Bug: u32 underflow in Unix timestamp calculation

[fasuizu-br]

Description

In get_unix_time_by_addr(), the timestamp conversion subtracts SNTP_TIME_OFFSET (2,208,988,800) from raw_secs (u32) before casting to i64:

Ok((raw_secs - SNTP_TIME_OFFSET) as i64)

If a malicious or malfunctioning NTP server returns raw_secs < SNTP_TIME_OFFSET, the subtraction causes a u32 underflow (wrapping around), resulting in a completely wrong Unix timestamp instead of an error.

Suggested fix

Cast to i64 before the subtraction:

Ok((raw_secs as i64) - (SNTP_TIME_OFFSET as i64))

Or use checked arithmetic:

raw_secs.checked_sub(SNTP_TIME_OFFSET)
    .map(|v| v as i64)
    .ok_or_else(|| Error::new(
        ErrorKind::InvalidData,
        "Server returned timestamp before SNTP epoch",
    ))