdisk.c:218
    #2 0x7f414b4c8692 in zzip_mem_disk_load /tmp/portage/dev-libs/zziplib-0.13.62-r1/work/zziplib-0.13.62/zzip/memdisk.c:137
    #3 0x7f414b4c78b7 in zzip_mem_disk_open /tmp/portage/dev-libs/zziplib-0.13.62-r1/work/zziplib-0.13.62/zzip/memdisk.c:89:5
    #4 0x50982d in main /tmp/portage/dev-libs/zziplib-0.13.62-r1/work/zziplib-0.13.62/bins/unzzipcat-mem.c:82:12
    #5 0x7f414a60761f in __libc_start_main /var/tmp/portage/sys-libs/glibc-2.22-r4/work/glibc-2.22/csu/libc-start.c:289
    #6 0x419748 in _init (/usr/bin/unzzipcat-mem+0x419748)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /tmp/portage/dev-libs/zziplib-0.13.62-r1/work/zziplib-0.13.62/zzip/memdisk.c:248:20 in zzip_mem_entry_extra_block
==7950==ABORTING

Affected version:
0.13.62

Fixed version:
N/A

Commit fix:
N/A

Credit:
This bug was discovered by Agostino Sarubbo of Gentoo.

CVE:
CVE-2017-5977

Reproducer:
https://github.com/asarubbo/poc/blob/master/00153-zziplib-invalidread-zzip_mem_entry_extra_block

Timeline:
2017-01-17: bug discovered and poked upstream
2017-02-09: blog post about the issue
2017-02-13: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2017/02/09/zziplib-invalid-memory-read-in-zzip_mem_entry_extra_block-memdisk-c