[PATCH 4.4 24/34] ipv6: defrag: drop non-last frags smaller than min mtu - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Peter Oskolkov <posk@google.com>,
	Eric Dumazet <edumazet@google.com>,
	Florian Westphal <fw@strlen.de>,
	"David S. Miller" <davem@davemloft.net>,
	Mao Wenan <maowenan@huawei.com>,
	Ben Hutchings <ben.hutchings@codethink.co.uk>
Subject: [PATCH 4.4 24/34] ipv6: defrag: drop non-last frags smaller than min mtu
Date: Thu,  7 Feb 2019 12:42:06 +0100	[thread overview]
Message-ID: <20190207113026.506757266@linuxfoundation.org> (raw)
In-Reply-To: <20190207113025.552605181@linuxfoundation.org>

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@strlen.de>

commit 0ed4229b08c13c84a3c301a08defdc9e7f4467e6 upstream.

don't bother with pathological cases, they only waste cycles.
IPv6 requires a minimum MTU of 1280 so we should never see fragments
smaller than this (except last frag).

v3: don't use awkward "-offset + len"
v2: drop IPv4 part, which added same check w. IPV4_MIN_MTU (68).
    There were concerns that there could be even smaller frags
    generated by intermediate nodes, e.g. on radio networks.

Cc: Peter Oskolkov <posk@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Mao Wenan <maowenan@huawei.com>
[bwh: Backported to 4.4: In nf_ct_frag6_gather() use clone instead of skb,
 and goto ret_orig in case of error]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/netfilter/nf_conntrack_reasm.c |    4 ++++
 net/ipv6/reassembly.c                   |    4 ++++
 2 files changed, 8 insertions(+)

--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -574,6 +574,10 @@ struct sk_buff *nf_ct_frag6_gather(struc
 	hdr = ipv6_hdr(clone);
 	fhdr = (struct frag_hdr *)skb_transport_header(clone);
 
+	if (clone->len - skb_network_offset(clone) < IPV6_MIN_MTU &&
+	    fhdr->frag_off & htons(IP6_MF))
+		goto ret_orig;
+
 	skb_orphan(skb);
 	fq = fq_find(net, fhdr->identification, user, hdr,
 		     skb->dev ? skb->dev->ifindex : 0);
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -515,6 +515,10 @@ static int ipv6_frag_rcv(struct sk_buff
 		return 1;
 	}
 
+	if (skb->len - skb_network_offset(skb) < IPV6_MIN_MTU &&
+	    fhdr->frag_off & htons(IP6_MF))
+		goto fail_hdr;
+
 	iif = skb->dev ? skb->dev->ifindex : 0;
 	fq = fq_find(net, fhdr->identification, hdr, iif);
 	if (fq) {


