lrzip: divide-by-zero 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
Decompressing...
ASAN:DEADLYSIGNAL
=================================================================
==8026==ERROR: AddressSanitizer: FPE on unknown address 0x0000005e7957 (pc 0x0000005e7957 bp 0x7fcdf9ba58d0 sp 
0x7fcdf9ba5870 T1)
    #0 0x5e7956 in bufRead::get() /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.h:468:41
    #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 0x7fd33c0594a3 in start_thread /tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/nptl/pthread_create.c:333
    #7 0x7fd33b38466c 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: FPE /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/libzpaq/libzpaq.h:468:41 in 
bufRead::get() 
Thread T1 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 0x5303e3 in read_u8 /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:55:6    
    #5 0x5303e3 in read_header /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:144 
    #6 0x5303e3 in runzip_chunk /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:314
    #7 0x5303e3 in runzip_fd /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/runzip.c:382   
    #8 0x519b41 in decompress_file /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/lrzip.c:826:6 
    #9 0x511074 in main /tmp/portage/app-arch/lrzip-0.631/work/lrzip-0.631/main.c:669:4   
    #10 0x7fd33b2bd78f in __libc_start_main 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289  

==8026==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-2017-8842

Reproducer:
https://github.com/asarubbo/poc/blob/master/00228-lrzip-fpe-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:
http://blogs.gentoo.org/ago/2017/05/07/lrzip-divide-by-zero-in-bufreadget-libzpaq-h/

--
Agostino Sarubbo
Gentoo Linux Developer