Copilot commented on code in PR #3862:
URL: https://github.com/apache/avro/pull/3862#discussion_r3566582745
##########
lang/ruby/lib/avro/io.rb:
##########
@@ -496,12 +550,98 @@ def skip_record(writers_schema, decoder)
end
private
- def skip_blocks(decoder, &blk)
+ # Minimum number of bytes a single value of the given schema can occupy
on
+ # the wire. Used to reject an array/map block count that could not be
+ # backed by the bytes remaining. A type that can encode to zero bytes
+ # (null) returns 0, which disables the check for it (so an array of nulls
+ # is not falsely rejected).
+ def min_bytes_per_element(schema, visited = nil)
+ visited ||= {}.compare_by_identity
+ case schema.type_sym
+ when :null then 0
+ when :float then 4
+ when :double then 8
+ when :fixed then schema.size
+ when :record, :error, :request
+ return 0 if visited[schema]
+ visited[schema] = true
+ total = schema.fields.sum { |field|
min_bytes_per_element(field.type, visited) }
+ visited.delete(schema)
+ total
+ else
+ # boolean, int, long, bytes, string, enum, union, array, map: >= 1
byte
+ # (a union encodes at least a 1-byte branch index).
+ 1
+ end
+ end
+
+ # Reject a collection (array or map) block that could drive an unbounded
+ # allocation, before iterating. A block whose declared element count
could
+ # not be backed by the bytes actually remaining is rejected; a block of
+ # zero-byte elements (where the bytes-remaining check does not apply) is
+ # bounded by a cumulative item cap; and every collection is bounded by a
+ # structural cap. Returns the running total across blocks.
+ #
+ # Both limits default to the same values as the other Avro SDKs and can
be
+ # overridden (to a single value capping both) via the
+ # AVRO_MAX_COLLECTION_ITEMS environment variable.
+ DEFAULT_MAX_COLLECTION_ITEMS = 10_000_000 # Zero-byte element cap.
+ DEFAULT_MAX_COLLECTION_STRUCTURAL = 2147483639 # Integer.MAX_VALUE - 8.
+
+ def collection_limits
+ env = Integer(ENV['AVRO_MAX_COLLECTION_ITEMS'], exception: false)
+ if env && env >= 0
+ [env, env]
+ else
+ [DEFAULT_MAX_COLLECTION_ITEMS, DEFAULT_MAX_COLLECTION_STRUCTURAL]
+ end
+ end
+
+ def ensure_collection_available(decoder, total, count,
min_bytes_per_element)
+ # A negative count is corrupt/malicious data (it can also arise from
+ # overflow when negating a negative block count); reject it explicitly.
+ raise CollectionSizeError, "Invalid negative collection block count:
#{count}" if count < 0
Review Comment:
The comment about a negative count arising from overflow when negating a
negative block count is not accurate in Ruby (Integer is arbitrary-precision,
so negation doesn’t overflow). This can confuse future maintainers about when
`count < 0` is actually possible here.
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