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Commit 28ee1b74 authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

secure_seq: downgrade to per-host timestamp offsets 



Unfortunately too many devices (not under our control) use tcp_tw_recycle=1,
which depends on timestamps being identical of the same saddr.

Although tcp_tw_recycle got removed in net-next we can't make
such end hosts disappear so downgrade to per-host timestamp offsets.

Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Reported-by: default avatarYvan Vanrossomme <yvan@vanrossomme.net>
Fixes: 95a22cae ("tcp: randomize tcp timestamp offsets for each connection")
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 95f25521

net/core/secure_seq.c

+29 −2
Original line number Diff line number Diff line
@@ -20,9 +20,11 @@ 
#include <net/tcp.h>



static siphash_key_t net_secret __read_mostly;

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));

}

#endif
@@ -45,6 +47,23 @@ static u32 seq_scale(u32 seq) 
#endif



#if IS_ENABLED(CONFIG_IPV6)

static u32 secure_tcpv6_ts_off(const __be32 *saddr, const __be32 *daddr)

{

	const struct {

		struct in6_addr saddr;

		struct in6_addr daddr;

	} __aligned(SIPHASH_ALIGNMENT) combined = {

		.saddr = *(struct in6_addr *)saddr,

		.daddr = *(struct in6_addr *)daddr,

	};



	if (sysctl_tcp_timestamps != 1)

		return 0;



	return siphash(&combined, offsetofend(typeof(combined), daddr),

		       &ts_secret);

}



u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,

				 __be16 sport, __be16 dport, u32 *tsoff)

{
@@ -63,7 +82,7 @@ u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr, 
	net_secret_init();

	hash = siphash(&combined, offsetofend(typeof(combined), dport),

		       &net_secret);

	*tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;

	*tsoff = secure_tcpv6_ts_off(saddr, daddr);

	return seq_scale(hash);

}

EXPORT_SYMBOL(secure_tcpv6_sequence_number);
@@ -88,6 +107,14 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral); 
#endif



#ifdef CONFIG_INET

static u32 secure_tcp_ts_off(__be32 saddr, __be32 daddr)

{

	if (sysctl_tcp_timestamps != 1)

		return 0;



	return siphash_2u32((__force u32)saddr, (__force u32)daddr,

			    &ts_secret);

}



/* secure_tcp_sequence_number(a, b, 0, d) == secure_ipv4_port_ephemeral(a, b, d),

 * but fortunately, `sport' cannot be 0 in any circumstances. If this changes,
@@ -103,7 +130,7 @@ u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr, 
	hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,

			    (__force u32)sport << 16 | (__force u32)dport,

			    &net_secret);

	*tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;

	*tsoff = secure_tcp_ts_off(saddr, daddr);

	return seq_scale(hash);

}