Predator and CL could not provide any possible suspects.
Using the code search for the file, “cpdf_contentparser.cpp” assigning to concern owner from GIT blame.
Suspecting Commit#
https://pdfium.googlesource.com/pdfium.git/+/6eb7939300d1bc7c31afd5086c1b93d4a7628481

@hnakashima  -- Could you please look into this issue, kindly reassign if it has nothing to do with your changes.
Thank You.

It's unrelated to my recent changes, as it reproduces before them. I'm looking for the culprit.

It's one of these:

commit c667eb4e9ceeadc16e25274cfedf6f01a743daac
Author: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Date:   Tue Jul 3 23:32:33 2018 +0000

    Roll src/third_party/pdfium 95b0293a29b2..94f7b75b4d5d (5 commits)
    
    https://pdfium.googlesource.com/pdfium.git/+log/95b0293a29b2..94f7b75b4d5d
    
    
    git log 95b0293a29b2..94f7b75b4d5d --date=short --no-merges --format='%ad %ae %s'
    2018-07-03 tsepez@chromium.org Use unowned ptr to Node from outside XFA node tree.
    2018-07-03 tsepez@chromium.org Use UnownedPtr<> in cxfa_nodeiteratortemplate.h
    2018-07-03 tsepez@chromium.org Use std::vector<float> in CPDF_Function.
    2018-07-03 thestig@chromium.org Remove a parameter from CPDF_SyntaxParser::FindTag().
    2018-07-03 art-snake@yandex-team.ru Avoid duplicate data buffering in CPDF_SyntaxParser::ReadStream().

It's https://pdfium-review.googlesource.com/c/pdfium/+/35930

The following revision refers to this bug:
  https://pdfium.googlesource.com/pdfium/+/dd1083b47c029d2540aceb246bf80f549781f62f

commit dd1083b47c029d2540aceb246bf80f549781f62f
Author: Henrique Nakashima <hnakashima@chromium.org>
Date: Fri Jul 06 17:28:46 2018

Revert "Avoid duplicate data buffering in CPDF_SyntaxParser::ReadStream()."

This reverts commit 77f15f7883638a4ced131d74c053af10a5970ce9.

Reason for revert: Causes  crbug.com/860210 
Bug:  chromium:860210 

Original change's description:
> Avoid duplicate data buffering in CPDF_SyntaxParser::ReadStream().
> 
> Allow sub-streams created from an IFX_SeekableReadStream to provide
> stream data without copying memory.
> The data will only reside in the top-level stream.
> 
> For example:
> For file
> http://www.major-landrover.ru/upload/attachments/f/9/f96aab07dab04ae89c8a509ec1ef2b31.pdf
> (18 Mb)
> 
> The memory usage is reduced by ~13 Mb.
> 
> Change-Id: I2595c014d0fbe1fdd181cc04965cfd7d901c2d88
> Reviewed-on: https://pdfium-review.googlesource.com/35930
> Commit-Queue: Art Snake <art-snake@yandex-team.ru>
> Reviewed-by: dsinclair <dsinclair@chromium.org>

TBR=tsepez@chromium.org,dsinclair@chromium.org,art-snake@yandex-team.ru

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I947fca17052765935a952a4f25ca48f6599c4af9
Reviewed-on: https://pdfium-review.googlesource.com/37210
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>

[modify] https://crrev.com/dd1083b47c029d2540aceb246bf80f549781f62f/core/fpdfapi/parser/cpdf_syntax_parser.cpp
[modify] https://crrev.com/dd1083b47c029d2540aceb246bf80f549781f62f/testing/embedder_test.cpp
[modify] https://crrev.com/dd1083b47c029d2540aceb246bf80f549781f62f/core/fpdfapi/edit/cpdf_flateencoder.cpp
[modify] https://crrev.com/dd1083b47c029d2540aceb246bf80f549781f62f/core/fpdfapi/edit/cpdf_flateencoder.h
[modify] https://crrev.com/dd1083b47c029d2540aceb246bf80f549781f62f/testing/embedder_test.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fa002bec2565988729a58f9d46af7765c9520fec

commit fa002bec2565988729a58f9d46af7765c9520fec
Author: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Date: Fri Jul 06 20:22:12 2018

Roll src/third_party/pdfium e3c4b205572e..05aa09d3ebfd (2 commits)

https://pdfium.googlesource.com/pdfium.git/+log/e3c4b205572e..05aa09d3ebfd


git log e3c4b205572e..05aa09d3ebfd --date=short --no-merges --format='%ad %ae %s'
2018-07-06 hnakashima@chromium.org Make MarkData::mMarks a vector of RetainPtr<CPDF_ContentMarkItem>
2018-07-06 hnakashima@chromium.org Revert "Avoid duplicate data buffering in CPDF_SyntaxParser::ReadStream()."


Created with:
  gclient setdep -r src/third_party/pdfium@05aa09d3ebfd

The AutoRoll server is located here: https://pdfium-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.



BUG= chromium:860210 
TBR=dsinclair@chromium.org

Change-Id: I3725cb13c5fee7372697f7890495be963ca3d8b3
Reviewed-on: https://chromium-review.googlesource.com/1128102
Reviewed-by: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#573056}
[modify] https://crrev.com/fa002bec2565988729a58f9d46af7765c9520fec/DEPS

ClusterFuzz has detected this issue as fixed in range 573054:573057.

Detailed report: https://clusterfuzz.com/testcase?key=6174059398955008

Fuzzer: ifratric_pdf_generic
Job Type: linux_msan_pdfium
Platform Id: linux

Crash Type: Null-dereference READ
Crash Address: 0x000000000000
Crash State:
  CPDF_StreamParser::ParseNextElement
  CPDF_StreamContentParser::Parse
  CPDF_ContentParser::Parse
  
Sanitizer: memory (MSAN)

Fixed: https://clusterfuzz.com/revisions?job=linux_msan_pdfium&range=573054:573057

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6174059398955008

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 6174059398955008 is verified as fixed, so closing issue as verified.

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

The following revision refers to this bug:
  https://pdfium.googlesource.com/pdfium/+/7c694a4632dc3b11e26d66a44e598a211913d02a

commit 7c694a4632dc3b11e26d66a44e598a211913d02a
Author: Artem Strygin <art-snake@yandex-team.ru>
Date: Wed Jul 11 16:25:14 2018

Fix crash and memory leak.

Do not return size within CPDF_StreamAcc in case when read
data failed.
Also free buffers in this case.

Bug:  chromium:860210 
Change-Id: Ifb2a061d7c8427409b68c33f213c5c55343fb946
Reviewed-on: https://pdfium-review.googlesource.com/37310
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: Art Snake <art-snake@yandex-team.ru>

[modify] https://crrev.com/7c694a4632dc3b11e26d66a44e598a211913d02a/BUILD.gn
[add] https://crrev.com/7c694a4632dc3b11e26d66a44e598a211913d02a/core/fpdfapi/parser/cpdf_stream_acc_unittest.cpp
[modify] https://crrev.com/7c694a4632dc3b11e26d66a44e598a211913d02a/core/fpdfapi/parser/cpdf_stream_acc.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9717e66b37a4336e55a1e420bb998ec4f4e07553

commit 9717e66b37a4336e55a1e420bb998ec4f4e07553
Author: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Date: Wed Jul 11 20:18:32 2018

Roll src/third_party/pdfium e7e454da8e38..b165ffb64e59 (2 commits)

https://pdfium.googlesource.com/pdfium.git/+log/e7e454da8e38..b165ffb64e59


git log e7e454da8e38..b165ffb64e59 --date=short --no-merges --format='%ad %ae %s'
2018-07-11 thestig@chromium.org Use JSGetObject() in more places.
2018-07-11 art-snake@yandex-team.ru Fix crash and memory leak.


Created with:
  gclient setdep -r src/third_party/pdfium@b165ffb64e59

The AutoRoll server is located here: https://pdfium-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.



BUG= chromium:860210 
TBR=dsinclair@chromium.org

Change-Id: I22163f80735fd7ab47b3879c5ebccd91b216a9e0
Reviewed-on: https://chromium-review.googlesource.com/1133860
Reviewed-by: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#574305}
[modify] https://crrev.com/9717e66b37a4336e55a1e420bb998ec4f4e07553/DEPS