On Wed, Feb 12, 2014 at 3:35 AM, Daniel Borkmann <[email protected]> wrote: > (please cc netdev) > > On 02/12/2014 11:25 AM, Quinn Wood wrote: >> >> If program on host A spoofs the source address of an outgoing IPv4 packet >> then >> places that address in the first 32 bits of a UDP payload, a program on >> host B >> that is aware of these behaviors can still reply to the program on host A. >> [1] >> >> Continuing with this approach the program on host A could encrypt the UDP >> pay- >> load in a way that the program on host B can decrypt, and effectively >> reduce >> the ability of others in the wide network to passively determine who host >> A is >> sending transmissions to while simultaneously ensuring the program on host >> B >> can respond to the program on host A. [2] >> >> I'm uncertain how to proceed if I want to use TCP for stateful >> connections. >> The requirement of a handshake before data is handed off to the program >> means >> this approach won't work out of the box. I'm looking for any insight folks >> may >> have regarding this. >> >> My original approach to the handshake included setting one of the reserved >> bits in the TCP header to indicate the first 32 bits of the payload were >> the >> real source address. However this would be reliant on SYN packets >> containing >> a payload. Does the Linux kernel allow this? For 3.7+ you can use TCP Fast Open.
For a quick trial experiment, you can just set sysctl net.ipv4.tcp_fastopen=0x603 on both end hosts and use sendmsg(..., MSG_FASTOPEN) instead of connect() then send(). the sendmsg() will behave as a combo call of connect() and send() and return similar errno. accept() will return after data in the SYN is received instead of after handshake is completed. >> >> - >> >> [1] Barring any non store-and-forward network behavior like dropping >> packets >> with questionable source addresses. Considering recent NTP-related >> news >> this seems to be a not-entirely common activity :) >> [2] This is of course reliant on both programs knowing the proper key for >> the >> other. > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
