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authorFlorian Westphal <fw@strlen.de>2013-09-21 00:32:55 +0400
committerDavid S. Miller <davem@davemloft.net>2013-09-24 18:39:58 +0400
commit8c27bd75f04fb9cb70c69c3cfe24f4e6d8e15906 (patch)
tree28156d5d01cd4393da57eb328db87d784bdd4260 /net/ipv6/syncookies.c
parent61f860c356c3d15b6cf48ef35beea664921dec1e (diff)
downloadlinux-8c27bd75f04fb9cb70c69c3cfe24f4e6d8e15906.tar.xz
tcp: syncookies: reduce cookie lifetime to 128 seconds
We currently accept cookies that were created less than 4 minutes ago (ie, cookies with counter delta 0-3). Combined with the 8 mss table values, this yields 32 possible values (out of 2**32) that will be valid. Reducing the lifetime to < 2 minutes halves the guessing chance while still providing a large enough period. While at it, get rid of jiffies value -- they overflow too quickly on 32 bit platforms. getnstimeofday is used to create a counter that increments every 64s. perf shows getnstimeofday cost is negible compared to sha_transform; normal tcp initial sequence number generation uses getnstimeofday, too. Reported-by: Jakob Lell <jakob@jakoblell.com> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv6/syncookies.c')
-rw-r--r--net/ipv6/syncookies.c24
1 files changed, 7 insertions, 17 deletions
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index bf63ac8a49b9..13ca0a0ea680 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -36,14 +36,6 @@ static __u16 const msstab[] = {
9000 - 60,
};
-/*
- * 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
-
static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
struct dst_entry *dst)
@@ -86,8 +78,9 @@ static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *dadd
static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
const struct in6_addr *daddr,
__be16 sport, __be16 dport, __u32 sseq,
- __u32 count, __u32 data)
+ __u32 data)
{
+ 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)
@@ -96,15 +89,14 @@ static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
const struct in6_addr *daddr, __be16 sport,
- __be16 dport, __u32 sseq, __u32 count,
- __u32 maxdiff)
+ __be16 dport, __u32 sseq)
{
- __u32 diff;
+ __u32 diff, count = tcp_cookie_time();
cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
- if (diff >= maxdiff)
+ if (diff >= MAX_SYNCOOKIE_AGE)
return (__u32)-1;
return (cookie -
@@ -125,8 +117,7 @@ u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
*mssp = msstab[mssind];
return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
- th->dest, ntohl(th->seq),
- jiffies / (HZ * 60), mssind);
+ th->dest, ntohl(th->seq), mssind);
}
EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
@@ -146,8 +137,7 @@ int __cookie_v6_check(const struct ipv6hdr *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;
}