Copilot commented on code in PR #3855:
URL: https://github.com/apache/avro/pull/3855#discussion_r3568125921
##########
lang/perl/lib/Avro/DataFileReader.pm:
##########
@@ -203,36 +208,190 @@ sub read_block_header {
$datafile->{block_size} = Avro::BinaryDecoder->decode_long(
undef, undef, $fh,
);
+ ## Both are Avro long (zigzag) values, so a malformed/truncated file can
+ ## yield negatives. A negative block_size would flow into $want and a
+ ## negative-length read; a negative object_count is equally nonsensical.
+ ## Reject both before first use.
+ if ($datafile->{object_count} < 0) {
+ croak "Invalid negative object count: $datafile->{object_count}";
+ }
+ if ($datafile->{block_size} < 0) {
+ croak "Invalid negative block size: $datafile->{block_size}";
+ }
$datafile->{block_start} = tell $fh;
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. Read in
+ ## bounded chunks (rather than a single read of $want bytes, which would
+ ## pre-extend the buffer to the attacker-controlled block_size before a
short
+ ## read is detected) and verify the exact byte count afterward: 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 $chunk_size = 64 * 1024;
+ while (bytes::length($block) < $want) {
+ my $need = $want - bytes::length($block);
+ $need = $chunk_size if $need > $chunk_size;
+ my $nread = read $fh, my $buf, $need;
+ if (!defined $nread) {
+ croak "Error reading from file: $!";
+ }
+ last if $nread == 0; # EOF
+ $block .= $buf;
+ }
+ if (bytes::length($block) != $want) {
+ croak "Short read: expected $want bytes for the block, got "
+ . bytes::length($block) . " (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; it is used
above
+ ## as a compressed-size pre-read guard, but is not reused here for the
+ ## decompressed-size cap, to avoid conflating the two units.)
+ my $limit = _max_decompress_length();
+
## this is our new reader
$datafile->{reader} = do {
if ($codec eq 'deflate') {
- IO::Uncompress::RawInflate->new(\$block);
+ my $z = IO::Uncompress::RawInflate->new(\$block)
+ or croak "Error inflating block:
$IO::Uncompress::RawInflate::RawInflateError";
+ my $uncompressed = _inflate_bounded($z, $limit);
+ _open_decompressed(\$uncompressed);
}
elsif ($codec eq 'bzip2') {
- my $uncompressed;
- bunzip2 \$block => \$uncompressed;
- do { open $fh, '<', \$uncompressed; $fh };
+ my $z = IO::Uncompress::Bunzip2->new(\$block)
+ or croak "Error decompressing bzip2 block:
$IO::Uncompress::Bunzip2::Bunzip2Error";
+ my $uncompressed = _inflate_bounded($z, $limit);
+ _open_decompressed(\$uncompressed);
}
elsif ($codec eq 'zstandard') {
- do { open $fh, '<', \(decompress(\$block)); $fh };
+ my $uncompressed = _zstd_decompress_bounded(\$block, $limit);
+ _open_decompressed(\$uncompressed);
}
};
return;
}
+## Open an in-memory read handle over the decompressed block, surfacing any
+## failure via croak rather than leaving $datafile->{reader} undefined (which
+## would fail later with a less clear error). The handle keeps a reference to
+## the scalar, so the caller's buffer stays alive for the lifetime of the read.
+sub _open_decompressed {
+ my ($uncompressed_ref) = @_;
+ open my $fh, '<', $uncompressed_ref
+ or croak "Error opening decompressed block for reading: $!";
+ return $fh;
+}
+
+## Read from a streaming decompressor in chunks, rejecting the block as soon as
+## its decompressed size would exceed $limit so an over-large (or malicious)
+## block is not fully materialized in memory. Each read is sized to the
+## remaining budget (capped at 64 KiB) so the buffer overshoots $limit by at
+## most one byte before the check fires.
+sub _inflate_bounded {
+ my ($z, $limit) = @_;
+ my $uncompressed = '';
+ my $chunk;
+ my $status;
+ while (1) {
+ my $budget = $limit - bytes::length($uncompressed) + 1;
+ my $to_read = $budget < 65536 ? $budget : 65536;
+ $status = $z->read($chunk, $to_read);
+ last unless defined $status && $status > 0;
+ $uncompressed .= $chunk;
+ _check_decompress_length(bytes::length($uncompressed), $limit);
+ }
+ if (!defined $status || $status < 0) {
+ croak "Error decompressing block: " . $z->error;
+ }
+ return $uncompressed;
+}
+
+## Streaming zstandard decompression, bounded the same way as _inflate_bounded
so
+## a high-ratio block is rejected before its full form is materialized.
+sub _zstd_decompress_bounded {
+ my ($block_ref, $limit) = @_;
+ # Load the zstandard decompressor lazily so the reader still loads and
works
+ # for other codecs when Compress::Zstd::Decompressor is unavailable (e.g.
an
+ # older Compress::Zstd distribution that lacks the Decompressor submodule).
+ unless (eval { require Compress::Zstd::Decompressor; 1 }) {
+ Avro::DataFile::Error::UnsupportedCodec->throw(
+ "Cannot read zstandard-compressed block:
Compress::Zstd::Decompressor is not available: $@"
+ );
+ }
Review Comment:
The lazy `require` for Compress::Zstd::Decompressor uses `eval { ... }`
without localizing `$@`, which can clobber the caller’s `$@` (it will be
cleared on success). Localize `$@` and capture the require error in a lexical
before building the UnsupportedCodec message.
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