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Base64.Decode: fixed latent bug for invalid input that is less than a block-size #79952

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Merged
merged 2 commits into from
Jan 4, 2023
Merged

Base64.Decode: fixed latent bug for invalid input that is less than a block-size #79952

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9743543
Tests
gfoidl Dec 24, 2022
4da5369
Fix
gfoidl Dec 24, 2022
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13 changes: 13 additions & 0 deletions src/libraries/System.Memory/tests/Base64/Base64DecoderUnitTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,19 @@ public void BasicDecodingInvalidInputLength()
}
}

[Fact]
public void BasicDecodingInvalidInputWithSlicedSource()
{
ReadOnlySpan<byte> source = stackalloc byte[] { (byte)'A', (byte)'B', (byte)'C', (byte)'D' };
Span<byte> decodedBytes = stackalloc byte[128];

source = source[..3]; // now it's invalid as only 3 bytes are present

Assert.Equal(OperationStatus.InvalidData, Base64.DecodeFromUtf8(source, decodedBytes, out int consumed, out int decodedByteCount));
Assert.Equal(0, consumed);
Assert.Equal(0, decodedByteCount);
}

[Fact]
public void BasicDecodingWithFinalBlockFalse()
{
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2 changes: 1 addition & 1 deletion src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Decoder.cs
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Expand Up @@ -101,7 +101,7 @@ public static unsafe OperationStatus DecodeFromUtf8(ReadOnlySpan<byte> utf8, Spa
}

ref sbyte decodingMap = ref MemoryMarshal.GetReference(DecodingMap);
srcMax = srcBytes + (uint)maxSrcLength;
srcMax = srcBytes + maxSrcLength;
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@gfoidl gfoidl Dec 24, 2022 •
edited
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The uint-cast was there to avoid the movsxd (on x86), so removing the cast will introduce the movsxd and I expect that be cheaper than having a if to guard the loop.

PS: this is a reason why I dislike walking with pointers around (ptr++), and prefer index-based addressing (ptr[i] or ptr + offset) as it's clearer where to start and where to end.


while (src < srcMax)
{
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