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Subject[PATCH v3 net 3/7] tcp: resalt the secret every 10 seconds
Date
From: Eric Dumazet <edumazet@google.com>

In order to limit the ability for an observer to recognize the source
ports sequence used to contact a set of destinations, we should
periodically shuffle the secret. 10 seconds looks effective enough
without causing particular issues.

Cc: Moshe Kol <moshe.kol@mail.huji.ac.il>
Cc: Yossi Gilad <yossi.gilad@mail.huji.ac.il>
Cc: Amit Klein <aksecurity@gmail.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
net/core/secure_seq.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 55aa5cc258e3..5f85e01d4093 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -22,6 +22,8 @@
static siphash_aligned_key_t net_secret;
static siphash_aligned_key_t ts_secret;

+#define EPHEMERAL_PORT_SHUFFLE_PERIOD (10 * HZ)
+
static __always_inline void net_secret_init(void)
{
net_get_random_once(&net_secret, sizeof(net_secret));
@@ -100,11 +102,13 @@ u64 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
const struct {
struct in6_addr saddr;
struct in6_addr daddr;
+ unsigned int timeseed;
__be16 dport;
} __aligned(SIPHASH_ALIGNMENT) combined = {
.saddr = *(struct in6_addr *)saddr,
.daddr = *(struct in6_addr *)daddr,
- .dport = dport
+ .timeseed = jiffies / EPHEMERAL_PORT_SHUFFLE_PERIOD,
+ .dport = dport,
};
net_secret_init();
return siphash(&combined, offsetofend(typeof(combined), dport),
@@ -145,8 +149,10 @@ EXPORT_SYMBOL_GPL(secure_tcp_seq);
u64 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
net_secret_init();
- return siphash_3u32((__force u32)saddr, (__force u32)daddr,
- (__force u16)dport, &net_secret);
+ return siphash_4u32((__force u32)saddr, (__force u32)daddr,
+ (__force u16)dport,
+ jiffies / EPHEMERAL_PORT_SHUFFLE_PERIOD,
+ &net_secret);
}
EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
#endif
--
2.17.5
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