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Commit 9b42c336 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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[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 f8595815 ]

Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 32740ddc

drivers/char/random.c

+6 −4
Original line number Diff line number Diff line
@@ -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);