SkGifCodec: intersect frameRect with image size

When clearing due to SkCodecAnimation::RestoreBGColor_DisposalMethod,
intersect the frameRect with the image size to prevent clearing outside
the bounds of the allocated memory.

Add a test image, created by the fuzzer.

BUG=skia:6046

Change-Id: I43676d28f82abf093ef801752f3a9e881580924c
Reviewed-on: https://skia-review.googlesource.com/5860
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>

1 files changed, 14 insertions, 12 deletions

diff --git a/src/codec/SkGifCodec.cpp b/src/codec/SkGifCodec.cpp
index 9a5948b2d0..618a5b5302 100644
--- a/src/codec/SkGifCodec.cpp
+++ b/src/codec/SkGifCodec.cpp
@@ -419,18 +419,20 @@ SkCodec::Result SkGifCodec::decodeFrame(bool firstAttempt, const Options& opts,
             }
             const auto* prevFrame = fReader->frameContext(frameContext->getRequiredFrame());
             if (prevFrame->getDisposalMethod() == SkCodecAnimation::RestoreBGColor_DisposalMethod) {
-                const SkIRect prevRect = prevFrame->frameRect();
-                auto left = get_scaled_dimension(prevRect.fLeft, fSwizzler->sampleX());
-                auto top = get_scaled_dimension(prevRect.fTop, fSwizzler->sampleY());
-                void* const eraseDst = SkTAddOffset<void>(fDst, top * fDstRowBytes
-                        + left * SkColorTypeBytesPerPixel(dstInfo.colorType()));
-                auto width = get_scaled_dimension(prevRect.width(), fSwizzler->sampleX());
-                auto height = get_scaled_dimension(prevRect.height(), fSwizzler->sampleY());
-                // fSwizzler->fill() would fill to the scaled width of the frame, but we want to
-                // fill to the scaled with of the width of the PRIOR frame, so we do all the scaling
-                // ourselves and call the static version.
-                SkSampler::Fill(dstInfo.makeWH(width, height), eraseDst,
-                                fDstRowBytes, this->getFillValue(dstInfo), kNo_ZeroInitialized);
+                SkIRect prevRect = prevFrame->frameRect();
+                if (prevRect.intersect(this->getInfo().bounds())) {
+                    auto left = get_scaled_dimension(prevRect.fLeft, fSwizzler->sampleX());
+                    auto top = get_scaled_dimension(prevRect.fTop, fSwizzler->sampleY());
+                    void* const eraseDst = SkTAddOffset<void>(fDst, top * fDstRowBytes
+                            + left * SkColorTypeBytesPerPixel(dstInfo.colorType()));
+                    auto width = get_scaled_dimension(prevRect.width(), fSwizzler->sampleX());
+                    auto height = get_scaled_dimension(prevRect.height(), fSwizzler->sampleY());
+                    // fSwizzler->fill() would fill to the scaled width of the frame, but we want to
+                    // fill to the scaled with of the width of the PRIOR frame, so we do all the
+                    // scaling ourselves and call the static version.
+                    SkSampler::Fill(dstInfo.makeWH(width, height), eraseDst,
+                                    fDstRowBytes, this->getFillValue(dstInfo), kNo_ZeroInitialized);
+                }
             }
             filledBackground = true;
         }