Fabian Maurer : gdiplus: Prevent infinite loops due to floating point inaccuracy.

[Alexandre Julliard]

Module: wine
Branch: master
Commit: 36c3a51d6abbdba4054e02c2a10b9fd38f8a3d5d
URL:    https://gitlab.winehq.org/wine/wine/-/commit/36c3a51d6abbdba4054e02c2a10b9fd...

Author: Fabian Maurer 
Date:   Mon Jul 24 17:23:44 2023 +0200

gdiplus: Prevent infinite loops due to floating point inaccuracy.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=52492

---

dlls/gdiplus/graphicspath.c       | 12 +++++++-----
 dlls/gdiplus/tests/graphicspath.c | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/dlls/gdiplus/graphicspath.c b/dlls/gdiplus/graphicspath.c
index 06e17d4b98a..545aaa8441e 100644
--- a/dlls/gdiplus/graphicspath.c
+++ b/dlls/gdiplus/graphicspath.c
@@ -183,14 +183,16 @@ static BOOL flatten_bezier(path_list_node_t *start, REAL x2, REAL y2, REAL x3, R
         mp[2].X = (mp[1].X + mp[3].X) / 2.0;
         mp[2].Y = (mp[1].Y + mp[3].Y) / 2.0;

-        /* Is one pair of the new control points equal to the old control points? */
-        if ((x2 == mp[0].X && y2 == mp[0].Y && x3 == mp[1].X && y3 == mp[1].Y) ||
-            (x2 == mp[3].X && y2 == mp[3].Y && x3 == mp[4].X && y3 == mp[4].Y))
-            continue;
-
         pt = end->pt;
         pt_st = start->pt;

+        /* Test for closely spaced points that don't need to be flattened
+         * Also avoids limited-precision errors in flatness check
+         */
+        if((fabs(pt.X - mp[2].X) + fabs(pt.Y - mp[2].Y) +
+            fabs(pt_st.X - mp[2].X) + fabs(pt_st.Y - mp[2].Y) ) <= flatness * 0.5)
+            continue;
+
         /* check flatness as a half of distance between middle point and a linearized path
          * formula for distance point from line for point (x0, y0) and line (x1, y1) (x2, y2)
          * is defined as (area_triangle / distance_start_end):
diff --git a/dlls/gdiplus/tests/graphicspath.c b/dlls/gdiplus/tests/graphicspath.c
index 7cbcb51edfc..558eedc147f 100644
--- a/dlls/gdiplus/tests/graphicspath.c
+++ b/dlls/gdiplus/tests/graphicspath.c
@@ -1253,6 +1253,42 @@ static void test_flatten(void)
     GdipDeletePath(path);
 }

+static void test_flatten2(void)
+{
+    GpStatus status;
+    GpPath *path;
+
+    status = GdipCreatePath(0, &path);
+    expect(Ok, status);
+    status = GdipStartPathFigure(path);
+    expect(Ok, status);
+
+    /* path seen in the wild that caused a stack overflow */
+    status = GdipAddPathArc(path, -136.33, 20.00, 786.00, 786.00, -105.00, 30.00);
+    expect(Ok, status);
+    status = GdipAddPathArc(path, 256.67, 413.00, 0.00, 0.00, -75.00, -30.00);
+    expect(Ok, status);
+    status = GdipClosePathFigure(path);
+    expect(Ok, status);
+
+    status = GdipFlattenPath(path, NULL, 1.0);
+    expect(Ok, status);
+
+    /* path seen in the wild that caused a stack overflow */
+    /* same path but redo with the manual points that caused a crash */
+    status = GdipResetPath(path);
+    expect(Ok, status);
+    status = GdipAddPathBezier(path, 154.950806, 33.391144, 221.586075, 15.536285, 291.747314, 15.536285, 358.382568, 33.391144);
+    expect(Ok, status);
+    status = GdipAddPathBezier(path, 256.666809, 412.999512, 256.666718, 412.999481, 256.666656, 412.999481, 256.666565, 412.999512);
+    expect(Ok, status);
+    status = GdipClosePathFigure(path);
+    expect(Ok, status);
+    status = GdipFlattenPath(path, NULL, 1.0);
+
+    GdipDeletePath(path);
+}
+
 static path_test_t widenline_path[] = {
     {5.0, 5.0,   PathPointTypeStart, 0, 0}, /*0*/
     {50.0, 5.0,  PathPointTypeLine,  0, 0}, /*1*/
@@ -1935,6 +1971,7 @@ START_TEST(graphicspath)
     test_widen_cap();
     test_isvisible();
     test_empty_rect();
+    test_flatten2();

GdiplusShutdown(gdiplusToken);
 }