On Thu, 2016-01-14 at 20:23 +0000, Haiyang Zhang wrote: > > For non-random inputs, I used the port selection of iperf that increases > the port number by 2 for each connection. Only send-port numbers are > different, other values are the same. I also tested some other fixed > increment, Toeplitz spreads the connections evenly. For real applications, > if the load came from local area, then the IP/port combinations are > likely to have some non-random patterns. We are not putting code in core networking stack favoring non secure behavior. The +2 behavior for connections from A to B:<fixed port> is something that we will eventually remove in the future. It used to be +1 not a long time ago... Say if we implement the following, https://tools.ietf.org/html/rfc6056#section-3.3.4 The fact that Toeplitz hash has this linear property should not be a valid reason to help hackers to exploit vulnerabilities. In my tests I was using netperf, which randomizes both source & destination ports. This is why I could not reproduce your results based on iperf, which generates 5-tuple in a totally predictable way. This reminds me some drivers had a well known Toeplitz RSS key, allowing attackers to direct their attack on a single queue. I guess we could replace sk_txhash generator by a simple linear allocator and boom, your driver will be pleased. But this is only for a very specific workload. diff --git a/include/net/sock.h b/include/net/sock.h index e830c1006935..949527413cfb 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1689,7 +1689,8 @@ unsigned long sock_i_ino(struct sock *sk); static inline u32 net_tx_rndhash(void) { - u32 v = prandom_u32(); + static u32 last_hash; + u32 v = ++last_hash; // do not care about SMP races. return v ?: 1; } _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
