[PATCH stable 4.9 v2 22/29] ipv6: defrag: drop non-last frags smaller than min mtu

[Florian Fainelli]

From: Florian Westphal <f...@strlen.de>

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 <p...@google.com>
Cc: Eric Dumazet <eduma...@google.com>
Signed-off-by: Florian Westphal <f...@strlen.de>
Signed-off-by: David S. Miller <da...@davemloft.net>
(cherry picked from commit 0ed4229b08c13c84a3c301a08defdc9e7f4467e6)
---
 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 ff49d1f2c8cb..b81541701346 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -564,6 +564,10 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff 
*skb, u32 user)
        hdr = ipv6_hdr(skb);
        fhdr = (struct frag_hdr *)skb_transport_header(skb);
 
+       if (skb->len - skb_network_offset(skb) < IPV6_MIN_MTU &&
+           fhdr->frag_off & htons(IP6_MF))
+               return -EINVAL;
+
        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 dbe726c9a2ae..78656bbe50e7 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -516,6 +516,10 @@ 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) {
-- 
2.17.1