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authorEric Dumazet <edumazet@google.com>2017-05-05 06:56:54 -0700
committerDavid S. Miller <davem@davemloft.net>2017-05-05 12:00:11 -0400
commit84b114b98452c431299d99c135f751659e517acb (patch)
tree53778bfd4964bed65ac40a9c1c57a73f21cb9664 /net/core
parent9051247dcf9ecee156d2ddac39a4f1ca591f8428 (diff)
downloadlinux-84b114b98452c431299d99c135f751659e517acb.tar.bz2
tcp: randomize timestamps on syncookies
Whole point of randomization was to hide server uptime, but an attacker can simply start a syn flood and TCP generates 'old style' timestamps, directly revealing server jiffies value. Also, TSval sent by the server to a particular remote address vary depending on syncookies being sent or not, potentially triggering PAWS drops for innocent clients. Lets implement proper randomization, including for SYNcookies. Also we do not need to export sysctl_tcp_timestamps, since it is not used from a module. In v2, I added Florian feedback and contribution, adding tsoff to tcp_get_cookie_sock(). v3 removed one unused variable in tcp_v4_connect() as Florian spotted. Fixes: 95a22caee396c ("tcp: randomize tcp timestamp offsets for each connection") Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Florian Westphal <fw@strlen.de> Tested-by: Florian Westphal <fw@strlen.de> Cc: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/secure_seq.c31
1 files changed, 19 insertions, 12 deletions
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 6bd2f8fb0476..ae35cce3a40d 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -24,9 +24,13 @@ static siphash_key_t ts_secret __read_mostly;
static __always_inline void net_secret_init(void)
{
- net_get_random_once(&ts_secret, sizeof(ts_secret));
net_get_random_once(&net_secret, sizeof(net_secret));
}
+
+static __always_inline void ts_secret_init(void)
+{
+ net_get_random_once(&ts_secret, sizeof(ts_secret));
+}
#endif
#ifdef CONFIG_INET
@@ -47,7 +51,7 @@ static u32 seq_scale(u32 seq)
#endif
#if IS_ENABLED(CONFIG_IPV6)
-static u32 secure_tcpv6_ts_off(const __be32 *saddr, const __be32 *daddr)
+u32 secure_tcpv6_ts_off(const __be32 *saddr, const __be32 *daddr)
{
const struct {
struct in6_addr saddr;
@@ -60,12 +64,14 @@ static u32 secure_tcpv6_ts_off(const __be32 *saddr, const __be32 *daddr)
if (sysctl_tcp_timestamps != 1)
return 0;
+ ts_secret_init();
return siphash(&combined, offsetofend(typeof(combined), daddr),
&ts_secret);
}
+EXPORT_SYMBOL(secure_tcpv6_ts_off);
-u32 secure_tcpv6_seq_and_tsoff(const __be32 *saddr, const __be32 *daddr,
- __be16 sport, __be16 dport, u32 *tsoff)
+u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
+ __be16 sport, __be16 dport)
{
const struct {
struct in6_addr saddr;
@@ -78,14 +84,14 @@ u32 secure_tcpv6_seq_and_tsoff(const __be32 *saddr, const __be32 *daddr,
.sport = sport,
.dport = dport
};
- u64 hash;
+ u32 hash;
+
net_secret_init();
hash = siphash(&combined, offsetofend(typeof(combined), dport),
&net_secret);
- *tsoff = secure_tcpv6_ts_off(saddr, daddr);
return seq_scale(hash);
}
-EXPORT_SYMBOL(secure_tcpv6_seq_and_tsoff);
+EXPORT_SYMBOL(secure_tcpv6_seq);
u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
__be16 dport)
@@ -107,11 +113,12 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
#endif
#ifdef CONFIG_INET
-static u32 secure_tcp_ts_off(__be32 saddr, __be32 daddr)
+u32 secure_tcp_ts_off(__be32 saddr, __be32 daddr)
{
if (sysctl_tcp_timestamps != 1)
return 0;
+ ts_secret_init();
return siphash_2u32((__force u32)saddr, (__force u32)daddr,
&ts_secret);
}
@@ -121,15 +128,15 @@ static u32 secure_tcp_ts_off(__be32 saddr, __be32 daddr)
* it would be easy enough to have the former function use siphash_4u32, passing
* the arguments as separate u32.
*/
-u32 secure_tcp_seq_and_tsoff(__be32 saddr, __be32 daddr,
- __be16 sport, __be16 dport, u32 *tsoff)
+u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
+ __be16 sport, __be16 dport)
{
- u64 hash;
+ u32 hash;
+
net_secret_init();
hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,
(__force u32)sport << 16 | (__force u32)dport,
&net_secret);
- *tsoff = secure_tcp_ts_off(saddr, daddr);
return seq_scale(hash);
}