imageworsener: divide-by-zero in iwgif_record_pixel (imagew-gif.c)

[Agostino Sarubbo <ago () gentoo org>]

Description:
imageworsener is a utility for image scaling and processing.

A fuzz on it discovered a divide-by-zero.

The complete ASan output:

# imagew $FILE /tmp/out -outfmt bmp
==20305==ERROR: AddressSanitizer: FPE on unknown address 0x7f8e57340cd6 (pc 
0x7f8e57340cd6 bp 0x7ffc0fee8910 sp 0x7ffc0fee87e0 T0)                                                                  
              
    #0 0x7f8e57340cd5 in iwgif_record_pixel /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:213:13                                                
                           
    #1 0x7f8e57340cd5 in lzw_emit_code /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:312                                                   
                                
    #2 0x7f8e57339a94 in lzw_process_code /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:376:3                                                 
                             
    #3 0x7f8e57339a94 in lzw_process_bytes /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:433                                                   
                            
    #4 0x7f8e57339a94 in iwgif_read_image /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:669                                                   
                             
    #5 0x7f8e57339a94 in iwgif_read_main /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:724                                                   
                              
    #6 0x7f8e5732fb71 in iw_read_gif_file /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:773:6                                                 
                             
    #7 0x7f8e572e9091 in iw_read_file_by_fmt /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-allfmts.c:61:12                                             
                          
    #8 0x519304 in iwcmd_run /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-cmd.c:1191:6                                                
                                          
    #9 0x515326 in iwcmd_main /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-cmd.c:3018:7                                                
                                         
    #10 0x515326 in main /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-cmd.c:3067                                                  
                                              
    #11 0x7f8e562f078f in __libc_start_main /tmp/portage/sys-libs/glibc-2.23-
r3/work/glibc-2.23/csu/../csu/libc-start.c:289                                                                          
             
    #12 0x41b028 in _init (/usr/bin/imagew+0x41b028)                                                                    
                                                                                          
                                                                                                                        
                                                                                          
AddressSanitizer can not provide additional info.                                                                       
                                                                                          
SUMMARY: AddressSanitizer: FPE /tmp/portage/media-
gfx/imageworsener-1.3.0/work/imageworsener-1.3.0/src/imagew-gif.c:213:13 in 
iwgif_record_pixel                                                                  
==20305==ABORTING

Affected version:
1.3.0

Fixed version:
N/A

Commit fix:
https://github.com/jsummers/imageworsener/commit/ca3356eb49fee03e2eaf6b6aff826988c1122d93

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

CVE:
CVE-2017-7962

Reproducer:
https://github.com/asarubbo/poc/blob/master/00270-imageworsener-FPE-iwgif_record_pixel

Timeline:
2017-04-12: bug discovered and reported to upstream
2017-04-14: upstream released a patch
2017-04-17: blog post about the issue
2017-04-19: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2017/04/17/imageworsener-divide-by-zero-in-iwgif_record_pixel-imagew-gif-c/

-- 
Agostino Sarubbo
Gentoo Linux Developer