CVE-2022-31782: Heap overflow in get_charset in ftbench.c (#8) · Issues · FreeType / FreeType Demo Programs · GitLab

Heap overflow in get_charset in ftbench.c

face->num_glyphs can be zero, as a result, first_index and last_index would be -1. Those variables will be used in get_charset function.

   1244
   1245     if ( first_index >= face->num_glyphs )
   1246       first_index = face->num_glyphs - 1;
 ► 1247     if ( last_index >= face->num_glyphs )
   1248       last_index = face->num_glyphs - 1;
   1249     incr_index = last_index > first_index ? 1 : -1;
   1250

In get_charset, variable i would be assigned -1 and this code would access charset->code[-1] resulting out-of-bound access.

#define FOREACH( i )  for ( i = first_index ;                          \
                            ( first_index <= i && i <= last_index ) || \
                            ( first_index >= i && i >= last_index ) ;  \
                            i += incr_index )

void get_charset(){
    ...
    {
      int  j;


      /* no charmap, do an identity mapping */
      FOREACH( j )
        charset->code[i++] = (FT_ULong)j;
    }
    ...

stack trace:

=================================================================
==2736368==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000130 at pc 0x00000050005f bp 0x7fff84c241b0 sp 0x7fff84c241a8
WRITE of size 8 at 0x602000000130 thread T0
    #0 0x50005e in get_charset /targets/struct/freetype/dbg/freetype-demos/src/ftbench.c:820:28
    #1 0x4fcc28 in main /targets/struct/freetype/dbg/freetype-demos/src/ftbench.c:1420:11
    #2 0x7fb18708b0b2 in __libc_start_main /build/glibc-sMfBJT/glibc-2.31/csu/../csu/libc-start.c:308:16
    #3 0x41f6bd in _start (/targets/struct/freetype/dbg/fuzzrun/ftbench+0x41f6bd)

0x602000000131 is located 0 bytes to the right of 1-byte region [0x602000000130,0x602000000131)
allocated by thread T0 here:
    #0 0x4c4987 in calloc /fuzz/fuzzdeps/llvm-project-11.0.0/compiler-rt/lib/asan/asan_malloc_linux.cpp:154:3
    #1 0x4ffc36 in get_charset /targets/struct/freetype/dbg/freetype-demos/src/ftbench.c:787:32
    #2 0x4fcc28 in main /targets/struct/freetype/dbg/freetype-demos/src/ftbench.c:1420:11
    #3 0x7fb18708b0b2 in __libc_start_main /build/glibc-sMfBJT/glibc-2.31/csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: heap-buffer-overflow /targets/struct/freetype/dbg/freetype-demos/src/ftbench.c:820:28 in get_charset
Shadow bytes around the buggy address:
  0x0c047fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff8000: fa fa 04 fa fa fa 00 fa fa fa 00 fa fa fa 00 fa
  0x0c047fff8010: fa fa 00 fa fa fa 00 fa fa fa fd fa fa fa fd fa
=>0x0c047fff8020: fa fa fd fa fa fa[01]fa fa fa fa fa fa fa fa fa
  0x0c047fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 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
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  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
  Shadow gap:              cc
==2736368==ABORTING
[1]    2736368 abort      ./ftbench -c 1

reproduce steps: ftbench -c 1 ./poc

poc.zip