Reject empty extension sequences and generalize input-stream limit detection#143
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…tection Two independent ASN.1 hardening changes. 1. Minimum sequence-size restriction on X.509 extensions TCrlDistPoint and TExtendedKeyUsage now reject an empty sequence (< 1 element) in both their decode (IAsn1Sequence) and array constructors, via TAsn1Utilities.CheckSequenceSize(seq, 1, Int32.MaxValue). A malformed extension with no elements now raises EArgumentCryptoLibException instead of constructing a degenerate object. Both classes already stored the sequence and mapped on demand, so no storage change was needed. Adds TestCrlDistPointRejectsEmptySequence and TestExtendedKeyUsageRejectsEmptySequence to X509ExtensionsTests. 2. TStreamUtilities.TryGetAvailable and use in FindLimit Add TryGetAvailable(stream, out available): best-effort remaining bytes for a seekable stream (Max(0, Size - Position)), guarded so a stream that throws is treated as unavailable. TAsn1InputStream.FindLimit now uses it, replacing the TFixedBufferStream-specific branch (GetFixedBufferStreamLimit removed): any seekable stream gets an available-based limit, not just the fixed buffer. TFixedBufferStream is seekable, so its limit is unchanged; byte-array input still yields a tight bound. Corrects the InputStreamTests dummy: it modelled "unknown/non-seekable" but its Seek was a no-op returning 0, making it look like a seekable empty stream. It now inherits TBaseInputStream (CanSeek = False) with a raising Seek, so it honestly exercises FindLimit's fallback; TestNegativeMaxLimitClampsFindLimit uses it to actually reach the clamp path.
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Two independent ASN.1 hardening changes.
Minimum sequence-size restriction on X.509 extensions TCrlDistPoint and TExtendedKeyUsage now reject an empty sequence (< 1 element) in both their decode (IAsn1Sequence) and array constructors, via TAsn1Utilities.CheckSequenceSize(seq, 1, Int32.MaxValue). A malformed extension with no elements now raises EArgumentCryptoLibException instead of constructing a degenerate object. Both classes already stored the sequence and mapped on demand, so no storage change was needed. Adds TestCrlDistPointRejectsEmptySequence and TestExtendedKeyUsageRejectsEmptySequence to X509ExtensionsTests.
TStreamUtilities.TryGetAvailable and use in FindLimit Add TryGetAvailable(stream, out available): best-effort remaining bytes for a seekable stream (Max(0, Size - Position)), guarded so a stream that throws is treated as unavailable. TAsn1InputStream.FindLimit now uses it, replacing the TFixedBufferStream-specific branch (GetFixedBufferStreamLimit removed): any seekable stream gets an available-based limit, not just the fixed buffer. TFixedBufferStream is seekable, so its limit is unchanged; byte-array input still yields a tight bound.
Corrects the InputStreamTests dummy: it modelled "unknown/non-seekable" but its Seek was a no-op returning 0, making it look like a seekable empty stream. It now inherits TBaseInputStream (CanSeek = False) with a raising Seek, so it honestly exercises FindLimit's fallback; TestNegativeMaxLimitClampsFindLimit uses it to actually reach the clamp path.