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Message-ID: <1342446411.23494.76.camel@edumazet-glaptop>
Date: Mon, 16 Jul 2012 15:46:51 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: "Kiran (Kiran Kumar) Kella" <kkiran@...adcom.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Is TCP vulneribility patch (as in RFC 5961) done in linux?
On Mon, 2012-07-16 at 10:33 +0200, Eric Dumazet wrote:
> On Mon, 2012-07-16 at 07:06 +0000, Kiran (Kiran Kumar) Kella wrote:
> > Looking into the file tcp_input.c in the latest stable linux release 3.4.4 source, I understand the fix for this recommendation is not implemented in Linux.
> > Any reason why it was not addressed?
>
> Nobody cared ?
>
> Are you planning to send a patch ?
>
Here is an RFC patch implementing RFC 5961 3.2
[PATCH net-next] tcp: implement RFC 5961 3.2
Implement the RFC 5691 mitigation against Blind
Reset attack using RST bit.
Add a new sysctl, tcp_challengeack_limit, to limit
number of challenge ACK sent per second.
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Kiran Kumar Kella <kkiran@...adcom.com>
---
Documentation/networking/ip-sysctl.txt | 5 +++
include/linux/snmp.h | 1
include/net/tcp.h | 1
net/ipv4/proc.c | 1
net/ipv4/sysctl_net_ipv4.c | 7 +++++
net/ipv4/tcp_input.c | 31 ++++++++++++++++++++++-
6 files changed, 45 insertions(+), 1 deletion(-)
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index e20c17a..f785fd1 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -565,6 +565,11 @@ tcp_limit_output_bytes - INTEGER
reduce the size of individual GSO packet (64KB being the max)
Default: 131072
+tcp_challengeack_limit - INTEGER
+ Limits number of Challenge ACK sent per second, as recommended
+ in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
+ Default: 100
+
UDP variables:
udp_mem - vector of 3 INTEGERs: min, pressure, max
diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index 2e68f5b..594638e 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -234,6 +234,7 @@ enum
LINUX_MIB_TCPREQQFULLDROP, /* TCPReqQFullDrop */
LINUX_MIB_TCPRETRANSFAIL, /* TCPRetransFail */
LINUX_MIB_TCPRCVCOALESCE, /* TCPRcvCoalesce */
+ LINUX_MIB_TCPCHALLENGEACK, /* TCPChallengeACK */
__LINUX_MIB_MAX
};
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 439984b..fc14419 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -254,6 +254,7 @@ extern int sysctl_tcp_thin_linear_timeouts;
extern int sysctl_tcp_thin_dupack;
extern int sysctl_tcp_early_retrans;
extern int sysctl_tcp_limit_output_bytes;
+extern int sysctl_tcp_challengeack_limit;
extern atomic_long_t tcp_memory_allocated;
extern struct percpu_counter tcp_sockets_allocated;
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 8af0d44..d589468 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -258,6 +258,7 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPReqQFullDrop", LINUX_MIB_TCPREQQFULLDROP),
SNMP_MIB_ITEM("TCPRetransFail", LINUX_MIB_TCPRETRANSFAIL),
SNMP_MIB_ITEM("TCPRcvCoalesce", LINUX_MIB_TCPRCVCOALESCE),
+ SNMP_MIB_ITEM("TCPChallengeACK", LINUX_MIB_TCPCHALLENGEACK),
SNMP_MIB_SENTINEL
};
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 70730f7..12df8e8 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -605,6 +605,13 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
+ {
+ .procname = "tcp_challengeack_limit",
+ .data = &sysctl_tcp_challengeack_limit,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
#ifdef CONFIG_NET_DMA
{
.procname = "tcp_dma_copybreak",
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 055ac49..8e7edff 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -88,6 +88,9 @@ int sysctl_tcp_app_win __read_mostly = 31;
int sysctl_tcp_adv_win_scale __read_mostly = 1;
EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
+/* rfc5961 challenge ack rate limiting */
+int sysctl_tcp_challengeack_limit = 100;
+
int sysctl_tcp_stdurg __read_mostly;
int sysctl_tcp_rfc1337 __read_mostly;
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
@@ -5244,6 +5247,23 @@ out:
}
#endif /* CONFIG_NET_DMA */
+static void tcp_send_challenge_ack(struct sock *sk)
+{
+ /* unprotected vars, we dont care of overwrites */
+ static u32 challenge_time;
+ static unsigned int challenge_count;
+ u32 now = tcp_time_stamp / HZ;
+
+ if (now != challenge_time) {
+ challenge_time = now;
+ challenge_count = 0;
+ }
+ if (++challenge_count <= sysctl_tcp_challengeack_limit) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
+ tcp_send_ack(sk);
+ }
+}
+
/* Does PAWS and seqno based validation of an incoming segment, flags will
* play significant role here.
*/
@@ -5280,7 +5300,16 @@ static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
/* Step 2: check RST bit */
if (th->rst) {
- tcp_reset(sk);
+ /* RFC 5961 3.2 :
+ * If sequence number exactly matches RCV.NXT, then
+ * RESET the connection
+ * else
+ * Send a challenge ACK
+ */
+ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
+ tcp_reset(sk);
+ else
+ tcp_send_challenge_ack(sk);
goto discard;
}
--
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