Copilot commented on code in PR #3850:
URL: https://github.com/apache/avro/pull/3850#discussion_r3567557088
##########
lang/py/avro/codecs.py:
##########
@@ -123,7 +173,22 @@ def decompress(readers_decoder: avro.io.BinaryDecoder) ->
avro.io.BinaryDecoder:
data = readers_decoder.read_bytes()
# -15 is the log of the window size; negative indicates
# "raw" (no zlib headers) decompression. See zlib.h.
- uncompressed = zlib.decompress(data, -15)
+ limit = _max_decompress_length()
+ decompressor = zlib.decompressobj(-15)
+ # Request at most limit + 1 bytes so that an over-large block is
detected
+ # without allocating the whole (potentially huge) output. Accumulate
into
+ # a bytearray so the flush() output is appended in place rather than
+ # creating an extra full-size copy of the already-decompressed data.
+ uncompressed = bytearray(decompressor.decompress(data, limit + 1))
+ if len(uncompressed) > limit:
+ _raise_decompression_too_large(limit)
+ uncompressed += decompressor.flush()
+ if len(uncompressed) > limit:
+ _raise_decompression_too_large(limit)
+ if not decompressor.eof:
+ # The end-of-stream marker was not reached: the block is truncated
or
+ # corrupt. zlib.decompress() used to raise for this; preserve that.
+ raise avro.errors.InvalidAvroBinaryEncoding("Truncated or corrupt
deflate block")
Review Comment:
`DeflateCodec.decompress()` caps `decompress()` output with `max_length`,
but `decompressor.flush()` is currently unbounded. If the compressed input
expands beyond the limit, the excess output can be materialized during
`flush()` (allocating far past the configured cap) before the size check runs,
which defeats the decompression-bomb protection goal.
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