[PATCH 4.14 16/25] tcp: resalt the secret every 10 seconds

Greg Kroah-Hartman
2022-05-16T19:42:52Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 4dfa9b438ee34caca4e6a4e5e961641807367f6f ]

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>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 7232274de334..17683aea8a35 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -22,6 +22,8 @@
static siphash_key_t net_secret __read_mostly;
static siphash_key_t ts_secret __read_mostly;

+#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 @@ u32 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),
@@ -144,8 +148,10 @@ u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
u32 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
--
2.35.1