[jira] [Created] (AVRO-4275) [C] Signed integer overflow in read_array_value / read_map_value negation of block_count

["Ismaël Mejía (Jira)" <ji...@apache.org>]

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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