From: Eric Dumazet Date: Mon, 1 Oct 2007 20:58:36 +0000 (-0700) Subject: [TCP]: secure_tcp_sequence_number() should not use a too fast clock X-Git-Tag: v2.6.23~42^2~1 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9b42c336d06411e6463949d2dac63949f66ff70b;p=linux-2.6 [TCP]: secure_tcp_sequence_number() should not use a too fast clock TCP V4 sequence numbers are 32bits, and RFC 793 assumed a 250 KHz clock. In order to follow network speed increase, we can use a faster clock, but we should limit this clock so that the delay between two rollovers is greater than MSL (TCP Maximum Segment Lifetime : 2 minutes) Choosing a 64 nsec clock should be OK, since the rollovers occur every 274 seconds. Problem spotted by Denys Fedoryshchenko [ This bug was introduced by f85958151900f9d30fa5ff941b0ce71eaa45a7de ] Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/drivers/char/random.c b/drivers/char/random.c index 397c714cf2..af274e5a25 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1550,11 +1550,13 @@ __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr, * As close as possible to RFC 793, which * suggests using a 250 kHz clock. * Further reading shows this assumes 2 Mb/s networks. - * For 10 Gb/s Ethernet, a 1 GHz clock is appropriate. - * That's funny, Linux has one built in! Use it! - * (Networks are faster now - should this be increased?) + * For 10 Mb/s Ethernet, a 1 MHz clock is appropriate. + * For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but + * we also need to limit the resolution so that the u32 seq + * overlaps less than one time per MSL (2 minutes). + * Choosing a clock of 64 ns period is OK. (period of 274 s) */ - seq += ktime_get_real().tv64; + seq += ktime_get_real().tv64 >> 6; #if 0 printk("init_seq(%lx, %lx, %d, %d) = %d\n", saddr, daddr, sport, dport, seq);