Michael Klink created PDFBOX-4997:
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Summary: Incremental update adds certain objects not marked as
needing update
Key: PDFBOX-4997
URL: https://issues.apache.org/jira/browse/PDFBOX-4997
Project: PDFBox
Issue Type: Bug
Components: Writing
Affects Versions: 2.0.21, 3.0.0 PDFBox
Reporter: Michael Klink
Attachments: signed-000.pdf
_This bug causes the eSignature DSS issue
[DSS-2260|https://ec.europa.eu/cefdigital/tracker/browse/DSS-2260]._
If during an incremental update an indirect object containing only a name
object is checked for need of writing, it always is added to the objects to
write and, therefore, eventually written to the update section.
For example in the attached document {{signed-000.pdf}} each page has a color
space resource entry *CS1* referring to the indirect object 54 containing only
the name object, *DeviceGray*. Whenever a page is marked as needing an update,
the bug causes object 54 also to be written even if it is not changed at all.
While this seems like a minor annoyance only, it has serious repercussions: In
multi-signature use cases this makes Adobe Reader claim previous signatures to
be broken whenever a new signature with visualization is added using PDFBox,
see also [DSS-2260|https://ec.europa.eu/cefdigital/tracker/browse/DSS-2260].
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The cause of the bug is
{{org.apache.pdfbox.pdfwriter.COSWriter.addObjectToWrite(COSBase)}} where the
following {{if}} clause attempts to determine whether the inspected object does
not need to be written:
{code:java}
if (actual != null && objectKeys.containsKey(actual)
&& object instanceof COSUpdateInfo &&
!((COSUpdateInfo)object).isNeedToBeUpdated()
&& cosBase instanceof COSUpdateInfo &&
!((COSUpdateInfo)cosBase).isNeedToBeUpdated() )
{
return;
}
{code}
Here {{cosBase}} contains the content of the indirect object, in the case in
question the {{COSName}} *DeviceGray*. As {{COSName}} does not implement
{{COSUpdateInfo}}, the condition never evaluates to {{true}}, so the flow never
returns here but instead always continues with the following lines where the
object is added to the collection of objects to write.
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