[PATCH v4] net: tftp: Add client support for RFC 7440

[Ravik Hasija <rahasij@linux.microsoft.com>]

Ramon Fried-4 wrote
> +			if (strcmp((char *)pkt + i,  "windowsize") == 0) {
> For servers that doesnt support windowsize option the above check could
> result in accessing memory outside of valid range. Please check if (i+11)
> < len before comparing the strings.
> 
> 
> +
> +		if (ntohs(*(__be16 *)pkt) != (ushort)(tftp_cur_block + 1)) {
> +			debug("Received unexpected block: %d, expected: %d\n",
> +			      ntohs(*(__be16 *)pkt),
> +			      (ushort)(tftp_cur_block + 1));
> +			/*
> +			 * If one packet is dropped most likely
> +			 * all other buffers in the window
> +			 * that will arrive will cause a sending NACK.
> +			 * This just overwellms the server, let's just send one.
> +			 */
> +			if (tftp_last_nack != tftp_cur_block) {
> +				tftp_send();
> +				tftp_last_nack = tftp_cur_block;
> +				tftp_next_ack = (ushort)(tftp_cur_block +
> +							 tftp_windowsize);
> +			}
> +			break;
> +		}
> +
> +		tftp_cur_block++;
> 
> Monotonically increasing the tftp_cur_block will cause error for cases
> where sequence number wraps around as tftp_cur_block is ulong, thus during
> wraparound the check ntohs(*(__be16 *)pkt) != (ushort)(tftp_cur_block + 1)
> will fail and incorrectly generate ACK, and the connection will eventually
> be terminated once the retry is exhausted. Please modulo the increment
> with TFTP_SEQUENCE_SIZE.  
> -- 
> 2.26.2

Quoted from: 
http://u-boot.10912.n7.nabble.com/PATCH-v4-net-tftp-Add-client-support-for-RFC-7440-tp412754.html




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