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syncookies: check decoded options against sysctl settings

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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: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2010-06-16 14:42:15 -07:00 committed by David S. Miller
parent 317fe0e6c5
commit 8c76368174
3 changed files with 22 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/tcp.h
View File

@ -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);

25
net/ipv4/syncookies.c
View File

@ -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 */

4
net/ipv6/syncookies.c
View File

@ -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);