bugThe FreeType Project - Bugs: bug #43548, FreeType 2.5.3 PCF parsing NULL...


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bug #43548: FreeType 2.5.3 PCF parsing NULL pointer dereference due to 32-bit integer overflow

Submitter:  Mateusz Jurczyk <j00ru>
Submitted:  Thu 06 Nov 2014 01:13:57 PM UTC
Severity:  3 - Normal Item Group:  Crash
Status:  Fixed Privacy:  Public
Assigned to:  wl Open/Closed:  Closed
Planned Release:  2.5.4

Thu 06 Nov 2014 10:26:56 PM UTC, comment #1: 

Fixed in git, thanks.

Werner LEMBERG <wl>
Group administrator
Thu 06 Nov 2014 01:13:57 PM UTC, original submission:  

In freetype/src/pcf/pcfread.c, the following code is found:

    int           firstCol, lastCol;
    int           firstRow, lastRow;
    int           nencoding, encodingOffset;
    int           i, j, k;
      firstCol          = FT_GET_SHORT();
      lastCol           = FT_GET_SHORT();
      firstRow          = FT_GET_SHORT();
      lastRow           = FT_GET_SHORT();
      face->defaultChar = FT_GET_SHORT();
    nencoding = ( lastCol - firstCol + 1 ) * ( lastRow - firstRow + 1 );

    if ( FT_NEW_ARRAY( encoding, nencoding ) )
      return FT_THROW( Out_Of_Memory );
    for ( i = firstRow; i <= lastRow; i++ )
      for ( j = firstCol; j <= lastCol; j++ )
        // Load data into the "encoding" array.

Since the "firstCol", "lastCol", "firstRow", "lastRow" variables are all controlled from the input file, if we set them respectively to:

firstCol = -32768
lastCol = 32767
firstRow = -32768
lastRow = 32767

Then the 32-bit variable will overflow as a result of a "65536 * 65536" multiplication, and will become 0. This will lead to the allocator initializing the "encoding" pointer with NULL; the pointer will later be used to write data to, resulting in a NULL pointer dereference and an application crash:

==1143== ERROR: AddressSanitizer: SEGV on unknown address 0x00000000 (pc 0xf6091fe9 sp 0xff819ab0 bp 0xff819bf8 T0)
AddressSanitizer can not provide additional info.
    #0 0xf6091fe8 in pcf_get_encodings freetype2/src/pcf/pcfread.c:841
    #1 0xf6093a49 in pcf_load_font freetype2/src/pcf/pcfread.c:1134
    #2 0xf6095826 in PCF_Face_Init freetype2/src/pcf/pcfdrivr.c:274
    #3 0xf5f9f1d7 in open_face freetype2/src/base/ftobjs.c:1191
    #4 0xf5fa27ea in FT_Open_Face freetype2/src/base/ftobjs.c:2123
    #5 0xf5f9f4ff in FT_New_Face freetype2/src/base/ftobjs.c:1254
    #6 0x804b5a8 in get_face ft2demos-2.5.3/src/ftbench.c:705
    #7 0x804bc64 in main ft2demos-2.5.3/src/ftbench.c:924
SUMMARY: AddressSanitizer: SEGV freetype2/src/pcf/pcfread.c:841 pcf_get_encodings
==1143== ABORTING

The attached "poc.pcf" sample can be used to reproduce the behavior.

Mateusz Jurczyk <j00ru>
Group Member


(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attached Files
file #32379:  poc.pcf added by j00ru (9KiB - application/octet-stream)


Depends on the following items: None found

Items that depend on this one: None found


Carbon-Copy List
  • -email is unavailable- added by wl (Posted a comment)
  • -email is unavailable- added by j00ru (Submitted the item)

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    Follow 6 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2014-11-06 wl StatusNone Fixed
        PrivacyPrivate Public
        Assigned toNone wl
        Open/ClosedOpen Closed
        Planned ReleaseNone 2.5.4
    2014-11-06 j00ru Attached File- Added poc.pcf, #32379

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