Fix assertion failure when decoding malform G4 fax image

Fix assertion failure when decoding malform G4 fax image

The position indexes of color elements must be monotonic increasing.
Bail out if the decoded index is less or equal to the previous index.

BUG=pdfium:615
Committed: https://pdfium.googlesource.com/pdfium/+/3a0a808ff546b5633a2384f4ed156b7ced605c90

[kcwu, 2016-10-06 10:47:09]

kcwu@chromium.org changed reviewers:
+ npm@chromium.org

[kcwu, 2016-10-06 11:05:34]

I proposed this fix according to my study of G4 compression spec
https://www.itu.int/rec/T-REC-T.6-198811-I/en . I believed it is correct but I
could be wrong.

Does pdfium have any tests to verify rendering result of fax codec?

[dsinclair, 2016-10-06 13:03:10]

dsinclair@chromium.org changed reviewers:
+ dsinclair@chromium.org

[dsinclair, 2016-10-06 13:03:10]

The CQ bit was checked by dsinclair@chromium.org

[dsinclair, 2016-10-06 13:03:11]

lgtm

[commit-bot: I haz the power, 2016-10-06 13:03:19]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[dsinclair, 2016-10-06 13:03:31]

On 2016/10/06 11:05:34, kcwu wrote:
> I proposed this fix according to my study of G4 compression spec
> https://www.itu.int/rec/T-REC-T.6-198811-I/en . I believed it is correct but I
> could be wrong.
> 
> Does pdfium have any tests to verify rendering result of fax codec?

As far as I know, there are no current tests of the fax codec.

[commit-bot: I haz the power, 2016-10-06 19:29:19]

Description was changed from

==========
Fix assertion failure when decoding malform G4 fax image

The position indexes of color elements must be monotonic increasing.
Bail out if the decoded index is less or equal to the previous index.

BUG=pdfium:615
==========

to

==========
Fix assertion failure when decoding malform G4 fax image

The position indexes of color elements must be monotonic increasing.
Bail out if the decoded index is less or equal to the previous index.

BUG=pdfium:615

Committed:
https://pdfium.googlesource.com/pdfium/+/3a0a808ff546b5633a2384f4ed156b7ced60...
==========

[commit-bot: I haz the power, 2016-10-06 19:29:20]

Committed patchset #1 (id:1) as
https://pdfium.googlesource.com/pdfium/+/3a0a808ff546b5633a2384f4ed156b7ced60...