Commit 1c449691 authored by Peter Oskolkov's avatar Peter Oskolkov Committed by Greg Kroah-Hartman
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ip: discard IPv4 datagrams with overlapping segments. 



This behavior is required in IPv6, and there is little need
to tolerate overlapping fragments in IPv4. This change
simplifies the code and eliminates potential DDoS attack vectors.

Tested: ran ip_defrag selftest (not yet available uptream).

Suggested-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarPeter Oskolkov <posk@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
Acked-by: default avatarStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
(cherry picked from commit 7969e5c4)
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5fff99e8

include/uapi/linux/snmp.h

+1 −0
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ enum 
	IPSTATS_MIB_ECT1PKTS,			/* InECT1Pkts */

	IPSTATS_MIB_ECT0PKTS,			/* InECT0Pkts */

	IPSTATS_MIB_CEPKTS,			/* InCEPkts */

	IPSTATS_MIB_REASM_OVERLAPS,		/* ReasmOverlaps */

	__IPSTATS_MIB_MAX

};

net/ipv4/ip_fragment.c

+19 −56
Original line number Diff line number Diff line
@@ -277,6 +277,7 @@ static int ip_frag_reinit(struct ipq *qp) 
/* Add new segment to existing queue. */

static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)

{

	struct net *net = container_of(qp->q.net, struct net, ipv4.frags);

	struct sk_buff *prev, *next;

	struct net_device *dev;

	unsigned int fragsize;
@@ -357,65 +358,23 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) 
	}



found:

	/* We found where to put this one.  Check for overlap with

	 * preceding fragment, and, if needed, align things so that

	 * any overlaps are eliminated.

	 */

	if (prev) {

		int i = (prev->ip_defrag_offset + prev->len) - offset;



		if (i > 0) {

			offset += i;

			err = -EINVAL;

			if (end <= offset)

				goto err;

			err = -ENOMEM;

			if (!pskb_pull(skb, i))

				goto err;

			if (skb->ip_summed != CHECKSUM_UNNECESSARY)

				skb->ip_summed = CHECKSUM_NONE;

		}

	}



	err = -ENOMEM;



	while (next && next->ip_defrag_offset < end) {

		int i = end - next->ip_defrag_offset; /* overlap is 'i' bytes */



		if (i < next->len) {

			int delta = -next->truesize;



			/* Eat head of the next overlapped fragment

			 * and leave the loop. The next ones cannot overlap.

			 */

			if (!pskb_pull(next, i))

				goto err;

			delta += next->truesize;

			if (delta)

				add_frag_mem_limit(qp->q.net, delta);

			next->ip_defrag_offset += i;

			qp->q.meat -= i;

			if (next->ip_summed != CHECKSUM_UNNECESSARY)

				next->ip_summed = CHECKSUM_NONE;

			break;

		} else {

			struct sk_buff *free_it = next;



			/* Old fragment is completely overridden with

			 * new one drop it.

	/* RFC5722, Section 4, amended by Errata ID : 3089

	 *                          When reassembling an IPv6 datagram, if

	 *   one or more its constituent fragments is determined to be an

	 *   overlapping fragment, the entire datagram (and any constituent

	 *   fragments) MUST be silently discarded.

	 *

	 * We do the same here for IPv4.

	 */

			next = next->next;



			if (prev)

				prev->next = next;

			else

				qp->q.fragments = next;

	/* Is there an overlap with the previous fragment? */

	if (prev &&

	    (prev->ip_defrag_offset + prev->len) > offset)

		goto discard_qp;



			qp->q.meat -= free_it->len;

			sub_frag_mem_limit(qp->q.net, free_it->truesize);

			kfree_skb(free_it);

		}

	}

	/* Is there an overlap with the next fragment? */

	if (next && next->ip_defrag_offset < end)

		goto discard_qp;



	/* Note : skb->ip_defrag_offset and skb->dev share the same location */

	dev = skb->dev;
@@ -463,6 +422,10 @@ found: 
	skb_dst_drop(skb);

	return -EINPROGRESS;



discard_qp:

	inet_frag_kill(&qp->q);

	err = -EINVAL;

	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);

err:

	kfree_skb(skb);

	return err;

net/ipv4/proc.c

+1 −0
Original line number Diff line number Diff line
@@ -132,6 +132,7 @@ static const struct snmp_mib snmp4_ipextstats_list[] = { 
	SNMP_MIB_ITEM("InECT1Pkts", IPSTATS_MIB_ECT1PKTS),

	SNMP_MIB_ITEM("InECT0Pkts", IPSTATS_MIB_ECT0PKTS),

	SNMP_MIB_ITEM("InCEPkts", IPSTATS_MIB_CEPKTS),

	SNMP_MIB_ITEM("ReasmOverlaps", IPSTATS_MIB_REASM_OVERLAPS),

	SNMP_MIB_SENTINEL

};