diff options
| -rw-r--r-- | net/ipv4/syncookies.c | 50 |
1 files changed, 35 insertions, 15 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 4ac7bcaf2f46..c3792c0557dd 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. */ bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, struct net *net, bool *ecn_ok) { /* 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); @@ -238,19 +257,20 @@ 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; + tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0; + *ecn_ok = options & TS_OPT_ECN; if (*ecn_ok && !net->ipv4.sysctl_tcp_ecn) return false; 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); |