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authorEric Dumazet <dada1@cosmosbay.com>2007-10-01 13:58:36 -0700
committerDavid S. Miller <davem@sunset.davemloft.net>2007-10-01 21:01:24 -0700
commit9b42c336d06411e6463949d2dac63949f66ff70b (patch)
tree41fbce14cd5a217341649a025622750f71ec71cd /drivers/char/random.c
parent32740ddc1095e5e320bf961dda146bf97bc28adb (diff)
downloadlinux-9b42c336d06411e6463949d2dac63949f66ff70b.tar.bz2
[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 <dada1@cosmosbay.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/char/random.c')
-rw-r--r--drivers/char/random.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 397c714cf2ba..af274e5a25ee 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);