diff options
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 93 |
1 files changed, 68 insertions, 25 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index b76aa2d..56545b9 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -86,6 +86,9 @@ 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_challenge_ack_limit = 100; + int sysctl_tcp_stdurg __read_mostly; int sysctl_tcp_rfc1337 __read_mostly; int sysctl_tcp_max_orphans __read_mostly = NR_FILE; @@ -3633,6 +3636,24 @@ static int tcp_process_frto(struct sock *sk, int flag) return 0; } +/* RFC 5961 7 [ACK Throttling] */ +static void tcp_send_challenge_ack(struct sock *sk) +{ + /* unprotected vars, we dont care of overwrites */ + static u32 challenge_timestamp; + static unsigned int challenge_count; + u32 now = jiffies / HZ; + + if (now != challenge_timestamp) { + challenge_timestamp = now; + challenge_count = 0; + } + if (++challenge_count <= sysctl_tcp_challenge_ack_limit) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK); + tcp_send_ack(sk); + } +} + /* This routine deals with incoming acks, but not outgoing ones. */ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag) { @@ -3649,8 +3670,14 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag) /* If the ack is older than previous acks * then we can probably ignore it. */ - if (before(ack, prior_snd_una)) + if (before(ack, prior_snd_una)) { + /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */ + if (before(ack, prior_snd_una - tp->max_window)) { + tcp_send_challenge_ack(sk); + return -1; + } goto old_ack; + } /* If the ack includes data we haven't sent yet, discard * this segment (RFC793 Section 3.9). @@ -5168,8 +5195,8 @@ out: /* 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, - struct tcphdr *th, int syn_inerr) +static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, + struct tcphdr *th, int syn_inerr) { u8 *hash_location; struct tcp_sock *tp = tcp_sk(sk); @@ -5194,38 +5221,48 @@ static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, * an acknowledgment should be sent in reply (unless the RST * bit is set, if so drop the segment and return)". */ - if (!th->rst) + if (!th->rst) { + if (th->syn) + goto syn_challenge; tcp_send_dupack(sk, skb); + } goto discard; } /* 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; } - /* ts_recent update must be made after we are sure that the packet - * is in window. - */ - tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); - /* 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) { +syn_challenge: 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; } /* @@ -5255,7 +5292,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb, struct tcphdr *th, unsigned len) { struct tcp_sock *tp = tcp_sk(sk); - int res; /* * Header prediction. @@ -5435,14 +5471,18 @@ 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) goto discard; + /* ts_recent update must be made after we are sure that the packet + * is in window. + */ + tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); + tcp_rcv_rtt_measure_ts(sk, skb); /* Process urgent data. */ @@ -5747,7 +5787,6 @@ 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; @@ -5802,9 +5841,8 @@ 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) { @@ -5921,6 +5959,11 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, } else goto discard; + /* ts_recent update must be made after we are sure that the packet + * is in window. + */ + tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); + /* step 6: check the URG bit */ tcp_urg(sk, skb, th); |