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[truetype] Reject 'fvar' loading when num_instances is too small.

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* src/truetype/ttgxvar.c (TT_Get_MM_Var): Reject retrieving master when
'fvar' values locally do not match with sanitized values from initialization
at `sfnt_init_face` time.

Reported as

  https://bugs.chromium.org/p/chromium/issues/detail?id=1360295
This commit is contained in:
Dominik Röttsches 2022-09-06 15:57:11 +03:00 committed by Werner Lemberg
parent 91a7fae777
commit 8e68439a6f
1 changed files with 16 additions and 5 deletions
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21
src/truetype/ttgxvar.c
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@ -2207,6 +2207,11 @@
FT_FRAME_END
};
/* `num_instances' holds the number of all named instances including */
/* the default instance, which might be missing in the table of named */
/* instances (in 'fvar'). This value is validated in `sfobjs.c` and */
/* may be reset to 0 if consistency checks fail. */
num_instances = (FT_UInt)face->root.style_flags >> 16;
/* read the font data and set up the internal representation */
/* if not already done */
@ -2231,6 +2236,17 @@
if ( FT_STREAM_READ_FIELDS( fvar_fields, &fvar_head ) )
goto Exit;
/* If `num_instances` is larger, synthetization of the default */
/* instance is required. If `num_instances` is smaller, */
/* however, the value has been reset to 0 in `sfnt_init_face` */
/* (in `sfobjs.c`); in this case we have underallocated `mmvar` */
/* structs. */
if ( num_instances < fvar_head.instanceCount )
{
error = FT_THROW( Invalid_Table );
goto Exit;
}
usePsName = FT_BOOL( fvar_head.instanceSize ==
6 + 4 * fvar_head.axisCount );
@ -2249,11 +2265,6 @@
else
num_axes = face->blend->num_axis;
/* `num_instances' holds the number of all named instances, */
/* including the default instance which might be missing */
/* in fvar's table of named instances */
num_instances = (FT_UInt)face->root.style_flags >> 16;
/* prepare storage area for MM data; this cannot overflow */
/* 32-bit arithmetic because of the size limits used in the */
/* `fvar' table validity check in `sfnt_init_face' */