diff options
| author | Florian Westphal <fw@strlen.de> | 2013-09-20 22:32:55 +0200 |
|---|---|---|
| committer | Jiri Slaby <jslaby@suse.cz> | 2014-03-14 23:00:54 +0100 |
| commit | 6c17205526423c520d8a708d4dbcecbdfe7e9f72 (patch) | |
| tree | e71f5400a38bf2fdd80da71abfb7067ee8fa4c1a /include | |
| parent | 5516d3fa4670849e446c81ddd4c00f0fd09f1173 (diff) | |
tcp: syncookies: reduce cookie lifetime to 128 seconds
commit 8c27bd75f04fb9cb70c69c3cfe24f4e6d8e15906 upstream.
We currently accept cookies that were created less than 4 minutes ago
(ie, cookies with counter delta 0-3). Combined with the 8 mss table
values, this yields 32 possible values (out of 2**32) that will be valid.
Reducing the lifetime to < 2 minutes halves the guessing chance while
still providing a large enough period.
While at it, get rid of jiffies value -- they overflow too quickly on
32 bit platforms.
getnstimeofday is used to create a counter that increments every 64s.
perf shows getnstimeofday cost is negible compared to sha_transform;
normal tcp initial sequence number generation uses getnstimeofday, too.
Reported-by: Jakob Lell <jakob@jakoblell.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Diffstat (limited to 'include')
| -rw-r--r-- | include/net/tcp.h | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h index fa3d50c4b0c7..51dcc6faa561 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -482,6 +482,24 @@ extern int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th, extern struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, struct ip_options *opt); #ifdef CONFIG_SYN_COOKIES +#include <linux/ktime.h> + +/* Syncookies use a monotonic timer which increments every 64 seconds. + * This counter is used both as a hash input and partially encoded into + * the cookie value. A cookie is only validated further if the delta + * between the current counter value and the encoded one is less than this, + * i.e. a sent cookie is valid only at most for 128 seconds (or less if + * the counter advances immediately after a cookie is generated). + */ +#define MAX_SYNCOOKIE_AGE 2 + +static inline u32 tcp_cookie_time(void) +{ + struct timespec now; + getnstimeofday(&now); + return now.tv_sec >> 6; /* 64 seconds granularity */ +} + extern u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th, u16 *mssp); extern __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, |