New base function `FT_Matrix_Check' (#54019). * src/base/ftcalc.c (FT_Matrix_Check): New base function to properly reject degenerate font matrices. * include/freetype/internal/ftcalc.h: Updated. * src/cff/cffparse.c (cff_parse_font_matrix), src/cid/cidload.c (cid_parse_font_matrix), src/type1/t1load.c (t1_parse_font_matrix), src/type42/t42parse.c (t42_parse_font_matrix): Use `FT_Matrix_Check'.
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diff --git a/ChangeLog b/ChangeLog
index 06df64e..0234e60 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2018-06-24 Werner Lemberg <wl@gnu.org>
+
+ New base function `FT_Matrix_Check' (#54019).
+
+ * src/base/ftcalc.c (FT_Matrix_Check): New base function to properly
+ reject degenerate font matrices.
+
+ * include/freetype/internal/ftcalc.h: Updated.
+
+ * src/cff/cffparse.c (cff_parse_font_matrix), src/cid/cidload.c
+ (cid_parse_font_matrix), src/type1/t1load.c (t1_parse_font_matrix),
+ src/type42/t42parse.c (t42_parse_font_matrix): Use
+ `FT_Matrix_Check'.
+
2018-06-23 Werner Lemberg <wl@gnu.org>
Fix typo.
diff --git a/include/freetype/internal/ftcalc.h b/include/freetype/internal/ftcalc.h
index a04a3cb..38c6f77 100644
--- a/include/freetype/internal/ftcalc.h
+++ b/include/freetype/internal/ftcalc.h
@@ -293,6 +293,21 @@ FT_BEGIN_HEADER
/*
+ * Check a matrix. If the transformation would lead to extreme shear or
+ * extreme scaling, for example, return 0. If everything is OK, return 1.
+ *
+ * Based on geometric considerations we use the following inequality to
+ * identify a degenerate matrix.
+ *
+ * 50 * abs(xx*yy - xy*yx) < xx^2 + xy^2 + yx^2 + yy^2
+ *
+ * Value 50 is heuristic.
+ */
+ FT_BASE( FT_Bool )
+ FT_Matrix_Check( const FT_Matrix* matrix );
+
+
+ /*
* A variant of FT_Vector_Transform. See comments for
* FT_Matrix_Multiply_Scaled.
*/
diff --git a/src/base/ftcalc.c b/src/base/ftcalc.c
index 6abc4ed..c96d5d2 100644
--- a/src/base/ftcalc.c
+++ b/src/base/ftcalc.c
@@ -747,6 +747,72 @@
/* documentation is in ftcalc.h */
+ FT_BASE_DEF( FT_Bool )
+ FT_Matrix_Check( const FT_Matrix* matrix )
+ {
+ FT_Matrix m;
+ FT_Fixed val[4];
+ FT_Fixed nonzero_minval, maxval;
+ FT_Fixed temp1, temp2;
+ FT_UInt i;
+
+
+ if ( !matrix )
+ return 0;
+
+ val[0] = FT_ABS( matrix->xx );
+ val[1] = FT_ABS( matrix->xy );
+ val[2] = FT_ABS( matrix->yx );
+ val[3] = FT_ABS( matrix->yy );
+
+ /*
+ * To avoid overflow, we ensure that each value is not larger than
+ *
+ * int(sqrt(2^31 / 4)) = 23170 ;
+ *
+ * we also check that no value becomes zero if we have to scale.
+ */
+
+ maxval = 0;
+ nonzero_minval = FT_LONG_MAX;
+
+ for ( i = 0; i < 4; i++ )
+ {
+ if ( val[i] > maxval )
+ maxval = val[i];
+ if ( val[i] && val[i] < nonzero_minval )
+ nonzero_minval = val[i];
+ }
+
+ if ( maxval > 23170 )
+ {
+ FT_Fixed scale = FT_DivFix( maxval, 23170 );
+
+
+ if ( !FT_DivFix( nonzero_minval, scale ) )
+ return 0; /* value range too large */
+
+ m.xx = FT_DivFix( matrix->xx, scale );
+ m.xy = FT_DivFix( matrix->xy, scale );
+ m.yx = FT_DivFix( matrix->yx, scale );
+ m.yy = FT_DivFix( matrix->yy, scale );
+ }
+ else
+ m = *matrix;
+
+ temp1 = FT_ABS( m.xx * m.yy - m.xy * m.yx );
+ temp2 = m.xx * m.xx + m.xy * m.xy + m.yx * m.yx + m.yy * m.yy;
+
+ if ( temp1 == 0 ||
+ temp2 / temp1 > 50 )
+ return 0;
+
+ return 1;
+ }
+
+
+ /* documentation is in ftcalc.h */
+
FT_BASE_DEF( void )
FT_Vector_Transform_Scaled( FT_Vector* vector,
const FT_Matrix* matrix,
diff --git a/src/cff/cffparse.c b/src/cff/cffparse.c
index 41cc1dd..0e5f951 100644
--- a/src/cff/cffparse.c
+++ b/src/cff/cffparse.c
@@ -604,7 +604,6 @@
FT_Vector* offset = &dict->font_offset;
FT_ULong* upm = &dict->units_per_em;
FT_Byte** data = parser->stack;
- FT_Error error = FT_ERR( Stack_Underflow );
if ( parser->top >= parser->stack + 6 )
@@ -616,8 +615,6 @@
int i;
- error = FT_Err_Ok;
-
dict->has_font_matrix = TRUE;
/* We expect a well-formed font matrix, this is, the matrix elements */
@@ -646,22 +643,11 @@
( max_scaling - min_scaling ) < 0 ||
( max_scaling - min_scaling ) > 9 )
{
- /* Return default matrix in case of unlikely values. */
-
FT_TRACE1(( "cff_parse_font_matrix:"
" strange scaling values (minimum %d, maximum %d),\n"
" "
" using default matrix\n", min_scaling, max_scaling ));
-
- matrix->xx = 0x10000L;
- matrix->yx = 0;
- matrix->xy = 0;
- matrix->yy = 0x10000L;
- offset->x = 0;
- offset->y = 0;
- *upm = 1;
-
- goto Exit;
+ goto Unlikely;
}
for ( i = 0; i < 6; i++ )
@@ -708,10 +694,31 @@
(double)matrix->yy / *upm / 65536,
(double)offset->x / *upm / 65536,
(double)offset->y / *upm / 65536 ));
+
+ if ( !FT_Matrix_Check( matrix ) )
+ {
+ FT_TRACE1(( "cff_parse_font_matrix:"
+ " degenerate values, using default matrix\n" ));
+ goto Unlikely;
+ }
+
+ return FT_Err_Ok;
}
+ else
+ return FT_THROW( Stack_Underflow );
- Exit:
- return error;
+ Unlikely:
+ /* Return default matrix in case of unlikely values. */
+
+ matrix->xx = 0x10000L;
+ matrix->yx = 0;
+ matrix->xy = 0;
+ matrix->yy = 0x10000L;
+ offset->x = 0;
+ offset->y = 0;
+ *upm = 1;
+
+ return FT_Err_Ok;
}
diff --git a/src/cid/cidload.c b/src/cid/cidload.c
index dc458e8..8f2a312 100644
--- a/src/cid/cidload.c
+++ b/src/cid/cidload.c
@@ -200,6 +200,13 @@
matrix->xy = temp[2];
matrix->yy = temp[3];
+ if ( !FT_Matrix_Check( matrix ) )
+ {
+ FT_ERROR(( "t1_parse_font_matrix: invalid font matrix\n" ));
+ parser->root.error = FT_THROW( Invalid_File_Format );
+ return FT_THROW( Invalid_File_Format );
+ }
+
/* note that the font offsets are expressed in integer font units */
offset->x = temp[4] >> 16;
offset->y = temp[5] >> 16;
diff --git a/src/type1/t1load.c b/src/type1/t1load.c
index baf4d42..8bcf2ea 100644
--- a/src/type1/t1load.c
+++ b/src/type1/t1load.c
@@ -1286,6 +1286,13 @@
matrix->xy = temp[2];
matrix->yy = temp[3];
+ if ( !FT_Matrix_Check( matrix ) )
+ {
+ FT_ERROR(( "t1_parse_font_matrix: invalid font matrix\n" ));
+ parser->root.error = FT_THROW( Invalid_File_Format );
+ return;
+ }
+
/* note that the offsets must be expressed in integer font units */
offset->x = temp[4] >> 16;
offset->y = temp[5] >> 16;
diff --git a/src/type42/t42parse.c b/src/type42/t42parse.c
index 009121f..edd27a8 100644
--- a/src/type42/t42parse.c
+++ b/src/type42/t42parse.c
@@ -284,6 +284,13 @@
matrix->xy = temp[2];
matrix->yy = temp[3];
+ if ( !FT_Matrix_Check( matrix ) )
+ {
+ FT_ERROR(( "t42_parse_font_matrix: invalid font matrix\n" ));
+ parser->root.error = FT_THROW( Invalid_File_Format );
+ return;
+ }
+
/* note that the offsets must be expressed in integer font units */
offset->x = temp[4] >> 16;
offset->y = temp[5] >> 16;