diff options
Diffstat (limited to 'net/ipv4/syncookies.c')
| -rw-r--r-- | net/ipv4/syncookies.c | 86 |
1 files changed, 60 insertions, 26 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 32b98d0207b4..45fe60c5238e 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -19,10 +19,6 @@ #include <net/tcp.h> #include <net/route.h> -/* Timestamps: lowest bits store TCP options */ -#define TSBITS 6 -#define TSMASK (((__u32)1 << TSBITS) - 1) - extern int sysctl_tcp_syncookies; static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly; @@ -30,6 +26,30 @@ static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly; #define COOKIEBITS 24 /* Upper bits store count */ #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) +/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK + * stores TCP options: + * + * MSB LSB + * | 31 ... 6 | 5 | 4 | 3 2 1 0 | + * | Timestamp | ECN | SACK | WScale | + * + * When we receive a valid cookie-ACK, we look at the echoed tsval (if + * any) to figure out which TCP options we should use for the rebuilt + * connection. + * + * A WScale setting of '0xf' (which is an invalid scaling value) + * means that original syn did not include the TCP window scaling option. + */ +#define TS_OPT_WSCALE_MASK 0xf +#define TS_OPT_SACK BIT(4) +#define TS_OPT_ECN BIT(5) +/* There is no TS_OPT_TIMESTAMP: + * if ACK contains timestamp option, we already know it was + * requested/supported by the syn/synack exchange. + */ +#define TSBITS 6 +#define TSMASK (((__u32)1 << TSBITS) - 1) + static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv4_cookie_scratch); @@ -67,9 +87,11 @@ __u32 cookie_init_timestamp(struct request_sock *req) ireq = inet_rsk(req); - options = ireq->wscale_ok ? ireq->snd_wscale : 0xf; - options |= ireq->sack_ok << 4; - options |= ireq->ecn_ok << 5; + options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK; + if (ireq->sack_ok) + options |= TS_OPT_SACK; + if (ireq->ecn_ok) + options |= TS_OPT_ECN; ts = ts_now & ~TSMASK; ts |= options; @@ -219,16 +241,13 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, * additional tcp options in the timestamp. * This extracts these options from the timestamp echo. * - * The lowest 4 bits store snd_wscale. - * next 2 bits indicate SACK and ECN support. - * - * return false if we decode an option that should not be. + * return false if we decode a tcp option that is disabled + * on the host. */ -bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, - struct net *net, bool *ecn_ok) +bool cookie_timestamp_decode(struct tcp_options_received *tcp_opt) { /* echoed timestamp, lowest bits contain options */ - u32 options = tcp_opt->rcv_tsecr & TSMASK; + u32 options = tcp_opt->rcv_tsecr; if (!tcp_opt->saw_tstamp) { tcp_clear_options(tcp_opt); @@ -238,22 +257,35 @@ bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, if (!sysctl_tcp_timestamps) return false; - tcp_opt->sack_ok = (options & (1 << 4)) ? TCP_SACK_SEEN : 0; - *ecn_ok = (options >> 5) & 1; - if (*ecn_ok && !net->ipv4.sysctl_tcp_ecn) - return false; + tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0; if (tcp_opt->sack_ok && !sysctl_tcp_sack) return false; - if ((options & 0xf) == 0xf) + if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK) return true; /* no window scaling */ tcp_opt->wscale_ok = 1; - tcp_opt->snd_wscale = options & 0xf; + tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK; + return sysctl_tcp_window_scaling != 0; } -EXPORT_SYMBOL(cookie_check_timestamp); +EXPORT_SYMBOL(cookie_timestamp_decode); + +bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt, + const struct net *net, const struct dst_entry *dst) +{ + bool ecn_ok = tcp_opt->rcv_tsecr & TS_OPT_ECN; + + if (!ecn_ok) + return false; + + if (net->ipv4.sysctl_tcp_ecn) + return true; + + return dst_feature(dst, RTAX_FEATURE_ECN); +} +EXPORT_SYMBOL(cookie_ecn_ok); struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) { @@ -269,14 +301,16 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) int mss; struct rtable *rt; __u8 rcv_wscale; - bool ecn_ok = false; struct flowi4 fl4; if (!sysctl_tcp_syncookies || !th->ack || th->rst) goto out; - if (tcp_synq_no_recent_overflow(sk) || - (mss = __cookie_v4_check(ip_hdr(skb), th, cookie)) == 0) { + if (tcp_synq_no_recent_overflow(sk)) + goto out; + + mss = __cookie_v4_check(ip_hdr(skb), th, cookie); + if (mss == 0) { NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); goto out; } @@ -287,7 +321,7 @@ 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, 0, NULL); - if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok)) + if (!cookie_timestamp_decode(&tcp_opt)) goto out; ret = NULL; @@ -305,7 +339,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) ireq->ir_loc_addr = ip_hdr(skb)->daddr; ireq->ir_rmt_addr = ip_hdr(skb)->saddr; ireq->ir_mark = inet_request_mark(sk, skb); - ireq->ecn_ok = ecn_ok; ireq->snd_wscale = tcp_opt.snd_wscale; ireq->sack_ok = tcp_opt.sack_ok; ireq->wscale_ok = tcp_opt.wscale_ok; @@ -354,6 +387,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) dst_metric(&rt->dst, RTAX_INITRWND)); ireq->rcv_wscale = rcv_wscale; + ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst); ret = get_cookie_sock(sk, skb, req, &rt->dst); /* ip_queue_xmit() depends on our flow being setup |