Subject: [24/33] ipv6: defrag: drop non-last frags smaller than min mtu

From: Florian Westphal <[email-masked]>
Date: Wed, 10 Oct 2018 12:30:10 -0700

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 <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Signed-off-by: Florian Westphal <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
[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 <[email-masked]>
---
 net/ipv6/netfilter/nf_conntrack_reasm.c | 4 ++++
 net/ipv6/reassembly.c                   | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index a39b5af43efe..cb72239dcff7 100644
--- 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(struct net *net, struct sk_buff *skb, u32 use
 	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);
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 32d4659d2d83..3cbcf099f6b2 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -515,6 +515,10 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
 		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) {