[PATCH 4/5] usp10: Range check glyph counts in GPOS_apply_ChainContextPos().

[Aric Stewart]

Signed-off-by: Aric Stewart <aric at codeweavers.com>

On 4/5/17 3:21 AM, Henri Verbeet wrote:
> I.e., avoid accessing outside the "glyphs" array. If we're particularly
> unlucky we may actually get a match against data outside the array.
> 
> Signed-off-by: Henri Verbeet <hverbeet at codeweavers.com>
> ---
>  dlls/usp10/opentype.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/dlls/usp10/opentype.c b/dlls/usp10/opentype.c
> index b5ee5d1..9c1d596 100644
> --- a/dlls/usp10/opentype.c
> +++ b/dlls/usp10/opentype.c
> @@ -2235,10 +2235,22 @@ static unsigned int GPOS_apply_ChainContextPos(const ScriptCache *script_cache,
>              TRACE("  subtype 3 (Coverage-based Chaining Context Glyph Positioning)\n");
>  
>              backtrack_count = GET_BE_WORD(backtrack->BacktrackGlyphCount);
> +            k = glyph_index + dirBacktrack * backtrack_count;
> +            if (k < 0 || k >= glyph_count)
> +                continue;
> +
>              input = (const GPOS_ChainContextPosFormat3_2 *)&backtrack->Coverage[backtrack_count];
>              input_count = GET_BE_WORD(input->InputGlyphCount);
> +            k = glyph_index + write_dir * (input_count - 1);
> +            if (k < 0 || k >= glyph_count)
> +                continue;
> +
>              lookahead = (const GPOS_ChainContextPosFormat3_3 *)&input->Coverage[input_count];
>              lookahead_count = GET_BE_WORD(lookahead->LookaheadGlyphCount);
> +            k = glyph_index + dirLookahead * (input_count + lookahead_count - 1);
> +            if (k < 0 || k >= glyph_count)
> +                continue;
> +
>              positioning = (const GPOS_ChainContextPosFormat3_4 *)&lookahead->Coverage[lookahead_count];
>  
>              for (k = 0; k < backtrack_count; ++k)
>