Copilot commented on code in PR #3855:
URL: https://github.com/apache/avro/pull/3855#discussion_r3567427864
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lang/perl/lib/Avro/DataFileReader.pm:
##########
@@ -207,32 +212,157 @@ sub read_block_header {
return if $codec eq 'null';
- ## we need to read the entire block into memory, to inflate it
- my $nread = read $fh, my $block, $datafile->{block_size} + MARKER_SIZE
- or croak "Error reading from file: $!";
+ ## Guard against an attacker-controlled block_size triggering a huge
+ ## allocation for the compressed block itself, before any decompression
+ ## happens. When the reader is configured with block_max_size, reject a
+ ## block whose declared compressed size exceeds that bound up front.
+ my $block_max = $datafile->{block_max_size};
+ my $block_size = $datafile->{block_size};
+ if (defined $block_max && $block_size > $block_max) {
+ Avro::DataFile::Error::CompressedBlockSize->throw(
+ "Compressed block size $block_size exceeds the configured
block_max_size of $block_max bytes"
+ );
+ }
+
+ ## we need to read the entire block into memory, to inflate it. Verify the
+ ## exact byte count: a short read (truncated/malformed file) would
otherwise
+ ## slip through and surface later as a confusing marker/decompressor error.
+ my $want = $datafile->{block_size} + MARKER_SIZE;
+ my $block;
+ my $nread = read $fh, $block, $want;
+ if (!defined $nread) {
+ croak "Error reading from file: $!";
+ }
+ if ($nread != $want) {
+ croak "Short read: expected $want bytes for the block, got $nread
(truncated file?)";
+ }
## remove the marker
my $marker = substr $block, -(MARKER_SIZE), MARKER_SIZE, '';
$datafile->{block_marker} = $marker;
+ ## The decompressed size of a block is capped to guard against a block with
+ ## a very high compression ratio expanding to far more memory than its
+ ## compressed size. The limit is the AVRO_MAX_DECOMPRESS_LENGTH environment
+ ## variable, or DEFAULT_MAX_DECOMPRESS_LENGTH. (Note: block_max_size is a
+ ## writer-side flush threshold measured in compressed bytes and is not
reused
+ ## here to avoid conflating the two units.)
Review Comment:
The note in this decompression-limit comment says `block_max_size` “is not
reused here”, but `block_max_size` is now reused earlier in the same method as
a *compressed-size* pre-read guard (lines 215–225). Updating the wording to
clarify that `block_max_size` is not reused for the *decompressed-size cap*
(but is used for compressed-size guarding) will prevent reader/writer semantics
confusion.
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