path is rect track corners

This was triggered by an exploit that started the first
edge well outside the final rectangle, causing the captured
to exceed the correct result.

Ivan observes that we really only want the first and third
corners to compute the bounds, so remove the tracking code
that looks for a valid range of points, and record the
corners instead.

R=robertphillips@google.com
Bug: 824145,skia:7792
Change-Id: If228573d0f05c7158dba8142c144d13834e691ec
Reviewed-on: https://skia-review.googlesource.com/122081
Commit-Queue: Cary Clark <caryclark@skia.org>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Auto-Submit: Cary Clark <caryclark@skia.org>

3 files changed, 80 insertions, 57 deletions

diff --git a/gm/pathfill.cpp b/gm/pathfill.cpp
index 23fd5302ae..2f44503c4e 100644
--- a/gm/pathfill.cpp
+++ b/gm/pathfill.cpp
@@ -588,4 +588,26 @@ DEF_SIMPLE_GM(bug7792, canvas, 800, 800) {
     path.lineTo(150, 75);
     path.close();
     canvas->drawPath(path, p);
+    // from skbug.com/7792#c41
+    canvas->translate(0, 200);
+    path.reset();
+    path.moveTo(75, 75);
+    path.lineTo(150, 75);
+    path.lineTo(150, 150);
+    path.lineTo(140, 150);
+    path.lineTo(140, 75);
+    path.moveTo(75, 75);
+    path.close();
+    canvas->drawPath(path, p);
+    // from skbug.com/7792#c53
+    canvas->translate(0, 200);
+    path.reset();
+    path.moveTo(75, 75);
+    path.lineTo(150, 75);
+    path.lineTo(150, 150);
+    path.lineTo(140, 150);
+    path.lineTo(140, 75);
+    path.moveTo(75, 75);
+    path.close();
+    canvas->drawPath(path, p);
 }
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index 0bfeae1d91..0683c174f1 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -454,16 +454,15 @@ bool SkPath::isRectContour(bool allowPartial, int* currVerb, const SkPoint** pts
     SkPoint lineStart;  // used to construct line from previous point
     const SkPoint* firstPt = nullptr; // first point in the rect (last of first moves)
     const SkPoint* lastPt = nullptr;  // last point in the rect (last of lines or first if closed)
-    const SkPoint* lastCountedPt = nullptr;  // point creating 3rd corner
+    SkPoint firstCorner;
+    SkPoint thirdCorner;
     const SkPoint* pts = *ptsPtr;
     const SkPoint* savePts = nullptr; // used to allow caller to iterate through a pair of rects
     lineStart.set(0, 0);
-    signed char directions[] = {-1, -1, -1, -1};  // -1 to 3; -1 is uninitialized
+    signed char directions[] = {-1, -1, -1, -1, -1};  // -1 to 3; -1 is uninitialized
     bool closedOrMoved = false;
-    bool addedLine = false;
     bool autoClose = false;
     bool insertClose = false;
-    bool accumulatingRect = false;
     int verbCnt = fPathRef->countVerbs();
     while (*currVerb < verbCnt && (!allowPartial || !autoClose)) {
         uint8_t verb = insertClose ? (uint8_t) kClose_Verb : fPathRef->atVerb(*currVerb);
@@ -472,11 +471,7 @@ bool SkPath::isRectContour(bool allowPartial, int* currVerb, const SkPoint** pts
                 savePts = pts;
                 autoClose = true;
                 insertClose = false;
-                accumulatingRect = false;
             case kLine_Verb: {
-                if (accumulatingRect) {
-                    lastCountedPt = pts;
-                }
                 if (kClose_Verb != verb) {
                     lastPt = pts;
                 }
@@ -488,13 +483,12 @@ bool SkPath::isRectContour(bool allowPartial, int* currVerb, const SkPoint** pts
                 if (lineStart == lineEnd) {
                     break; // single point on side OK
                 }
-                addedLine = true;
                 int nextDirection = rect_make_dir(lineDelta.fX, lineDelta.fY); // 0 to 3
                 if (0 == corners) {
                     directions[0] = nextDirection;
-                    lineStart = lineEnd;
                     corners = 1;
                     closedOrMoved = false;
+                    lineStart = lineEnd;
                     break;
                 }
                 if (closedOrMoved) {
@@ -504,28 +498,34 @@ bool SkPath::isRectContour(bool allowPartial, int* currVerb, const SkPoint** pts
                     break; // colinear with first
                 }
                 closedOrMoved = autoClose;
-                lineStart = lineEnd;
                 if (directions[corners - 1] == nextDirection) {
                     if (3 == corners && kLine_Verb == verb) {
-                        lastCountedPt = lastPt;
+                        thirdCorner = lineEnd;
                     }
+                    lineStart = lineEnd;
                     break; // colinear segment
                 }
-                if (corners >= 4) {
-                    return false; // too many direction changes
-                }
                 directions[corners++] = nextDirection;
                 // opposite lines must point in opposite directions; xoring them should equal 2
-                if (3 == corners) {
-                    if ((directions[0] ^ directions[2]) != 2) {
-                        return false;
-                    }
-                    accumulatingRect = false;
-                } else if (4 == corners) {
-                    if ((directions[1] ^ directions[3]) != 2) {
-                        return false;
-                    }
+                switch (corners) {
+                    case 2:
+                        firstCorner = lineStart;
+                        break;
+                    case 3:
+                        if ((directions[0] ^ directions[2]) != 2) {
+                            return false;
+                        }
+                        thirdCorner = lineEnd;
+                        break;
+                    case 4:
+                        if ((directions[1] ^ directions[3]) != 2) {
+                            return false;
+                        }
+                        break;
+                    default:
+                        return false; // too many direction changes
                 }
+                lineStart = lineEnd;
                 break;
             }
             case kQuad_Verb:
@@ -538,15 +538,13 @@ bool SkPath::isRectContour(bool allowPartial, int* currVerb, const SkPoint** pts
                     *currVerb -= 1;  // try move again afterwards
                     goto addMissingClose;
                 }
-                if (!addedLine) {
+                if (!corners) {
                     firstPt = pts;
-                    accumulatingRect = true;
                 } else {
                     closeXY = *firstPt - *lastPt;
                     if (closeXY.fX && closeXY.fY) {
                         return false;   // we're diagonal, abort
                     }
-                    accumulatingRect = false;
                 }
                 lineStart = *pts++;
                 closedOrMoved = true;
@@ -563,40 +561,24 @@ addMissingClose:
     if (corners < 3 || corners > 4) {
         return false;
     }
-    closeXY = *firstPt - *lastPt;
-    // If autoClose, check if close generates diagonal
-    bool result = 4 == corners && (closeXY.isZero() || (autoClose && (!closeXY.fX || !closeXY.fY)));
-    if (!result) {
-        if (closeXY.fX && closeXY.fY) {
-            return false;   // we're diagonal, abort
-        }
-        // check if we are just an incomplete rectangle, in which case we can
-        // return true, but not claim to be closed.
-        // e.g.
-        //    3 sided rectangle
-        //    4 sided but the last edge is not long enough to reach the start
-        //
-        int closeDirection = rect_make_dir(closeXY.fX, closeXY.fY);
-        // make sure the close-segment doesn't double-back on itself
-        if (3 == corners || 2 == (closeDirection ^ directions[1])) {
-            result = true;
-            autoClose = false;  // we are not closed
-        }
-    }
     if (savePts) {
         *ptsPtr = savePts;
     }
-    if (result && rect) {
-        ptrdiff_t count = lastCountedPt - firstPt + 1;
-        rect->set(firstPt, (int) count);
+    // check if close generates diagonal
+    closeXY = *firstPt - *lastPt;
+    if (closeXY.fX && closeXY.fY) {
+        return false;
     }
-    if (result && isClosed) {
+    if (rect) {
+        rect->set(firstCorner, thirdCorner);
+    }
+    if (isClosed) {
         *isClosed = autoClose;
     }
-    if (result && direction) {
+    if (direction) {
         *direction = directions[0] == ((directions[1] + 1) & 3) ? kCW_Direction : kCCW_Direction;
     }
-    return result;
+    return true;
 }
 
 bool SkPath::isRect(SkRect* rect, bool* isClosed, Direction* direction) const {
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index b108b7f1bf..477b02b7c0 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -2033,7 +2033,7 @@ static void test_isRect(skiatest::Reporter* reporter) {
         { c3, SK_ARRAY_COUNT(c3), false, true },
 
         { d1, SK_ARRAY_COUNT(d1), false, false },
-        { d2, SK_ARRAY_COUNT(d2), false, false },
+        { d2, SK_ARRAY_COUNT(d2), false, true },
         { d3, SK_ARRAY_COUNT(d3), false, false },
     };
 
@@ -2055,7 +2055,8 @@ static void test_isRect(skiatest::Reporter* reporter) {
             bool isClosed;
             SkPath::Direction direction;
             SkPathPriv::FirstDirection cheapDirection;
-            expected.set(tests[testIndex].fPoints, tests[testIndex].fPointCount);
+            int pointCount = tests[testIndex].fPointCount - (d2 == tests[testIndex].fPoints);
+            expected.set(tests[testIndex].fPoints, pointCount);
             REPORTER_ASSERT(reporter, SkPathPriv::CheapComputeFirstDirection(path, &cheapDirection));
             REPORTER_ASSERT(reporter, path.isRect(&computed, &isClosed, &direction));
             REPORTER_ASSERT(reporter, expected == computed);
@@ -5020,11 +5021,11 @@ DEF_TEST(Path_isRect, reporter) {
     REPORTER_ASSERT(reporter, !path.isRect(&rect));
     // isolated from skbug.com/7792#c39
     SkPath::Verb verbs39[] = { SkPath::kMove_Verb, SkPath::kLine_Verb, SkPath::kLine_Verb,
-                               SkPath::kLine_Verb  };
+                               SkPath::kLine_Verb };
     SkPoint points39[] = { {150, 75}, {150, 150}, {75, 150}, {75, 100} };
     path = makePath2(points39, verbs39, SK_ARRAY_COUNT(verbs39));
     REPORTER_ASSERT(reporter, !path.isRect(&rect));
-    // from zero_length_paths_aa
+    // isolated from zero_length_paths_aa
     SkPath::Verb verbsAA[] = { SkPath::kMove_Verb, SkPath::kLine_Verb, SkPath::kLine_Verb,
                                SkPath::kLine_Verb, SkPath::kLine_Verb, SkPath::kLine_Verb,
                                SkPath::kLine_Verb, SkPath::kClose_Verb };
@@ -5034,4 +5035,22 @@ DEF_TEST(Path_isRect, reporter) {
     REPORTER_ASSERT(reporter, path.isRect(&rect));
     compare.set(&pointsAA[0], SK_ARRAY_COUNT(pointsAA));
     REPORTER_ASSERT(reporter, rect == compare);
+    // isolated from skbug.com/7792#c41
+    SkPath::Verb verbs41[] = { SkPath::kMove_Verb, SkPath::kLine_Verb, SkPath::kLine_Verb,
+                               SkPath::kLine_Verb, SkPath::kLine_Verb, SkPath::kMove_Verb,
+                               SkPath::kClose_Verb };
+    SkPoint points41[] = { {75, 75}, {150, 75}, {150, 150}, {140, 150}, {140, 75}, {75, 75} };
+    path = makePath2(points41, verbs41, SK_ARRAY_COUNT(verbs41));
+    REPORTER_ASSERT(reporter, path.isRect(&rect));
+    compare.set(&points41[1], 4);
+    REPORTER_ASSERT(reporter, rect == compare);
+    // isolated from skbug.com/7792#c53
+    SkPath::Verb verbs53[] = { SkPath::kMove_Verb, SkPath::kLine_Verb, SkPath::kLine_Verb,
+                               SkPath::kLine_Verb, SkPath::kLine_Verb, SkPath::kMove_Verb,
+                               SkPath::kClose_Verb };
+    SkPoint points53[] = { {75, 75}, {150, 75}, {150, 150}, {140, 150}, {140, 75}, {75, 75} };
+    path = makePath2(points53, verbs53, SK_ARRAY_COUNT(verbs53));
+    REPORTER_ASSERT(reporter, path.isRect(&rect));
+    compare.set(&points53[1], 4);
+    REPORTER_ASSERT(reporter, rect == compare);
 }