Fix UBSAN warnings in SkPerlinNoiseShaderImpl

Also update the docs in places.

Bug: oss-fuzz:6138, oss-fuzz:6275, oss-fuzz:6118
Change-Id: Idfef4118dd6e58f8aa528365895f7d7b8ebc50e5
Reviewed-on: https://skia-review.googlesource.com/128300
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>

2 files changed, 11 insertions, 4 deletions

diff --git a/include/effects/SkPerlinNoiseShader.h b/include/effects/SkPerlinNoiseShader.h
index 5bf3847ae3..6b9bcd86d1 100644
--- a/include/effects/SkPerlinNoiseShader.h
+++ b/include/effects/SkPerlinNoiseShader.h
@@ -27,9 +27,9 @@ public:
     /**
      *  This will construct Perlin noise of the given type (Fractal Noise or Turbulence).
      *
-     *  Both base frequencies (X and Y) have a usual range of (0..1).
+     *  Both base frequencies (X and Y) have a usual range of (0..1) and must be non-negative.
      *
-     *  The number of octaves provided should be fairly small, although no limit is enforced.
+     *  The number of octaves provided should be fairly small, with a limit of 255 enforced.
      *  Each octave doubles the frequency, so 10 octaves would produce noise from
      *  baseFrequency * 1, * 2, * 4, ..., * 512, which quickly yields insignificantly small
      *  periods and resembles regular unstructured noise rather than Perlin noise.
diff --git a/src/shaders/SkPerlinNoiseShader.cpp b/src/shaders/SkPerlinNoiseShader.cpp
index 8f6c85a494..4895683527 100644
--- a/src/shaders/SkPerlinNoiseShader.cpp
+++ b/src/shaders/SkPerlinNoiseShader.cpp
@@ -270,7 +270,8 @@ public:
                 SkScalar highFrequencx =
                     SkScalarCeilToScalar(tileWidth * fBaseFrequency.fX) / tileWidth;
                 // BaseFrequency should be non-negative according to the standard.
-                if (fBaseFrequency.fX / lowFrequencx < highFrequencx / fBaseFrequency.fX) {
+                // lowFrequencx can be 0 if fBaseFrequency.fX is very small.
+                if (sk_ieee_float_divide(fBaseFrequency.fX, lowFrequencx) < highFrequencx / fBaseFrequency.fX) {
                     fBaseFrequency.fX = lowFrequencx;
                 } else {
                     fBaseFrequency.fX = highFrequencx;
@@ -281,7 +282,8 @@ public:
                     SkScalarFloorToScalar(tileHeight * fBaseFrequency.fY) / tileHeight;
                 SkScalar highFrequency =
                     SkScalarCeilToScalar(tileHeight * fBaseFrequency.fY) / tileHeight;
-                if (fBaseFrequency.fY / lowFrequency < highFrequency / fBaseFrequency.fY) {
+                // lowFrequency can be 0 if fBaseFrequency.fY is very small.
+                if (sk_ieee_float_divide(fBaseFrequency.fY, lowFrequency) < highFrequency / fBaseFrequency.fY) {
                     fBaseFrequency.fY = lowFrequency;
                 } else {
                     fBaseFrequency.fY = highFrequency;
@@ -419,6 +421,8 @@ SkPerlinNoiseShaderImpl::SkPerlinNoiseShaderImpl(SkPerlinNoiseShaderImpl::Type t
   , fStitchTiles(!fTileSize.isEmpty())
 {
     SkASSERT(numOctaves >= 0 && numOctaves <= kMaxOctaves);
+    SkASSERT(fBaseFrequencyX >= 0);
+    SkASSERT(fBaseFrequencyY >= 0);
 }
 
 sk_sp<SkFlattenable> SkPerlinNoiseShaderImpl::CreateProc(SkReadBuffer& buffer) {
@@ -426,6 +430,9 @@ sk_sp<SkFlattenable> SkPerlinNoiseShaderImpl::CreateProc(SkReadBuffer& buffer) {
 
     SkScalar freqX = buffer.readScalar();
     SkScalar freqY = buffer.readScalar();
+    if (!buffer.validate(freqX >= 0 && freqY >= 0)) {
+        return nullptr;
+    }
 
     int octaves = buffer.read32LE<int>(kMaxOctaves);