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prevent infinite loops where a stream token's length entry references itself. perform brute force scans in case of a faulty xref table #33

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Eliot Jones
2019-06-08 16:44:26 +01:00
parent 21a4ba597e
commit 2b486dccab
1 changed files with 53 additions and 16 deletions
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51
src/UglyToad.PdfPig/Tokenization/Scanner/PdfTokenScanner.cs
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@@ -45,6 +45,8 @@
public IToken CurrentToken { get; private set; }
private IndirectReference? callingObject;
public long CurrentPosition => coreTokenScanner.CurrentPosition;
public PdfTokenScanner(IInputBytes inputBytes, IObjectLocationProvider objectLocationProvider, IFilterProvider filterProvider,
@@ -94,8 +96,7 @@
if (objectNumber == null || generation == null)
{
throw new PdfDocumentFormatException("The obj operator (start object) was not preceded by a 2 numbers." +
$"Instead got: {previousTokens[0]} {previousTokens[1]} obj");
return false;
}
// Read all tokens between obj and endobj.
@@ -115,13 +116,29 @@
if (ReferenceEquals(coreTokenScanner.CurrentToken, OperatorToken.StartStream))
{
var streamIdentifier = new IndirectReference(objectNumber.Long, generation.Int);
// Prevent an infinite loop where a stream's length references the stream or the stream's offset.
var getLengthFromFile = !(callingObject.HasValue && callingObject.Value.Equals(streamIdentifier));
var outerCallingObject = callingObject;
try
{
callingObject = streamIdentifier;
// Read stream: special case.
if (TryReadStream(coreTokenScanner.CurrentTokenStart, out var stream))
if (TryReadStream(coreTokenScanner.CurrentTokenStart, getLengthFromFile, out var stream))
{
readTokens.Clear();
readTokens.Add(stream);
}
}
finally
{
callingObject = outerCallingObject;
}
}
else
{
readTokens.Add(coreTokenScanner.CurrentToken);
@@ -168,14 +185,14 @@
return true;
}
private bool TryReadStream(long startStreamTokenOffset, out StreamToken stream)
private bool TryReadStream(long startStreamTokenOffset, bool getLength, out StreamToken stream)
{
stream = null;
DictionaryToken streamDictionaryToken = GetStreamDictionary();
// Get the expected length from the stream dictionary if present.
long? length = GetStreamLength(streamDictionaryToken);
long? length = getLength ? GetStreamLength(streamDictionaryToken) : default(long?);
// Verify again that we start with "stream"
var hasStartStreamToken = ReadStreamTokenStart(inputBytes, startStreamTokenOffset);
@@ -491,10 +508,30 @@
if (!MoveNext())
{
throw new InvalidOperationException($"Could not parse the object with reference: {reference}.");
throw new PdfDocumentFormatException($"Could not parse the object with reference: {reference}.");
}
return (ObjectToken)CurrentToken;
var found = (ObjectToken)CurrentToken;
if (found.Number.Equals(reference))
{
return found;
}
// Brute force read the entire file
Seek(0);
while (MoveNext())
{
objectLocationProvider.Cache((ObjectToken)CurrentToken);
}
if (!objectLocationProvider.TryGetCached(reference, out objectToken))
{
throw new PdfDocumentFormatException($"Could not locate object with reference: {reference} despite a full document search.");
}
return objectToken;
}
private ObjectToken GetObjectFromStream(IndirectReference reference, long offset)