Commit 84b114b9 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: 95a22cae ("tcp: randomize tcp timestamp offsets for each connection")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarFlorian Westphal <fw@strlen.de>
Tested-by: default avatarFlorian Westphal <fw@strlen.de>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9051247d

include/net/secure_seq.h

+6 −4
Original line number Original line Diff line number Diff line
@@ -6,10 +6,12 @@ 
u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport);

u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport);

u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

			       __be16 dport);

			       __be16 dport);

u32 secure_tcp_seq_and_tsoff(__be32 saddr, __be32 daddr,

u32 secure_tcp_seq(__be32 saddr, __be32 daddr,

			     __be16 sport, __be16 dport, u32 *tsoff);

		   __be16 sport, __be16 dport);

u32 secure_tcpv6_seq_and_tsoff(const __be32 *saddr, const __be32 *daddr,

u32 secure_tcp_ts_off(__be32 saddr, __be32 daddr);

			       __be16 sport, __be16 dport, u32 *tsoff);

u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,

		     __be16 sport, __be16 dport);

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

u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

				__be16 sport, __be16 dport);

				__be16 sport, __be16 dport);

u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,

u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,

include/net/tcp.h

+3 −2
Original line number Original line Diff line number Diff line
@@ -470,7 +470,7 @@ void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb); 
/* From syncookies.c */

/* From syncookies.c */

struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,

struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,

				 struct request_sock *req,

				 struct request_sock *req,

				 struct dst_entry *dst);

				 struct dst_entry *dst, u32 tsoff);

int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,

int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,

		      u32 cookie);

		      u32 cookie);

struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);

struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
@@ -1822,7 +1822,8 @@ struct tcp_request_sock_ops { 
#endif

#endif

	struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,

	struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,

				       const struct request_sock *req);

				       const struct request_sock *req);

	__u32 (*init_seq_tsoff)(const struct sk_buff *skb, u32 *tsoff);

	u32 (*init_seq)(const struct sk_buff *skb);

	u32 (*init_ts_off)(const struct sk_buff *skb);

	int (*send_synack)(const struct sock *sk, struct dst_entry *dst,

	int (*send_synack)(const struct sock *sk, struct dst_entry *dst,

			   struct flowi *fl, struct request_sock *req,

			   struct flowi *fl, struct request_sock *req,

			   struct tcp_fastopen_cookie *foc,

			   struct tcp_fastopen_cookie *foc,

net/core/secure_seq.c

+19 −12
Original line number Original line Diff line number Diff line
@@ -24,9 +24,13 @@ static siphash_key_t ts_secret __read_mostly; 




static __always_inline void net_secret_init(void)

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));

	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

#endif





#ifdef CONFIG_INET

#ifdef CONFIG_INET
@@ -47,7 +51,7 @@ static u32 seq_scale(u32 seq) 
#endif

#endif





#if IS_ENABLED(CONFIG_IPV6)

#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 {

	const struct {

		struct in6_addr saddr;

		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)

	if (sysctl_tcp_timestamps != 1)

		return 0;

		return 0;





	ts_secret_init();

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

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

		       &ts_secret);

		       &ts_secret);

}

}

EXPORT_SYMBOL(secure_tcpv6_ts_off);





u32 secure_tcpv6_seq_and_tsoff(const __be32 *saddr, const __be32 *daddr,

u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,

			       __be16 sport, __be16 dport, u32 *tsoff)

		     __be16 sport, __be16 dport)

{

{

	const struct {

	const struct {

		struct in6_addr saddr;

		struct in6_addr saddr;
@@ -78,14 +84,14 @@ u32 secure_tcpv6_seq_and_tsoff(const __be32 *saddr, const __be32 *daddr, 
		.sport = sport,

		.sport = sport,

		.dport = dport

		.dport = dport

	};

	};

	u64 hash;

	u32 hash;



	net_secret_init();

	net_secret_init();

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

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

		       &net_secret);

		       &net_secret);

	*tsoff = secure_tcpv6_ts_off(saddr, daddr);

	return seq_scale(hash);

	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,

u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

			       __be16 dport)

			       __be16 dport)
@@ -107,11 +113,12 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral); 
#endif

#endif





#ifdef CONFIG_INET

#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)

	if (sysctl_tcp_timestamps != 1)

		return 0;

		return 0;





	ts_secret_init();

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

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

			    &ts_secret);

			    &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

 * it would be easy enough to have the former function use siphash_4u32, passing

 * the arguments as separate u32.

 * the arguments as separate u32.

 */

 */

u32 secure_tcp_seq_and_tsoff(__be32 saddr, __be32 daddr,

u32 secure_tcp_seq(__be32 saddr, __be32 daddr,

			     __be16 sport, __be16 dport, u32 *tsoff)

		   __be16 sport, __be16 dport)

{

{

	u64 hash;

	u32 hash;



	net_secret_init();

	net_secret_init();

	hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,

	hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,

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

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

			    &net_secret);

			    &net_secret);

	*tsoff = secure_tcp_ts_off(saddr, daddr);

	return seq_scale(hash);

	return seq_scale(hash);

}

}

net/ipv4/syncookies.c

+10 −2
Original line number Original line Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/siphash.h>

#include <linux/siphash.h>

#include <linux/kernel.h>

#include <linux/kernel.h>

#include <linux/export.h>

#include <linux/export.h>

#include <net/secure_seq.h>

#include <net/tcp.h>

#include <net/tcp.h>

#include <net/route.h>

#include <net/route.h>
@@ -203,7 +204,7 @@ EXPORT_SYMBOL_GPL(__cookie_v4_check); 




struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,

struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,

				 struct request_sock *req,

				 struct request_sock *req,

				 struct dst_entry *dst)

				 struct dst_entry *dst, u32 tsoff)

{

{

	struct inet_connection_sock *icsk = inet_csk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);

	struct sock *child;

	struct sock *child;
@@ -213,6 +214,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, 
						 NULL, &own_req);

						 NULL, &own_req);

	if (child) {

	if (child) {

		atomic_set(&req->rsk_refcnt, 1);

		atomic_set(&req->rsk_refcnt, 1);

		tcp_sk(child)->tsoffset = tsoff;

		sock_rps_save_rxhash(child, skb);

		sock_rps_save_rxhash(child, skb);

		inet_csk_reqsk_queue_add(sk, req, child);

		inet_csk_reqsk_queue_add(sk, req, child);

	} else {

	} else {
@@ -292,6 +294,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) 
	struct rtable *rt;

	struct rtable *rt;

	__u8 rcv_wscale;

	__u8 rcv_wscale;

	struct flowi4 fl4;

	struct flowi4 fl4;

	u32 tsoff = 0;





	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)

	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)

		goto out;

		goto out;
@@ -311,6 +314,11 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) 
	memset(&tcp_opt, 0, sizeof(tcp_opt));

	memset(&tcp_opt, 0, sizeof(tcp_opt));

	tcp_parse_options(skb, &tcp_opt, 0, NULL);

	tcp_parse_options(skb, &tcp_opt, 0, NULL);





	if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {

		tsoff = secure_tcp_ts_off(ip_hdr(skb)->daddr, ip_hdr(skb)->saddr);

		tcp_opt.rcv_tsecr -= tsoff;

	}



	if (!cookie_timestamp_decode(&tcp_opt))

	if (!cookie_timestamp_decode(&tcp_opt))

		goto out;

		goto out;
@@ -381,7 +389,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) 
	ireq->rcv_wscale  = rcv_wscale;

	ireq->rcv_wscale  = rcv_wscale;

	ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst);

	ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst);





	ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst);

	ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst, tsoff);

	/* ip_queue_xmit() depends on our flow being setup

	/* ip_queue_xmit() depends on our flow being setup

	 * Normal sockets get it right from inet_csk_route_child_sock()

	 * Normal sockets get it right from inet_csk_route_child_sock()

	 */

	 */

net/ipv4/tcp_input.c

+3 −5
Original line number Original line Diff line number Diff line
@@ -85,7 +85,6 @@ int sysctl_tcp_dsack __read_mostly = 1; 
int sysctl_tcp_app_win __read_mostly = 31;

int sysctl_tcp_app_win __read_mostly = 31;

int sysctl_tcp_adv_win_scale __read_mostly = 1;

int sysctl_tcp_adv_win_scale __read_mostly = 1;

EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);

EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);

EXPORT_SYMBOL(sysctl_tcp_timestamps);





/* rfc5961 challenge ack rate limiting */

/* rfc5961 challenge ack rate limiting */

int sysctl_tcp_challenge_ack_limit = 1000;

int sysctl_tcp_challenge_ack_limit = 1000;
@@ -6347,8 +6346,8 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, 
	if (security_inet_conn_request(sk, skb, req))

	if (security_inet_conn_request(sk, skb, req))

		goto drop_and_free;

		goto drop_and_free;





	if (isn && tmp_opt.tstamp_ok)

	if (tmp_opt.tstamp_ok)

		af_ops->init_seq_tsoff(skb, &tcp_rsk(req)->ts_off);

		tcp_rsk(req)->ts_off = af_ops->init_ts_off(skb);





	if (!want_cookie && !isn) {

	if (!want_cookie && !isn) {

		/* Kill the following clause, if you dislike this way. */

		/* Kill the following clause, if you dislike this way. */
@@ -6368,7 +6367,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, 
			goto drop_and_release;

			goto drop_and_release;

		}

		}





		isn = af_ops->init_seq_tsoff(skb, &tcp_rsk(req)->ts_off);

		isn = af_ops->init_seq(skb);

	}

	}

	if (!dst) {

	if (!dst) {

		dst = af_ops->route_req(sk, &fl, req);

		dst = af_ops->route_req(sk, &fl, req);
@@ -6380,7 +6379,6 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, 




	if (want_cookie) {

	if (want_cookie) {

		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);

		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);

		tcp_rsk(req)->ts_off = 0;

		req->cookie_ts = tmp_opt.tstamp_ok;

		req->cookie_ts = tmp_opt.tstamp_ok;

		if (!tmp_opt.tstamp_ok)

		if (!tmp_opt.tstamp_ok)

			inet_rsk(req)->ecn_ok = 0;

			inet_rsk(req)->ecn_ok = 0;

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