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Diffstat (limited to 'net/ipv4/syncookies.c')
-rw-r--r--net/ipv4/syncookies.c239
1 files changed, 122 insertions, 117 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 66fd80ef247..c86624b36a6 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -15,24 +15,17 @@
#include <linux/random.h>
#include <linux/cryptohash.h>
#include <linux/kernel.h>
+#include <linux/export.h>
#include <net/tcp.h>
#include <net/route.h>
-/* Timestamps: lowest 9 bits store TCP options */
-#define TSBITS 9
+/* Timestamps: lowest bits store TCP options */
+#define TSBITS 6
#define TSMASK (((__u32)1 << TSBITS) - 1)
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)
@@ -43,8 +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;
@@ -58,7 +54,7 @@ static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
/*
* 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
+ * tcp options in the lower 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.
@@ -70,11 +66,10 @@ __u32 cookie_init_timestamp(struct request_sock *req)
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;
+
+ options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
+ options |= ireq->sack_ok << 4;
+ options |= ireq->ecn_ok << 5;
ts = ts_now & ~TSMASK;
ts |= options;
@@ -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)
+ diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
+ if (diff >= MAX_SYNCOOKIE_AGE)
return (__u32)-1;
return (cookie -
@@ -138,72 +131,70 @@ static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
}
/*
- * This table has to be sorted and terminated with (__u16)-1.
- * XXX generate a better table.
- * Unresolved Issues: HIPPI with a 64k MSS is not well supported.
+ * 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%)
+ *
+ * 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 - 1,
- 256 - 1,
- 512 - 1,
- 536 - 1,
- 1024 - 1,
- 1440 - 1,
- 1460 - 1,
- 4312 - 1,
- (__u16)-1
+ 536,
+ 1300,
+ 1440, /* 1440, 1452: PPPoE */
+ 1460,
};
-/* The number doesn't include the -1 terminator */
-#define NUM_MSS (ARRAY_SIZE(msstab) - 1)
/*
* Generate a syncookie. mssp points to the mss, which is returned
* rounded down to the value encoded in the cookie.
*/
-__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
+u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
+ u16 *mssp)
{
- const struct iphdr *iph = ip_hdr(skb);
- const struct tcphdr *th = tcp_hdr(skb);
int mssind;
const __u16 mss = *mssp;
- tcp_synq_overflow(sk);
+ for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
+ if (mss >= msstab[mssind])
+ break;
+ *mssp = msstab[mssind];
- /* XXX sort msstab[] by probability? Binary search? */
- for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
- ;
- *mssp = msstab[mssind] + 1;
+ return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
+ th->source, th->dest, ntohl(th->seq),
+ mssind);
+}
+EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence);
+
+__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
+{
+ const struct iphdr *iph = ip_hdr(skb);
+ const struct tcphdr *th = tcp_hdr(skb);
+ tcp_synq_overflow(sk);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
- return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
- th->source, th->dest, ntohl(th->seq),
- jiffies / (HZ * 60), mssind);
+ return __cookie_v4_init_sequence(iph, th, 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.
*/
-static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
+int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
+ u32 cookie)
{
- const struct iphdr *iph = ip_hdr(skb);
- const struct tcphdr *th = tcp_hdr(skb);
__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 < NUM_MSS ? msstab[mssind] + 1 : 0;
+ return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
}
+EXPORT_SYMBOL_GPL(__cookie_v4_check);
static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
@@ -227,26 +218,39 @@ 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 are for snd_wscale
- * The next 4 lsb are for rcv_wscale
- * The next lsb is for sack_ok
+ * 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.
*/
-void cookie_check_timestamp(struct tcp_options_received *tcp_opt)
+bool cookie_check_timestamp(struct tcp_options_received *tcp_opt,
+ struct net *net, bool *ecn_ok)
{
- /* echoed timestamp, 9 lowest bits contain options */
+ /* echoed timestamp, 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;
+ if (!tcp_opt->saw_tstamp) {
+ tcp_clear_options(tcp_opt);
+ return true;
+ }
+
+ 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 >> 4) & 0x1;
+ if (tcp_opt->sack_ok && !sysctl_tcp_sack)
+ return false;
- if (tcp_opt->sack_ok)
- tcp_sack_reset(tcp_opt);
+ if ((options & 0xf) == 0xf)
+ return true; /* no window scaling */
- if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale)
- tcp_opt->wscale_ok = 1;
+ tcp_opt->wscale_ok = 1;
+ tcp_opt->snd_wscale = options & 0xf;
+ return sysctl_tcp_window_scaling != 0;
}
EXPORT_SYMBOL(cookie_check_timestamp);
@@ -254,7 +258,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
struct ip_options *opt)
{
struct tcp_options_received tcp_opt;
- u8 *hash_location;
struct inet_request_sock *ireq;
struct tcp_request_sock *treq;
struct tcp_sock *tp = tcp_sk(sk);
@@ -265,12 +268,14 @@ 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)
+ if (!sysctl_tcp_syncookies || !th->ack || th->rst)
goto out;
if (tcp_synq_no_recent_overflow(sk) ||
- (mss = cookie_check(skb, cookie)) == 0) {
+ (mss = __cookie_v4_check(ip_hdr(skb), th, cookie)) == 0) {
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
goto out;
}
@@ -279,10 +284,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
/* check for timestamp cookie support */
memset(&tcp_opt, 0, sizeof(tcp_opt));
- tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
+ tcp_parse_options(skb, &tcp_opt, 0, NULL);
- if (tcp_opt.saw_tstamp)
- cookie_check_timestamp(&tcp_opt);
+ if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok))
+ goto out;
ret = NULL;
req = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */
@@ -294,26 +299,28 @@ 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->ecn_ok = 0;
+ 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->ir_mark = inet_request_mark(sk, skb);
+ ireq->ecn_ok = ecn_ok;
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;
+ treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
+ treq->listener = NULL;
/* 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)
*/
if (opt && opt->optlen) {
- int opt_size = sizeof(struct ip_options) + opt->optlen;
+ int opt_size = sizeof(struct ip_options_rcu) + opt->optlen;
ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
- if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) {
+ if (ireq->opt != NULL && ip_options_echo(&ireq->opt->opt, skb)) {
kfree(ireq->opt);
ireq->opt = NULL;
}
@@ -325,7 +332,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
}
req->expires = 0UL;
- req->retrans = 0;
+ req->num_retrans = 0;
/*
* We need to lookup the route here to get at the correct
@@ -333,35 +340,33 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
* hasn't changed since we received the original syn, but I see
* no easy way to do this.
*/
- {
- struct flowi fl = { .mark = sk->sk_mark,
- .nl_u = { .ip4_u =
- { .daddr = ((opt && opt->srr) ?
- opt->faddr :
- ireq->rmt_addr),
- .saddr = ireq->loc_addr,
- .tos = RT_CONN_FLAGS(sk) } },
- .proto = IPPROTO_TCP,
- .flags = inet_sk_flowi_flags(sk),
- .uli_u = { .ports =
- { .sport = th->dest,
- .dport = th->source } } };
- security_req_classify_flow(req, &fl);
- if (ip_route_output_key(&init_net, &rt, &fl)) {
- reqsk_free(req);
- goto out;
- }
+ flowi4_init_output(&fl4, sk->sk_bound_dev_if, ireq->ir_mark,
+ RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
+ inet_sk_flowi_flags(sk),
+ (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)) {
+ reqsk_free(req);
+ goto out;
}
/* Try to redo what tcp_v4_send_synack did. */
- req->window_clamp = tp->window_clamp ? :dst_metric(&rt->u.dst, RTAX_WINDOW);
+ req->window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
tcp_select_initial_window(tcp_full_space(sk), req->mss,
&req->rcv_wnd, &req->window_clamp,
- ireq->wscale_ok, &rcv_wscale);
+ ireq->wscale_ok, &rcv_wscale,
+ dst_metric(&rt->dst, RTAX_INITRWND));
ireq->rcv_wscale = rcv_wscale;
- ret = get_cookie_sock(sk, skb, req, &rt->u.dst);
+ ret = get_cookie_sock(sk, skb, req, &rt->dst);
+ /* ip_queue_xmit() depends on our flow being setup
+ * Normal sockets get it right from inet_csk_route_child_sock()
+ */
+ if (ret)
+ inet_sk(ret)->cork.fl.u.ip4 = fl4;
out: return ret;
}
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2025-11-09 07:01:11 +0000