Hi Mark, Hi List!
Sorry, for beeing offline for almost a week shortly before the release. I
reviewed the patch now and I think it would be good to have this in the
release! With the patch, behaviour should always be more correct than
without. As there were no objections on the list, I decided to commit the
patch.
Still, I would suggest to delay the release for a few days after this patch
was committed. So, instead of releasing on Wednesday, I suggest to create
the release on the weekend so that everyone has a bit more time to test
this change.
Best regards,
Dominik
On Sat, May 28, 2016 at 10:13 AM, Mark Rogers <mark.rog...@powermapper.com>
wrote:
> Hi
>
> I think I’ve got to the root cause of the reported problems in PdfString.
>
> PdfStrings can be in 2 states: valid or invalid:
>
> /** The string is valid if no error in the constructor has occurred.
> * If it is valid it is safe to call all the other member functions.
> * \returns true if this is a valid initialized PdfString
> */
> inline bool IsValid() const;
>
> The default PdfString constructor deliberately constructs an invalid
> string - this is used for things like PdfString::StringNull (which is
> different from an empty string) and is returned by various methods like
> PdfInfo::GetStringFromInfoDict, PdfField::GetFieldName,
> PdfField::GetAlternateName. There are other PdfString constructors that
> also create an invalid string: PdfString( (char*)NULL ) for example.
>
> When IsValid() returns false various undefined behaviours occur if an
> invalid PdfString is used:
>
> - GetLength / GetUnicodeLength / GetCharacterLength return -1 or -2
> - ToUnicode faults accessing a NULL pointer
> - PdfEncoding::ConvertToUnicode - tries to allocate (SIZE_MAX-1)/2 or
> (SIZE_MAX-2)/2 bytes and throws ePdfError_OutOfMemory if GetCharacterLength
> < 0
> - PdfSimpleEncoding::ConvertToUnicode - tries to allocate SIZE_MAX-1 bytes
> and throws ePdfError_OutOfMemory if GetCharacterLength < 0
> - PdfIdentityEncoding::ConvertToEncoding - tries to allocate SIZE_MAX-1
> bytes and throws ePdfError_OutOfMemory if GetCharacterLength < 0
> - PdfDifferenceEncoding::ConvertToUnicode tries to allocate SIZE_MAX-1 or
> SIZE_MAX-2 bytes and throws ePdfError_OutOfMemory if GetCharacterLength < 0
> - PdfDifferenceEncoding::ConvertToEncoding tries to allocate SIZE_MAX-1 or
> SIZE_MAX-2 bytes and throws ePdfError_OutOfMemory if GetCharacterLength < 0
> - PdfString comparison and equality operators may fault or throw
> ePdfError_OutOfMemory if they try to convert the encoding of one of the
> operands
>
> I think the problems happen because none of the PoDoFo code checks
> PdfString::IsValid, apart from PdfString::GetStringUtf8. I would guess the
> same is true of most PoDoFo client code.
>
> The patch makes PdfString methods have document well-defined safe
> behaviour if IsValid() returns false:
>
> - PdfString::GetLength / PdfString::GetUnicodeLength /
> PdfString::GetCharacterLength return 0 (this prevents allocations of
> SIZE_MAX-1 or SIZE_MAX-2)
> - PdfString::ToUnicode returns an invalid string if it’s called on an
> invalid string
> - the < and > operators return false if LHS and/or RHS are invalid
> - the == operator return false if either LHS or RHS are invalid
> - the == operator return true if both LHS and RHS are invalid
>
> The patch is designed to only change behaviour when the current behaviour
> is bad (i.e. access faults or out of memory errors). Where the current
> behaviour is reasonable there are no changes other than documenting the
> behaviour.
>
> Best Regards
> Mark
>
> Mark Rogers - mark.rog...@powermapper.com
> PowerMapper Software Ltd - www.powermapper.com
> Registered in Scotland No 362274 Quartermile 2 Edinburgh EH3 9GL
>
>
>
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