fix: bound decodeString/decodeBytes growth to avoid OOM on untrusted length#4
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moshap-firebolt wants to merge 1 commit into
Open
fix: bound decodeString/decodeBytes growth to avoid OOM on untrusted length#4moshap-firebolt wants to merge 1 commit into
moshap-firebolt wants to merge 1 commit into
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…length Avro string/bytes values carry a length prefix that is attacker controlled when the Avro data is untrusted (e.g. Iceberg manifest files). decodeString and decodeBytes resized their destination to that full length in one call, so a malformed multi-GiB length triggered a huge allocation (OOM) before a single byte was read and the stream was found to be far shorter. Grow the destination in bounded 1 MiB chunks instead: a bogus length now fails on the "EOF reached" thrown by readBytes() after only a bounded allocation, while well-formed values still read in full.
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Review pass: this change looks correct to me. The bounded 1 MiB chunk growth in decodeString/decodeBytes prevents attacker-controlled OOM from oversized length prefixes while still streaming valid payloads correctly. I also checked that all PR checks are passing. |
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Problem
BinaryDecoder::decodeString/decodeBytesread a length prefix and thenresize()the destination to that full length in a single call before readingany bytes. The length prefix is attacker-controlled when the Avro data is
untrusted (e.g. Iceberg manifest files read by PackDB). A malformed multi-GiB
length triggers a huge allocation — an OOM — before the decoder discovers the
stream is far shorter than the declared length.
Surfaced by PackDB's
iceberg_avrolibFuzzer harness: a mutated length prefixin the Avro file's metadata map (
map<string,bytes>) drove a ~2 GiBstd::string::resizeinreadHeader(), reported as a libFuzzer OOM.Fix
Grow the destination in bounded 1 MiB chunks. A bogus length now fails on the
"EOF reached"exception thrown byreadBytes()after only a boundedallocation, while well-formed values still read in full (identical bytes).
Test
iceberg_avrofuzzer, then confirmedthe crash input runs clean (exit 0, 2 ms) with this change.