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Commit 95a22cae authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

tcp: randomize tcp timestamp offsets for each connection 



jiffies based timestamps allow for easy inference of number of devices
behind NAT translators and also makes tracking of hosts simpler.

commit ceaa1fef ("tcp: adding a per-socket timestamp offset")
added the main infrastructure that is needed for per-connection ts
randomization, in particular writing/reading the on-wire tcp header
format takes the offset into account so rest of stack can use normal
tcp_time_stamp (jiffies).

So only two items are left:
 - add a tsoffset for request sockets
 - extend the tcp isn generator to also return another 32bit number
   in addition to the ISN.

Re-use of ISN generator also means timestamps are still monotonically
increasing for same connection quadruple, i.e. PAWS will still work.

Includes fixes from Eric Dumazet.

Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7df5358d

include/linux/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -123,6 +123,7 @@ struct tcp_request_sock { 
	u32				txhash;

	u32				rcv_isn;

	u32				snt_isn;

	u32				ts_off;

	u32				last_oow_ack_time; /* last SYNACK */

	u32				rcv_nxt; /* the ack # by SYNACK. For

						  * FastOpen it's the seq#

include/net/secure_seq.h

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

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

			       __be16 dport);

__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

				 __be16 sport, __be16 dport);

__u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,

				   __be16 sport, __be16 dport);

u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

			       __be16 sport, __be16 dport, u32 *tsoff);

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

				 __be16 sport, __be16 dport, u32 *tsoff);

u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

				__be16 sport, __be16 dport);

u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,

include/net/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -1827,7 +1827,7 @@ struct tcp_request_sock_ops { 
	struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,

				       const struct request_sock *req,

				       bool *strict);

	__u32 (*init_seq)(const struct sk_buff *skb);

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

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

			   struct flowi *fl, struct request_sock *req,

			   struct tcp_fastopen_cookie *foc,

net/core/secure_seq.c

+6 −4
Original line number Diff line number Diff line
@@ -40,8 +40,8 @@ static u32 seq_scale(u32 seq) 
#endif



#if IS_ENABLED(CONFIG_IPV6)

__u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,

				   __be16 sport, __be16 dport)

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

				 __be16 sport, __be16 dport, u32 *tsoff)

{

	u32 secret[MD5_MESSAGE_BYTES / 4];

	u32 hash[MD5_DIGEST_WORDS];
@@ -58,6 +58,7 @@ __u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr, 


	md5_transform(hash, secret);



	*tsoff = hash[1];

	return seq_scale(hash[0]);

}

EXPORT_SYMBOL(secure_tcpv6_sequence_number);
@@ -86,8 +87,8 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral); 


#ifdef CONFIG_INET



__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

				 __be16 sport, __be16 dport)

u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

			       __be16 sport, __be16 dport, u32 *tsoff)

{

	u32 hash[MD5_DIGEST_WORDS];
@@ -99,6 +100,7 @@ __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr, 


	md5_transform(hash, net_secret);



	*tsoff = hash[1];

	return seq_scale(hash[0]);

}

net/ipv4/syncookies.c

+1 −0
Original line number Diff line number Diff line
@@ -334,6 +334,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) 
	treq = tcp_rsk(req);

	treq->rcv_isn		= ntohl(th->seq) - 1;

	treq->snt_isn		= cookie;

	treq->ts_off		= 0;

	req->mss		= mss;

	ireq->ir_num		= ntohs(th->dest);

	ireq->ir_rmt_port	= th->source;