[Poppler-bugs] [Bug 103552] New: Out of bounds memory read when loading zero-bytes PDF

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103552

            Bug ID: 103552
           Summary: Out of bounds memory read when loading zero-bytes PDF
           Product: poppler
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: general
          Assignee: poppler-bugs at lists.freedesktop.org
          Reporter: simon-freedesktop at exyr.org

Steps to reproduce:

* Call poppler_document_new_from_data with data = (char*) 0x1 and len = 0

(0x1 is the dummy pointer that Rust uses when not allocating heap memory in a
zero-size vector of bytes Vec<u8>.)

Expected result: 

* A null pointer is returned and an error is set

Actual result:

* Segfault because this method of MemStream:

  int getChar() override
    { return (bufPtr < bufEnd) ? (*bufPtr++ & 0xff) : EOF; }

… dereferences a null pointer. It was entered with bufEnd == 0x1 (as expected)
and bufPtr == 0x0 (incorrect, should be 0x1).


It looks like this MemStream comes from str->makeSubStream() being called with
an incorrect start position of -1 in XRef::readXRef(). This value came from
getStartXRef() which apparently uses it to signal that "startxref" wasn’t
found. But the caller PDFDoc::setup() doesn’t check for that error and uses the
value as a position for the XRef constructor.

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