lrzip: NULL pointer dereference in bufRead::get (libzpaq.h)

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

Description:
lrzip is a compression utility that excels at compressing large files.

The complete ASan output of the issue:

# lrzip -t $FILE
==24966==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x0000005e7caa bp 0x7f7c755a58d0 sp 
0x7f7c755a5870 T2)    
==24966==The signal is caused by a READ memory access. 
==24966==Hint: address points to the zero page.   
    #0 0x5e7ca9 in bufRead::get() /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.h:485:24 
    #1 0x5856f1 in libzpaq::Decompresser::findBlock(double*) 
/tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.cpp:1236:21 
    #2 0x55f79a in libzpaq::decompress(libzpaq::Reader*, libzpaq::Writer*) 
/tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.cpp:1363:12  
    #3 0x55f4e2 in zpaq_decompress /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.h:538:2 
    #4 0x54b3a4 in zpaq_decompress_buf /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/stream.c:453:2 
    #5 0x54b3a4 in ucompthread /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/stream.c:1534
    #6 0x7f81b7a434a3 in start_thread /tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/nptl/pthread_create.c:333
    #7 0x7f81b6d6e66c in clone 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:109

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.h:485:24 in 
bufRead::get()
Thread T2 created by T0 here:
    #0 0x42d49d in pthread_create 
/tmp/portage/sys-devel/llvm-3.9.1-r1/work/llvm-3.9.1.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:245
    #1 0x53e70f in create_pthread /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/stream.c:133:6
    #2 0x53e70f in fill_buffer /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/stream.c:1673
    #3 0x53e70f in read_stream /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/stream.c:1755
    #4 0x531075 in unzip_literal /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:162:16
    #5 0x531075 in runzip_chunk /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:320
    #6 0x531075 in runzip_fd /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:382
    #7 0x519b41 in decompress_file /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/lrzip.c:826:6
    #8 0x511074 in main /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/main.c:669:4
    #9 0x7f81b6ca778f in __libc_start_main 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289

==24966==ABORTING

Affected version:
0.631

Fixed version:
N/A

Commit fix:
N/A

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

CVE:
CVE-2017-8847

Reproducer:
https://github.com/asarubbo/poc/blob/master/00229-lrzip-nullptr-bufRead-get

Timeline:
2017-03-24: bug discovered and reported to upstream
2017-05-07: blog post about the issue
2017-05-08: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2017/05/07/lrzip-null-pointer-dereference-in-bufreadget-libzpaq-h/

--
Agostino Sarubbo
Gentoo Linux Developer