Copilot commented on code in PR #3851:
URL: https://github.com/apache/avro/pull/3851#discussion_r3567457102
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lang/ruby/lib/avro/data_file.rb:
##########
@@ -339,24 +372,55 @@ def codec_name; 'snappy'; end
def decompress(data)
load_snappy!
- crc32 = data.slice(-4..-1).unpack('N').first
- uncompressed = Snappy.inflate(data.slice(0..-5))
-
- if crc32 == Zlib.crc32(uncompressed)
- uncompressed
- else
- # older versions of avro-ruby didn't write the checksum, so if it
- # doesn't match this must assume that it wasn't there and return
- # the entire payload uncompressed.
- Snappy.inflate(data)
+ # The Snappy block header declares the uncompressed length as a varint;
+ # reject an over-large block before allocating for it.
+ limit = DataFile.max_decompress_length
+ declared = self.class.snappy_declared_length(data)
+ # Fail closed: a block whose length header cannot be parsed is
malformed
+ # and must not be handed to the decompressor with the guard bypassed.
+ if declared.nil?
+ raise DataFileError, "Snappy block has an unparseable length header"
end
+ if declared > limit
+ raise DecompressionSizeError, "Decompressed block size exceeds the
maximum allowed of #{limit} bytes"
+ end
+ # A well-formed block ends with a 4-byte CRC32 trailer. If the buffer
is
+ # too short to contain it, don't slice past the start (data[-4..-1]
would
+ # be nil and raise on unpack); treat it as a legacy no-checksum block.
+ if data.bytesize >= 4
+ crc32 = data.slice(-4..-1).unpack('N').first
+ uncompressed = Snappy.inflate(data.slice(0..-5))
Review Comment:
The CRC32-path guard allows `data.bytesize == 4`, but then
`data.slice(0..-5)` returns nil (end index is out of range), which can raise a
TypeError/NoMethodError rather than a controlled Avro error. Require at least 5
bytes before attempting to strip the 4-byte trailer, and use `byteslice(0,
data.bytesize - 4)` to avoid fragile negative-range slicing.
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