Ismaël Mejía created AVRO-4275:
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Summary: [C] Signed integer overflow in read_array_value /
read_map_value negation of block_count
Key: AVRO-4275
URL: https://issues.apache.org/jira/browse/AVRO-4275
Project: Apache Avro
Issue Type: Bug
Components: c
Reporter: Ismaël Mejía
Fix For: 1.13.0
The C SDK binary value decoder in {{lang/c/src/value-read.c}} negates an
attacker-controlled {{int64_t block_count}} unconditionally when the count is
negative:
{code:c}
// read_array_value(), line 56:
block_count = block_count * -1;
// read_map_value(), line 92:
block_count = block_count * -1;
{code}
Per the Avro spec, a negative block count means the absolute value of the
count, followed by a block byte-size prefix. However, when {{block_count ==
INT64_MIN}} (zigzag bytes {{FF FF FF FF FF FF FF FF FF 01}}), the negation is
signed-integer overflow — undefined behavior in C (CWE-190). On x86_64 / gcc
-O0 the result wraps back to {{INT64_MIN}}. The subsequent loop:
{code:c}
for (i = 0; i < (size_t) block_count; i++, index++) {
avro_value_append(dest, &child, NULL);
...
}
{code}
casts the still-negative value to {{(size_t)0x8000000000000000}} (~9.2
quintillion iterations), driving {{avro_raw_array_ensure_size}} doubling
reallocs until address-space exhaustion.
*Impact:* A single ~11-byte malformed Avro binary frame can wedge a decoding
thread and exhaust process memory (DoS). This is the C SDK counterpart to the
Java SDK pattern fixed in 1.11.3 via
{{SystemLimitException.checkMaxCollectionLength}} (CVE-2023-39410).
*Affected versions:* All releases of the C SDK up to and including 1.12.0.
*Fix:* Replace the unsafe {{block_count * -1}} with the overflow-safe idiom
{{-(block_count + 1) + 1}} (same approach used in the C++ fix AVRO-4228),
followed by a guard that rejects the result if it remains non-positive:
{code:c}
block_count = -(block_count + 1) + 1;
if (block_count <= 0) {
avro_set_error("Invalid array block count");
return EINVAL;
}
{code}
This eliminates the undefined behavior, rejects {{INT64_MIN}} gracefully, and
preserves correct handling of all legitimate negative block counts.
*Reported by:* Brian Lee (Georgia Tech SSLab)
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