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Fix overflow in GetHexStringCore #111296

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Merged
merged 3 commits into from
Jan 13, 2025
Merged

Fix overflow in GetHexStringCore #111296

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fb8fd98
Fix overflow in GetHexStringCore
vcsjones Jan 11, 2025
5302eaa
Merge branch 'main' into fix-overflow-gethexstring
vcsjones Jan 11, 2025
ccedf6a
Add a comment explaining the right unsigned shift.
vcsjones Jan 12, 2025
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4 changes: 3 additions & 1 deletion ...es/System.Security.Cryptography/src/System/Security/Cryptography/RandomNumberGenerator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -313,7 +313,9 @@ private static void GetHexStringCore(Span<char> destination, bool lowercase)

// Don't overfill the buffer if the destination is smaller than the buffer size. We need to round up when
// when dividing by two to account for an odd-length destination.
int needed = (destination.Length + 1) / 2;
// Adding one to a span of length int.MaxValue may overflow. This is handled by the unsigned shift to the right
// which will correct the overflow.
int needed = (destination.Length + 1) >>> 1;
Span<byte> remainingRandom = randomBuffer.Slice(0, Math.Min(RandomBufferSize, needed));
RandomNumberGenerator.Fill(remainingRandom);

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