Panic within QUICRandomFrames

[Diniboy1123]

Hey,

This is a great library, however there seems to be an issue with the QUICRandomFrames algorithm I am sometimes running into. It throws: panic: crypto/rand: argument to Int is <= 0

Based on the stacktrace it occurs at this line:

uquic/u_quic_frames.go

Line 253 in 98f5a5d

lenCRYPTO, err := cryptoSafeRandUint64(1, lenCryptoData-(numCRYPTO-i-2))

I modified the surrounding code blindly to avoid overflows:

lenCryptoData := uint64(len(cryptoData))
offsetCryptoData := uint64(0)
for i := uint64(0); i < numCRYPTO-1; i++ { // select n-1 times, since the last one must be the remaining
	// randomly select length of CRYPTO frame.
	// Length must be at least 1 byte and at most the remaining length of cryptoData minus the remaining number of CRYPTO frames.
	// i.e. len in [1, len(cryptoData)-offsetCryptoData-(numCRYPTO-i-2))
	log.Printf("lenCryptoData: %d, offsetCryptoData: %d, numCRYPTO: %d, i: %d\n", lenCryptoData, offsetCryptoData, numCRYPTO, i)
	remainingCrypto := lenCryptoData - (numCRYPTO - i - 2)

	// check if it overflows uint64
	if remainingCrypto > 0xFFFFFFFF || remainingCrypto == 0 {
		log.Printf("remainingCrypto overflow: %d\n", remainingCrypto)
		break
	} else {
		log.Printf("remainingCrypto: %d\n", remainingCrypto)
	}

	lenCRYPTO, err := cryptoSafeRandUint64(1, remainingCrypto)
	if err != nil {
		return nil, err
	}
	frameList = append(frameList, QUICFrameCrypto{Offset: int(offsetCryptoData), Length: int(lenCRYPTO)})
	offsetCryptoData += lenCRYPTO
	lenCryptoData -= lenCRYPTO
}

And in the problematic case I saw this in the logs:

2024/12/20 03:59:19 lenCryptoData: 508, offsetCryptoData: 0, numCRYPTO: 5, i: 0
2024/12/20 03:59:19 remainingCrypto: 505
2024/12/20 03:59:19 lenCryptoData: 69, offsetCryptoData: 439, numCRYPTO: 5, i: 1
2024/12/20 03:59:19 remainingCrypto: 67
2024/12/20 03:59:19 lenCryptoData: 54, offsetCryptoData: 454, numCRYPTO: 5, i: 2
2024/12/20 03:59:19 remainingCrypto: 53
2024/12/20 03:59:19 lenCryptoData: 31, offsetCryptoData: 477, numCRYPTO: 5, i: 3
2024/12/20 03:59:19 remainingCrypto: 31
2024/12/20 03:59:19 lenCryptoData: 0, offsetCryptoData: 0, numCRYPTO: 6, i: 0
2024/12/20 03:59:19 remainingCrypto overflow: 18446744073709551612

It doesn't always happen, but when it does, the program panics...

[mingyech]

Wait I just realized that this is a different issue from the PR above 🤦