This is a serious security regression. If you are not able to fix this quickly, please revert the change that introduced it.

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Probably regression from
https://chromium.googlesource.com/chromium/src/+/d09da8ef0ef6295d8a7e56147f22c0c70d4369ff

There is no skia roll, removing skia component.

pdr: Uh oh! This issue still open and hasn't been updated in the last 14 days. This is a serious vulnerability, and we want to ensure that there's progress. Could you please leave an update with the current status and any potential blockers?

If you're not the right owner for this issue, could you please remove yourself as soon as possible or help us find the right one?

If the issue is fixed or you can't reproduce it, please close the bug. If you've started working on a fix, please set the status to Started.

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For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

I manually bisected this down to "Fix rounding of very large and very small LayoutUnits." (https://chromium.googlesource.com/chromium/src/+/a7b04f8fe15406cbf98995da00fc63f73e9fff61) and am working on a fix.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0df57dd968fae7d34c468d4861f629e62a698c26

commit 0df57dd968fae7d34c468d4861f629e62a698c26
Author: Philip Rogers <pdr@chromium.org>
Date: Sun Oct 01 21:35:42 2017

Ensure scrollbar bitmap is fully initialized

PaintedScrollbarLayer::RasterizeScrollbarPart needs to ensure the scrollbar
bitmap is initialized. The approach was susceptible to floating point errors:
  SkRect rect = SkRect::MakeXYWH(x, y, w, h);
  canvas->translate(-rect.x(), -rect.y());
  canvas->drawRect(rect, p);
If x or y is large, a rect of (w, h) may not actually be drawn. See the
following fiddle: https://fiddle.skia.org/c/b31704a2f4e56979f095b6007be74b54.

This patch clears the scrollbar bitmap before scaling and translating. A TODO
has been added to further improve the code by not painting with an offset. A
test has been added that is only useful for the msan fuzzer.

Bug:  764399 
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6364ec9d69924b4947fb8fcdbb3538a663cd0bed
Reviewed-on: https://chromium-review.googlesource.com/687978
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505522}
[modify] https://crrev.com/0df57dd968fae7d34c468d4861f629e62a698c26/cc/layers/painted_scrollbar_layer.cc
[add] https://crrev.com/0df57dd968fae7d34c468d4861f629e62a698c26/third_party/WebKit/LayoutTests/scrollbars/scrollbar-position-crash-expected.txt
[add] https://crrev.com/0df57dd968fae7d34c468d4861f629e62a698c26/third_party/WebKit/LayoutTests/scrollbars/scrollbar-position-crash.html

ClusterFuzz has detected this issue as fixed in range 505521:505522.

Detailed report: https://clusterfuzz.com/testcase?key=5746585047924736

Fuzzer: marty_html_twiddler
Job Type: linux_msan_chrome
Platform Id: linux

Crash Type: Use-of-uninitialized-value
Crash Address: 
Crash State:
  sse41::blit_row_s32a_opaque
  SkARGB32_Shader_Blitter::blitRect
  SkScan::FillIRect
  
Sanitizer: memory (MSAN)

Recommended Security Severity: Medium

Regressed: https://clusterfuzz.com/revisions?job=linux_msan_chrome&range=491035:491089
Fixed: https://clusterfuzz.com/revisions?job=linux_msan_chrome&range=505521:505522

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5746585047924736

See https://github.com/google/clusterfuzz-tools for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 5746585047924736 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.

This bug has been closed for more than 14 weeks. Removing security view restrictions.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot