mupdf: use-after-free in pdf_to_num (pdf-object.c)

Description:
mupdf is a lightweight PDF viewer and toolkit written in portable C.

A fuzzing through mutool revealed a use-after-free.

The complete ASan output:

# mutool info $FILE
==5430==ERROR: AddressSanitizer: heap-use-after-free on address 0x60300000ea42 at pc 0x7fbc4c3824e5 bp 0x7ffee68ead70 sp 0x7ffee68ead68                                                                                                                                       
READ of size 1 at 0x60300000ea42 thread T0                                                                                                                                                                                                                                    
    #0 0x7fbc4c3824e4 in pdf_to_num /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/pdf/pdf-object.c:375:35                                                                                                                                                       
    #1 0x53f042 in gatherfonts /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/pdfinfo.c:259:46                                                                                                                                                             
    #2 0x53f042 in gatherresourceinfo /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/pdfinfo.c:595                                                                                                                                                         
    #3 0x53913a in gatherpageinfo /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/pdfinfo.c:661:2                                                                                                                                                           
    #4 0x53913a in showinfo /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/pdfinfo.c:957                                                                                                                                                                   
    #5 0x537d46 in pdfinfo_info /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/pdfinfo.c:1029:3                                                                                                                                                            
    #6 0x537d46 in pdfinfo_main /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/pdfinfo.c:1077                                                                                                                                                              
    #7 0x4f8ace in main /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/tools/mutool.c:104:12                                                                                                                                                                     
    #8 0x7fbc4ae1f61f in __libc_start_main /var/tmp/portage/sys-libs/glibc-2.22-r4/work/glibc-2.22/csu/libc-start.c:289                                                                                                                                                       
    #9 0x41f9c8 in _init (/usr/bin/mutool+0x41f9c8)                                                                                                                                                                                                                           
                                                                                                                                                                                                                                                                              
0x60300000ea42 is located 2 bytes inside of 24-byte region [0x60300000ea40,0x60300000ea58)                                                                                                                                                                                    
freed by thread T0 here:                                                                                                                                                                                                                                                      
    #0 0x4c6c10 in free /var/tmp/portage/sys-devel/llvm-3.8.0-r3/work/llvm-3.8.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:38                                                                                                                                    
    #1 0x7fbc4bf33830 in fz_free /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/fitz/memory.c:187:2                                                                                                                                                              
                                                                                                                                                                                                                                                                              
previously allocated by thread T0 here:                                                                                                                                                                                                                                       
    #0 0x4c6f18 in malloc /var/tmp/portage/sys-devel/llvm-3.8.0-r3/work/llvm-3.8.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:52                                                                                                                                  
    #1 0x7fbc4bf2a86f in do_scavenging_malloc /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/fitz/memory.c:17:7                                                                                                                                                  
    #2 0x7fbc4bf2a86f in fz_malloc /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/fitz/memory.c:57                                                                                                                                                               
    #3 0x7fbc4c37f94d in pdf_new_indirect /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/pdf/pdf-object.c:186:8                                                                                                                                                  
                                                                                                                                                                                                                                                                              
SUMMARY: AddressSanitizer: heap-use-after-free /var/tmp/portage/app-text/mupdf-1.9a/work/mupdf-1.9a/source/pdf/pdf-object.c:375:35 in pdf_to_num                                                                                                                              
Shadow bytes around the buggy address:                                                                                                                                                                                                                                        
  0x0c067fff9cf0: fd fd fa fa fd fd fd fa fa fa fd fd fd fa fa fa                                                                                                                                                                                                             
  0x0c067fff9d00: fd fd fd fd fa fa fd fd fd fa fa fa fd fd fd fa                                                                                                                                                                                                             
  0x0c067fff9d10: fa fa fd fd fd fd fa fa fd fd fd fa fa fa fd fd                                                                                                                                                                                                             
  0x0c067fff9d20: fd fa fa fa fd fd fd fd fa fa fd fd fd fa fa fa
  0x0c067fff9d30: fd fd fd fa fa fa fd fd fd fa fa fa fd fd fd fa
=>0x0c067fff9d40: fa fa 00 00 00 fa fa fa[fd]fd fd fa fa fa fd fd
  0x0c067fff9d50: fd fd fa fa 00 00 00 fa fa fa 00 00 00 fa fa fa
  0x0c067fff9d60: 00 00 00 fa fa fa 00 00 00 00 fa fa 00 00 00 fa
  0x0c067fff9d70: fa fa 00 00 00 fa fa fa 00 00 00 06 fa fa 00 00
  0x0c067fff9d80: 01 fa fa fa 00 00 05 fa fa fa 00 00 00 fa fa fa
  0x0c067fff9d90: 00 00 00 00 fa fa 00 00 00 00 fa fa 00 00 00 fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==5430==ABORTING

Affected version:
1.9a

Fixed version:
1.10

Commit fix:
http://git.ghostscript.com/?p=mupdf.git;h=1e03c06456d997435019fb3526fa2d4be7dbc6ec

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

CVE:
CVE-2016-8674

Timeline:
2016-08-05: bug discovered
2016-08-05: bug reported privately to upstream
2016-09-22: upstream released a patch
2016-09-22: blog post about the issue
2016-10-16: CVE Assigned
2016-10-21: upstream released 1.10

Note:
This bug was found with American Fuzzy Lop.

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mupdf: use-after-free in pdf_to_num (pdf-object.c)

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