diff options
Diffstat (limited to 'net/ipv4/syncookies.c')
| -rw-r--r-- | net/ipv4/syncookies.c | 80 |
1 files changed, 32 insertions, 48 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 14a15c49129d..b95331e6c077 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -25,15 +25,7 @@ extern int sysctl_tcp_syncookies; -__u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; -EXPORT_SYMBOL(syncookie_secret); - -static __init int init_syncookies(void) -{ - get_random_bytes(syncookie_secret, sizeof(syncookie_secret)); - return 0; -} -__initcall(init_syncookies); +static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; #define COOKIEBITS 24 /* Upper bits store count */ #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) @@ -44,8 +36,11 @@ static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, u32 count, int c) { - __u32 *tmp = __get_cpu_var(ipv4_cookie_scratch); + __u32 *tmp; + + net_get_random_once(syncookie_secret, sizeof(syncookie_secret)); + tmp = __get_cpu_var(ipv4_cookie_scratch); memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c])); tmp[0] = (__force u32)saddr; tmp[1] = (__force u32)daddr; @@ -89,8 +84,7 @@ __u32 cookie_init_timestamp(struct request_sock *req) static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, - __be16 dport, __u32 sseq, __u32 count, - __u32 data) + __be16 dport, __u32 sseq, __u32 data) { /* * Compute the secure sequence number. @@ -102,7 +96,7 @@ static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, * As an extra hack, we add a small "data" value that encodes the * MSS into the second hash value. */ - + u32 count = tcp_cookie_time(); return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq + (count << COOKIEBITS) + ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) @@ -114,22 +108,21 @@ static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, * If the syncookie is bad, the data returned will be out of * range. This must be checked by the caller. * - * The count value used to generate the cookie must be within - * "maxdiff" if the current (passed-in) "count". The return value - * is (__u32)-1 if this test fails. + * The count value used to generate the cookie must be less than + * MAX_SYNCOOKIE_AGE minutes in the past. + * The return value (__u32)-1 if this test fails. */ static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr, - __be16 sport, __be16 dport, __u32 sseq, - __u32 count, __u32 maxdiff) + __be16 sport, __be16 dport, __u32 sseq) { - __u32 diff; + u32 diff, count = tcp_cookie_time(); /* Strip away the layers from the cookie */ cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */ diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS); - if (diff >= maxdiff) + if (diff >= MAX_SYNCOOKIE_AGE) return (__u32)-1; return (cookie - @@ -138,22 +131,22 @@ static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr, } /* - * MSS Values are taken from the 2009 paper - * 'Measuring TCP Maximum Segment Size' by S. Alcock and R. Nelson: - * - values 1440 to 1460 accounted for 80% of observed mss values - * - values outside the 536-1460 range are rare (<0.2%). + * MSS Values are chosen based on the 2011 paper + * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson. + * Values .. + * .. lower than 536 are rare (< 0.2%) + * .. between 537 and 1299 account for less than < 1.5% of observed values + * .. in the 1300-1349 range account for about 15 to 20% of observed mss values + * .. exceeding 1460 are very rare (< 0.04%) * - * Table must be sorted. + * 1460 is the single most frequently announced mss value (30 to 46% depending + * on monitor location). Table must be sorted. */ static __u16 const msstab[] = { - 64, - 512, 536, - 1024, - 1440, + 1300, + 1440, /* 1440, 1452: PPPoE */ 1460, - 4312, - 8960, }; /* @@ -173,7 +166,7 @@ u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th, return secure_tcp_syn_cookie(iph->saddr, iph->daddr, th->source, th->dest, ntohl(th->seq), - jiffies / (HZ * 60), mssind); + mssind); } EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence); @@ -189,13 +182,6 @@ __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) } /* - * This (misnamed) value is the age of syncookie which is permitted. - * Its ideal value should be dependent on TCP_TIMEOUT_INIT and - * sysctl_tcp_retries1. It's a rather complicated formula (exponential - * backoff) to compute at runtime so it's currently hardcoded here. - */ -#define COUNTER_TRIES 4 -/* * Check if a ack sequence number is a valid syncookie. * Return the decoded mss if it is, or 0 if not. */ @@ -204,9 +190,7 @@ int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th, { __u32 seq = ntohl(th->seq) - 1; __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr, - th->source, th->dest, seq, - jiffies / (HZ * 60), - COUNTER_TRIES); + th->source, th->dest, seq); return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; } @@ -315,10 +299,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, treq->rcv_isn = ntohl(th->seq) - 1; treq->snt_isn = cookie; req->mss = mss; - ireq->loc_port = th->dest; - ireq->rmt_port = th->source; - ireq->loc_addr = ip_hdr(skb)->daddr; - ireq->rmt_addr = ip_hdr(skb)->saddr; + ireq->ir_num = ntohs(th->dest); + ireq->ir_rmt_port = th->source; + ireq->ir_loc_addr = ip_hdr(skb)->daddr; + ireq->ir_rmt_addr = ip_hdr(skb)->saddr; ireq->ecn_ok = ecn_ok; ireq->snd_wscale = tcp_opt.snd_wscale; ireq->sack_ok = tcp_opt.sack_ok; @@ -358,8 +342,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, flowi4_init_output(&fl4, sk->sk_bound_dev_if, sk->sk_mark, RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP, inet_sk_flowi_flags(sk), - (opt && opt->srr) ? opt->faddr : ireq->rmt_addr, - ireq->loc_addr, th->source, th->dest); + (opt && opt->srr) ? opt->faddr : ireq->ir_rmt_addr, + ireq->ir_loc_addr, th->source, th->dest); security_req_classify_flow(req, flowi4_to_flowi(&fl4)); rt = ip_route_output_key(sock_net(sk), &fl4); if (IS_ERR(rt)) { |