Copilot commented on code in PR #3857:
URL: https://github.com/apache/avro/pull/3857#discussion_r3567378520
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lang/csharp/src/apache/main/File/Codec.cs:
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@@ -29,6 +30,87 @@ namespace Avro.File
/// </summary>
public abstract class Codec
{
+ /// <summary>
+ /// Default upper bound, in bytes, on the size a single data-file
block may
+ /// decompress to. A block with a very high compression ratio (or a
malformed
+ /// block) can otherwise expand to far more memory than its compressed
size.
+ /// Mirrors the Java SDK's decompression limit (AVRO-4247).
Overridable with
+ /// the AVRO_MAX_DECOMPRESS_LENGTH environment variable.
+ /// </summary>
+ public static readonly long DefaultMaxDecompressLength = 200L * 1024 *
1024; // 200 MiB
+
+ /// <summary>
+ /// Name of the environment variable used to override the default
maximum
+ /// decompressed size of a single block.
+ /// </summary>
+ public const string MaxDecompressLengthEnvVar =
"AVRO_MAX_DECOMPRESS_LENGTH";
+
+ /// <summary>
+ /// The maximum number of bytes a single block is allowed to
decompress to.
+ /// </summary>
+ /// <returns>The configured limit, honoring the environment
override.</returns>
+ public static long GetMaxDecompressLength()
+ {
+ var value =
Environment.GetEnvironmentVariable(MaxDecompressLengthEnvVar);
+ if (value != null && long.TryParse(value, NumberStyles.Integer,
CultureInfo.InvariantCulture, out var parsed) && parsed > 0)
+ {
+ return parsed;
+ }
+
+ return DefaultMaxDecompressLength;
+ }
+
+ /// <summary>
+ /// Throws if the given decompressed length exceeds the maximum
allowed.
+ /// </summary>
+ /// <param name="length">The number of decompressed bytes.</param>
+ /// <param name="maxLength">The maximum number of decompressed bytes
allowed.</param>
+ public static void CheckDecompressLength(long length, long maxLength)
+ {
+ if (length > maxLength)
+ {
+ throw new AvroRuntimeException(
+ $"Decompressed block size {length} exceeds the maximum
allowed of {maxLength} bytes. " +
+ $"Set the {MaxDecompressLengthEnvVar} environment variable
to raise the limit.");
+ }
+ }
+
+ /// <summary>
+ /// Copies a decompression stream to the destination, rejecting the
block as
+ /// soon as its decompressed size would exceed <paramref
name="maxLength"/> so
+ /// an over-large (or malicious) block is not fully materialized in
memory.
+ /// </summary>
+ /// <param name="source">The decompression stream to read from.</param>
+ /// <param name="destination">The stream to write the decompressed
data to.</param>
+ /// <param name="maxLength">The maximum number of decompressed bytes
allowed.</param>
+ public static void CopyBounded(Stream source, Stream destination, long
maxLength)
+ {
+ if (source == null)
+ {
+ throw new ArgumentNullException(nameof(source));
+ }
+
+ if (destination == null)
+ {
+ throw new ArgumentNullException(nameof(destination));
+ }
+
+ if (maxLength < 0)
+ {
+ throw new ArgumentOutOfRangeException(nameof(maxLength),
"maxLength must not be negative.");
+ }
+
+ byte[] buffer = new byte[81920];
+ long total = 0;
+ int read;
+ while ((read = source.Read(buffer, 0, buffer.Length)) > 0)
+ {
+ total += read;
+ CheckDecompressLength(total, maxLength);
+ destination.Write(buffer, 0, read);
+ }
Review Comment:
`CopyBounded` uses unchecked `total += read`. If `maxLength` is configured
very large (or `CopyBounded` is used outside block decompression), `total` can
overflow and wrap negative, bypassing `CheckDecompressLength` and potentially
allowing unbounded copying. Use a checked addition (or pre-addition bounds
check) so the limit cannot be bypassed via integer overflow.
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