iemejia opened a new pull request, #3849:
URL: https://github.com/apache/avro/pull/3849
## What is the purpose of the change
`GenericReader::read()` decodes arrays and maps by calling
`r.resize(r.size() + m)`, where `m` is the block count returned by
`Decoder::arrayStart()` / `mapStart()` / `arrayNext()` / `mapNext()`.
Because the
block count is read from the (potentially untrusted or truncated) input, a
very
large or malformed count could eagerly allocate an unbounded vector before
any
element is read (items such as `null` occupy no bytes on the wire).
This validates the block count — per block and cumulatively — against a
configurable maximum before resizing, mirroring the Java SDK's collection
item
limit (`org.apache.avro.limits.collectionItems.maxLength`, AVRO-3819). The
limit
defaults to `2^31 - 8` items and can be overridden with the
`AVRO_MAX_COLLECTION_ITEMS` environment variable. Exceeding it throws an
`avro::Exception` before allocating.
This is part of the umbrella issue AVRO-4277.
## Verifying this change
This change added tests and can be verified as follows:
- Added `testArrayBlockCountIsBounded` and `testMapBlockCountIsBounded` in
`lang/c++/test/CodecTests.cc` covering: a single block count above the
limit
(array and map), a cumulative limit across blocks, a negative block count
bounded by its absolute value, and a within-limit collection still decoding
correctly.
- Run: `ctest -R CodecTests` (852 cases pass)
## Documentation
- Does this pull request introduce a new feature? (no — hardening/robustness)
- If yes, how is the feature documented? (not applicable; the new
`AVRO_MAX_COLLECTION_ITEMS` environment variable is documented in code
comments)
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