Commit 8c763681 authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

syncookies: check decoded options against sysctl settings 



Discard the ACK if we find options that do not match current sysctl
settings.

Previously it was possible to create a connection with sack, wscale,
etc. enabled even if the feature was disabled via sysctl.

Also remove an unneeded call to tcp_sack_reset() in
cookie_check_timestamp: Both call sites (cookie_v4_check,
cookie_v6_check) zero "struct tcp_options_received", hand it to
tcp_parse_options() (which does not change tcp_opt->num_sacks/dsack)
and then call cookie_check_timestamp().

Even if num_sacks/dsacks were changed, the structure is allocated on
the stack and after cookie_check_timestamp returns only a few selected
members are copied to the inet_request_sock.

Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 317fe0e6

include/net/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -464,7 +464,7 @@ extern __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, 
				     __u16 *mss);



extern __u32 cookie_init_timestamp(struct request_sock *req);

extern void cookie_check_timestamp(struct tcp_options_received *tcp_opt);

extern bool cookie_check_timestamp(struct tcp_options_received *tcp_opt);



/* From net/ipv6/syncookies.c */

extern struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);

net/ipv4/syncookies.c

+19 −6
Original line number Diff line number Diff line
@@ -230,23 +230,36 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, 
 * The lowest 4 bits are for snd_wscale

 * The next 4 lsb are for rcv_wscale

 * The next lsb is for sack_ok

 *

 * return false if we decode an option that should not be.

 */

void cookie_check_timestamp(struct tcp_options_received *tcp_opt)

bool cookie_check_timestamp(struct tcp_options_received *tcp_opt)

{

	/* echoed timestamp, 9 lowest bits contain options */

	u32 options = tcp_opt->rcv_tsecr & TSMASK;



	if (!tcp_opt->saw_tstamp)  {

		tcp_clear_options(tcp_opt);

		return true;

	}



	if (!sysctl_tcp_timestamps)

		return false;



	tcp_opt->snd_wscale = options & 0xf;

	options >>= 4;

	tcp_opt->rcv_wscale = options & 0xf;



	tcp_opt->sack_ok = (options >> 4) & 0x1;



	if (tcp_opt->sack_ok)

		tcp_sack_reset(tcp_opt);

	if (tcp_opt->sack_ok && !sysctl_tcp_sack)

		return false;



	if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale)

	if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale) {

		tcp_opt->wscale_ok = 1;

		return sysctl_tcp_window_scaling != 0;

	}

	return true;

}

EXPORT_SYMBOL(cookie_check_timestamp);
@@ -281,8 +294,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, 
	memset(&tcp_opt, 0, sizeof(tcp_opt));

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



	if (tcp_opt.saw_tstamp)

		cookie_check_timestamp(&tcp_opt);

	if (!cookie_check_timestamp(&tcp_opt))

		goto out;



	ret = NULL;

	req = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */

net/ipv6/syncookies.c

+2 −2
Original line number Diff line number Diff line
@@ -180,8 +180,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 
	memset(&tcp_opt, 0, sizeof(tcp_opt));

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



	if (tcp_opt.saw_tstamp)

		cookie_check_timestamp(&tcp_opt);

	if (!cookie_check_timestamp(&tcp_opt))

		goto out;



	ret = NULL;

	req = inet6_reqsk_alloc(&tcp6_request_sock_ops);

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