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Commitb152cb4

Browse files
Improve directory entry validation
Although EndOfChain is not technically valid for directory entry startIDs accoring to the CFB spec, it does appear to be used in practice bythe Microsoft Structured Storage implementation.Fixes:#294
1 parent055a044 commitb152cb4

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6 files changed

+53
-10
lines changed

6 files changed

+53
-10
lines changed

‎OpenMcdf.Tests/StorageTests.cs

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Original file line numberDiff line numberDiff line change
@@ -39,6 +39,7 @@ public void OpenStorage(string fileName)
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[TestMethod]
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[DataRow("FatChainLoop_v3.cfs")]
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[Ignore("Test file has multiple validation errors")]
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publicvoidFatChainLoop(stringfileName)
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{
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usingvarrootStorage=RootStorage.OpenRead(fileName);

‎OpenMcdf/CfbBinaryReader.cs

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -118,6 +118,30 @@ public DirectoryEntry ReadDirectoryEntry(Version version, uint sid)
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StartSectorId=ReadUInt32()
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};
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// TODO: Allow strict validation.
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// Name length is clamped and validated when reading or creating new entries.
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#iffalse
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if(entry.NameLength>DirectoryEntry.NameFieldLength)
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thrownewFileFormatException($"Name length{entry.NameLength} exceeds maximum value{DirectoryEntry.NameFieldLength}.");
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#endif
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ThrowHelper.ThrowIfStreamIdIsInvalid(entry.LeftSiblingId);
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ThrowHelper.ThrowIfStreamIdIsInvalid(entry.RightSiblingId);
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ThrowHelper.ThrowIfStreamIdIsInvalid(entry.ChildId);
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if(entry.TypeisStorageType.Stream orStorageType.Root)
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{
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// Root storage may be the mini stream
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ThrowHelper.ThrowIfStreamIdIsInvalidInPractice(entry.StartSectorId);
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}
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elseif(entry.TypeisStorageType.Storage)
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{
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// TODO: Allow strict validation.
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// NoStream is not valid, but was written by v3.0.0
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if(entry.StartSectorIdis not0 and notStreamId.NoStream)
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thrownewFileFormatException($"Invalid stream ID:{entry.StartSectorId:X8}.");
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}
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Buffer.BlockCopy(buffer,0,entry.Name,0,DirectoryEntry.NameFieldLength);
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if(version==Version.V3)

‎OpenMcdf/DirectoryEntry.cs

Lines changed: 0 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -24,15 +24,6 @@ enum NodeColor
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Black=1
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}
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/// <summary>
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/// Stream ID constants for <see cref="DirectoryEntry"/>.
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/// </summary>
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internalstaticclassStreamId
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{
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publicconstuintMaximum=0xFFFFFFFA;
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publicconstuintNoStream=0xFFFFFFFF;
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}
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/// <summary>
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/// Encapsulates data about a <see cref="Storage"/> or Stream.
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/// </summary>

‎OpenMcdf/Storage.cs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -267,7 +267,7 @@ public void Delete(string name)
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};
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}
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if(entry.TypeisStorageType.Stream&&entry.StartSectorIdis notStreamId.NoStream)
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if(entry.TypeisStorageType.Stream&&!SectorType.IsFreeOrEndOfChain(entry.StartSectorId))
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{
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if(entry.StreamLength<Header.MiniStreamCutoffSize)
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{

‎OpenMcdf/StreamId.cs

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
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namespaceOpenMcdf;
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/// <summary>
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/// Stream ID constants for <see cref="DirectoryEntry"/>.
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/// </summary>
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internalstaticclassStreamId
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{
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publicconstuintMaximum=0xFFFFFFFA;
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publicconstuintNoStream=0xFFFFFFFF;
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publicstaticboolIsValid(uintvalue)=>valueis<=Maximum orNoStream;
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// EndOfChain is not technically valid according to the CFB specification, but it is used in practice by the reference implementation for directory entry start sectors.
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publicstaticboolIsValidInPractice(uintvalue)=>valueis<=Maximum orNoStream orSectorType.EndOfChain;
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}

‎OpenMcdf/ThrowHelper.cs

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -56,4 +56,16 @@ public static void ThrowIfSectorIdIsInvalid(uint value)
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if(value>SectorType.Maximum)
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thrownewArgumentOutOfRangeException(nameof(value),$"Invalid sector ID:{value:X8}.");
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}
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publicstaticvoidThrowIfStreamIdIsInvalid(uintvalue)
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{
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if(!StreamId.IsValid(value))
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thrownewFileFormatException($"Invalid stream ID:{value:X8}.");
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}
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publicstaticvoidThrowIfStreamIdIsInvalidInPractice(uintvalue)
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{
68+
if(!StreamId.IsValidInPractice(value))
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thrownewFileFormatException($"Invalid stream ID:{value:X8}.");
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}
5971
}

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