diff options
Diffstat (limited to 'net/ipv4/syncookies.c')
| -rw-r--r-- | net/ipv4/syncookies.c | 89 |
1 files changed, 84 insertions, 5 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index abc752d45cf7..73ba98921d64 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -19,6 +19,10 @@ #include <linux/kernel.h> #include <net/tcp.h> +/* Timestamps: lowest 9 bits store TCP options */ +#define TSBITS 9 +#define TSMASK (((__u32)1 << TSBITS) - 1) + extern int sysctl_tcp_syncookies; __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; @@ -51,6 +55,39 @@ static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, return tmp[17]; } + +/* + * when syncookies are in effect and tcp timestamps are enabled we encode + * tcp options in the lowest 9 bits of the timestamp value that will be + * sent in the syn-ack. + * Since subsequent timestamps use the normal tcp_time_stamp value, we + * must make sure that the resulting initial timestamp is <= tcp_time_stamp. + */ +__u32 cookie_init_timestamp(struct request_sock *req) +{ + struct inet_request_sock *ireq; + u32 ts, ts_now = tcp_time_stamp; + u32 options = 0; + + ireq = inet_rsk(req); + if (ireq->wscale_ok) { + options = ireq->snd_wscale; + options |= ireq->rcv_wscale << 4; + } + options |= ireq->sack_ok << 8; + + ts = ts_now & ~TSMASK; + ts |= options; + if (ts > ts_now) { + ts >>= TSBITS; + ts--; + ts <<= TSBITS; + ts |= options; + } + return ts; +} + + static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, __u32 sseq, __u32 count, __u32 data) @@ -185,6 +222,35 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, return child; } + +/* + * when syncookies are in effect and tcp timestamps are enabled we stored + * additional tcp options in the timestamp. + * This extracts these options from the timestamp echo. + * + * The lowest 4 bits are for snd_wscale + * The next 4 lsb are for rcv_wscale + * The next lsb is for sack_ok + */ +void cookie_check_timestamp(struct tcp_options_received *tcp_opt) +{ + /* echoed timestamp, 9 lowest bits contain options */ + u32 options = tcp_opt->rcv_tsecr & TSMASK; + + 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->snd_wscale || tcp_opt->rcv_wscale) + tcp_opt->wscale_ok = 1; +} +EXPORT_SYMBOL(cookie_check_timestamp); + struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, struct ip_options *opt) { @@ -198,6 +264,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, int mss; struct rtable *rt; __u8 rcv_wscale; + struct tcp_options_received tcp_opt; if (!sysctl_tcp_syncookies || !th->ack) goto out; @@ -210,6 +277,13 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESRECV); + /* check for timestamp cookie support */ + memset(&tcp_opt, 0, sizeof(tcp_opt)); + tcp_parse_options(skb, &tcp_opt, 0); + + if (tcp_opt.saw_tstamp) + cookie_check_timestamp(&tcp_opt); + ret = NULL; req = reqsk_alloc(&tcp_request_sock_ops); /* for safety */ if (!req) @@ -228,6 +302,12 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, ireq->loc_addr = ip_hdr(skb)->daddr; ireq->rmt_addr = ip_hdr(skb)->saddr; ireq->opt = NULL; + ireq->snd_wscale = tcp_opt.snd_wscale; + ireq->rcv_wscale = tcp_opt.rcv_wscale; + ireq->sack_ok = tcp_opt.sack_ok; + ireq->wscale_ok = tcp_opt.wscale_ok; + ireq->tstamp_ok = tcp_opt.saw_tstamp; + req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; /* We throwed the options of the initial SYN away, so we hope * the ACK carries the same options again (see RFC1122 4.2.3.8) @@ -242,8 +322,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, } } - ireq->snd_wscale = ireq->rcv_wscale = ireq->tstamp_ok = 0; - ireq->wscale_ok = ireq->sack_ok = 0; req->expires = 0UL; req->retrans = 0; @@ -272,11 +350,12 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, } /* Try to redo what tcp_v4_send_synack did. */ - req->window_clamp = dst_metric(&rt->u.dst, RTAX_WINDOW); + req->window_clamp = tp->window_clamp ? :dst_metric(&rt->u.dst, RTAX_WINDOW); + tcp_select_initial_window(tcp_full_space(sk), req->mss, &req->rcv_wnd, &req->window_clamp, - 0, &rcv_wscale); - /* BTW win scale with syncookies is 0 by definition */ + ireq->wscale_ok, &rcv_wscale); + ireq->rcv_wscale = rcv_wscale; ret = get_cookie_sock(sk, skb, req, &rt->u.dst); |