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| author | Eric Dumazet <edumazet@google.com> | 2017-05-05 16:56:54 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-05-05 19:00:11 +0300 |
| commit | 84b114b98452c431299d99c135f751659e517acb (patch) | |
| tree | 53778bfd4964bed65ac40a9c1c57a73f21cb9664 /net/ipv4/syncookies.c | |
| parent | 9051247dcf9ecee156d2ddac39a4f1ca591f8428 (diff) | |
| download | linux-84b114b98452c431299d99c135f751659e517acb.tar.xz | |
tcp: randomize timestamps on syncookies
Whole point of randomization was to hide server uptime, but an attacker
can simply start a syn flood and TCP generates 'old style' timestamps,
directly revealing server jiffies value.
Also, TSval sent by the server to a particular remote address vary
depending on syncookies being sent or not, potentially triggering PAWS
drops for innocent clients.
Lets implement proper randomization, including for SYNcookies.
Also we do not need to export sysctl_tcp_timestamps, since it is not
used from a module.
In v2, I added Florian feedback and contribution, adding tsoff to
tcp_get_cookie_sock().
v3 removed one unused variable in tcp_v4_connect() as Florian spotted.
Fixes: 95a22caee396c ("tcp: randomize tcp timestamp offsets for each connection")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Tested-by: Florian Westphal <fw@strlen.de>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/syncookies.c')
| -rw-r--r-- | net/ipv4/syncookies.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 496b97e17aaf..0257d965f111 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -16,6 +16,7 @@ #include <linux/siphash.h> #include <linux/kernel.h> #include <linux/export.h> +#include <net/secure_seq.h> #include <net/tcp.h> #include <net/route.h> @@ -203,7 +204,7 @@ EXPORT_SYMBOL_GPL(__cookie_v4_check); struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, struct request_sock *req, - struct dst_entry *dst) + struct dst_entry *dst, u32 tsoff) { struct inet_connection_sock *icsk = inet_csk(sk); struct sock *child; @@ -213,6 +214,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, NULL, &own_req); if (child) { atomic_set(&req->rsk_refcnt, 1); + tcp_sk(child)->tsoffset = tsoff; sock_rps_save_rxhash(child, skb); inet_csk_reqsk_queue_add(sk, req, child); } else { @@ -292,6 +294,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) struct rtable *rt; __u8 rcv_wscale; struct flowi4 fl4; + u32 tsoff = 0; if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst) goto out; @@ -311,6 +314,11 @@ 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 (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { + tsoff = secure_tcp_ts_off(ip_hdr(skb)->daddr, ip_hdr(skb)->saddr); + tcp_opt.rcv_tsecr -= tsoff; + } + if (!cookie_timestamp_decode(&tcp_opt)) goto out; @@ -381,7 +389,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) ireq->rcv_wscale = rcv_wscale; ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst); - ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst); + ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst, tsoff); /* ip_queue_xmit() depends on our flow being setup * Normal sockets get it right from inet_csk_route_child_sock() */ |