xar: NULL pointer dereference in xar_get_path (util.c)

["Agostino Sarubbo" <ago () gentoo org>]

Description:
xar is an easily extensible archive format.

The complete ASan output of the issue:

# xar -t -f $FILE
==5525==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f075cfb35f6 bp 0x7fff705167b0 sp 
0x7fff70515f38 T0)
==5525==The signal is caused by a READ memory access.
==5525==Hint: address points to the zero page.
    #0 0x7f075cfb35f5 in strlen /tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/string/../sysdeps/x86_64/strlen.S:76
    #1 0x45f5ef in __strdup 
/tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/asan_interceptors.cc:562
    #2 0x7f075decebc8 in xar_get_path /var/tmp/portage/app-arch/xar-1.6.1-r1/work/xar-1.6.1/lib/util.c:95:8
    #3 0x523f93 in print_file /var/tmp/portage/app-arch/xar-1.6.1-r1/work/xar-1.6.1/src/xar.c:214:16
    #4 0x513f07 in list /var/tmp/portage/app-arch/xar-1.6.1-r1/work/xar-1.6.1/src/xar.c:1524:4
    #5 0x513f07 in main /var/tmp/portage/app-arch/xar-1.6.1-r1/work/xar-1.6.1/src/xar.c:2666
    #6 0x7f075cf55680 in __libc_start_main 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289
    #7 0x41af38 in _init (/usr/bin/xar+0x41af38)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/string/../sysdeps/x86_64/strlen.S:76 in strlen
==5525==ABORTING
Affected version:
1.6.1

Fixed version:
N/A

Commit fix:
N/A

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

CVE:
CVE-2017-11125

Reproducer:
https://github.com/asarubbo/poc/blob/master/00287-xar-nullptr-xar_get_path

Timeline:
2017-06-17: bug discovered and reported to upstream
2017-06-28: blog post about the issue
2017-07-10: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2017/06/28/xar-null-pointer-dereference-in-xar_get_path-util-c/

--
Agostino Sarubbo
Gentoo Linux Developer