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authorEric Dumazet <edumazet@google.com>2012-07-17 05:41:30 +0400
committerDavid S. Miller <davem@davemloft.net>2012-07-17 18:40:46 +0400
commit0c24604b68fc7810d429d6c3657b6f148270e528 (patch)
treef5dd9deb10cfbcf8742483ecda7d07899ccb57f9
parent5f3600ebe252aa5fe782e9f9115c66c639f62ac0 (diff)
downloadlinux-0c24604b68fc7810d429d6c3657b6f148270e528.tar.xz
tcp: implement RFC 5961 4.2
Implement the RFC 5691 mitigation against Blind Reset attack using SYN bit. Section 4.2 of RFC 5961 advises to send a Challenge ACK and drop incoming packet, instead of resetting the session. Add a new SNMP counter to count number of challenge acks sent in response to SYN packets. (netstat -s | grep TCPSYNChallenge) Remove obsolete TCPAbortOnSyn, since we no longer abort a TCP session because of a SYN flag. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Kiran Kumar Kella <kkiran@broadcom.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/snmp.h2
-rw-r--r--net/ipv4/proc.c2
-rw-r--r--net/ipv4/tcp_input.c32
3 files changed, 17 insertions, 19 deletions
diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index 673e0e928b2b..e5fcbd079e4a 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -208,7 +208,6 @@ enum
LINUX_MIB_TCPDSACKOFOSENT, /* TCPDSACKOfoSent */
LINUX_MIB_TCPDSACKRECV, /* TCPDSACKRecv */
LINUX_MIB_TCPDSACKOFORECV, /* TCPDSACKOfoRecv */
- LINUX_MIB_TCPABORTONSYN, /* TCPAbortOnSyn */
LINUX_MIB_TCPABORTONDATA, /* TCPAbortOnData */
LINUX_MIB_TCPABORTONCLOSE, /* TCPAbortOnClose */
LINUX_MIB_TCPABORTONMEMORY, /* TCPAbortOnMemory */
@@ -238,6 +237,7 @@ enum
LINUX_MIB_TCPOFODROP, /* TCPOFODrop */
LINUX_MIB_TCPOFOMERGE, /* TCPOFOMerge */
LINUX_MIB_TCPCHALLENGEACK, /* TCPChallengeACK */
+ LINUX_MIB_TCPSYNCHALLENGE, /* TCPSYNChallenge */
__LINUX_MIB_MAX
};
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 3e8e78f12a38..2a5240b2ea61 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -232,7 +232,6 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPDSACKOfoSent", LINUX_MIB_TCPDSACKOFOSENT),
SNMP_MIB_ITEM("TCPDSACKRecv", LINUX_MIB_TCPDSACKRECV),
SNMP_MIB_ITEM("TCPDSACKOfoRecv", LINUX_MIB_TCPDSACKOFORECV),
- SNMP_MIB_ITEM("TCPAbortOnSyn", LINUX_MIB_TCPABORTONSYN),
SNMP_MIB_ITEM("TCPAbortOnData", LINUX_MIB_TCPABORTONDATA),
SNMP_MIB_ITEM("TCPAbortOnClose", LINUX_MIB_TCPABORTONCLOSE),
SNMP_MIB_ITEM("TCPAbortOnMemory", LINUX_MIB_TCPABORTONMEMORY),
@@ -262,6 +261,7 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPOFODrop", LINUX_MIB_TCPOFODROP),
SNMP_MIB_ITEM("TCPOFOMerge", LINUX_MIB_TCPOFOMERGE),
SNMP_MIB_ITEM("TCPChallengeACK", LINUX_MIB_TCPCHALLENGEACK),
+ SNMP_MIB_ITEM("TCPSYNChallenge", LINUX_MIB_TCPSYNCHALLENGE),
SNMP_MIB_SENTINEL
};
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c841a8990377..8aaec5536111 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5270,8 +5270,8 @@ static void tcp_send_challenge_ack(struct sock *sk)
/* Does PAWS and seqno based validation of an incoming segment, flags will
* play significant role here.
*/
-static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
- const struct tcphdr *th, int syn_inerr)
+static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th, int syn_inerr)
{
const u8 *hash_location;
struct tcp_sock *tp = tcp_sk(sk);
@@ -5323,20 +5323,22 @@ static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
/* step 3: check security and precedence [ignored] */
- /* step 4: Check for a SYN in window. */
- if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+ /* step 4: Check for a SYN
+ * RFC 5691 4.2 : Send a challenge ack
+ */
+ if (th->syn) {
if (syn_inerr)
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
- NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
- tcp_reset(sk);
- return -1;
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
+ tcp_send_challenge_ack(sk);
+ goto discard;
}
- return 1;
+ return true;
discard:
__kfree_skb(skb);
- return 0;
+ return false;
}
/*
@@ -5366,7 +5368,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
const struct tcphdr *th, unsigned int len)
{
struct tcp_sock *tp = tcp_sk(sk);
- int res;
if (sk->sk_rx_dst) {
struct dst_entry *dst = sk->sk_rx_dst;
@@ -5555,9 +5556,8 @@ slow_path:
* Standard slow path.
*/
- res = tcp_validate_incoming(sk, skb, th, 1);
- if (res <= 0)
- return -res;
+ if (!tcp_validate_incoming(sk, skb, th, 1))
+ return 0;
step5:
if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
@@ -5877,7 +5877,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
int queued = 0;
- int res;
tp->rx_opt.saw_tstamp = 0;
@@ -5932,9 +5931,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
return 0;
}
- res = tcp_validate_incoming(sk, skb, th, 0);
- if (res <= 0)
- return -res;
+ if (!tcp_validate_incoming(sk, skb, th, 0))
+ return 0;
/* step 5: check the ACK field */
if (th->ack) {