Commit 354e4aa3 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation 



RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation]

  All TCP stacks MAY implement the following mitigation.  TCP stacks
  that implement this mitigation MUST add an additional input check to
  any incoming segment.  The ACK value is considered acceptable only if
  it is in the range of ((SND.UNA - MAX.SND.WND) <= SEG.ACK <=
  SND.NXT).  All incoming segments whose ACK value doesn't satisfy the
  above condition MUST be discarded and an ACK sent back.

Move tcp_send_challenge_ack() before tcp_ack() to avoid a forward
declaration.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Jerry Chu <hkchu@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 46baac38

net/ipv4/tcp_input.c

+25 −18
Original line number Diff line number Diff line
@@ -3552,6 +3552,24 @@ static bool tcp_process_frto(struct sock *sk, int flag) 
	return false;

}



/* 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, const struct sk_buff *skb, int flag)

{
@@ -3571,8 +3589,14 @@ static int tcp_ack(struct sock *sk, const 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).
@@ -5241,23 +5265,6 @@ out: 
}

#endif /* CONFIG_NET_DMA */



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);

	}

}



/* Does PAWS and seqno based validation of an incoming segment, flags will

 * play significant role here.

 */

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