iemejia commented on code in PR #3861:
URL: https://github.com/apache/avro/pull/3861#discussion_r3567459235
##########
lang/py/avro/io.py:
##########
@@ -599,6 +644,90 @@ def write_timestamp_micros_long(self, datum:
datetime.datetime) -> None:
#
# DatumReader/Writer
#
+#: Environment variable overriding the maximum number of zero-byte-encoded
+#: collection elements (e.g. an array of nulls) to allocate from a single
decode.
+MAX_COLLECTION_ITEMS_ENV = "AVRO_MAX_COLLECTION_ITEMS"
+
+#: Default maximum number of zero-byte-encoded collection elements to allocate.
+#: Elements whose schema encodes to zero bytes (``null``, a zero-length
``fixed``,
+#: or a record with only zero-byte fields) consume no input, so the
bytes-remaining
+#: check cannot bound their count; without a cap a tiny payload can declare a
huge
+#: block count and exhaust memory. A legitimate collection of zero-byte
elements is
+#: small, so this default is generous while still rejecting pathological
input. It
+#: can be raised (or lowered) with the ``AVRO_MAX_COLLECTION_ITEMS``
environment
+#: variable.
+DEFAULT_MAX_COLLECTION_ITEMS = 10_000_000
+
+#: Default structural cap on the number of elements in any array or map (a
+#: collection larger than this is treated as malformed regardless of element
+#: type). Matches the historical ``Integer.MAX_VALUE - 8`` limit. Elements
with a
+#: positive on-wire size are also bounded by the bytes remaining; this cap is
an
+#: additional overflow/defense-in-depth guard. ``AVRO_MAX_COLLECTION_ITEMS``,
when
+#: set, overrides both this and :data:`DEFAULT_MAX_COLLECTION_ITEMS`.
+DEFAULT_MAX_COLLECTION_STRUCTURAL = (1 << 31) - 8
Review Comment:
This was fixed in commit 8279901e00 — the constant is now `(1 << 31) - 1 -
8` (2147483639 = Integer.MAX_VALUE - 8).
##########
lang/py/avro/io.py:
##########
@@ -246,6 +286,11 @@ def read_long(self) -> int:
n = b & 0x7F
shift = 7
while (b & 0x80) != 0:
+ # A 64-bit value needs at most 10 bytes (shifts 0..63); reject an
+ # overlong varint rather than accepting a malformed, arbitrarily
+ # large value.
+ if shift >= 70:
+ raise avro.errors.InvalidAvroBinaryEncoding("Varint is too
long")
b = ord(self.read(1))
n |= (b & 0x7F) << shift
shift += 7
Review Comment:
Fixed — read_long now rejects a 10th byte (shift == 63) with any payload bit
above bit 63 set (`b & 0x7E`), so a 10-byte varint outside the 64-bit range is
rejected.
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