Re: [PATCH stable 4.4 06/11] ipv6: defrag: drop non-last frags smaller than min mtu

[Greg KH <gregkh@linux-foundation.org>]

On Wed, Jan 23, 2019 at 10:19:41AM +0800, Mao Wenan wrote:
> From: Florian Westphal <fw@strlen.de>
> 
> [ Upstream commit 0ed4229b08c13c84a3c301a08defdc9e7f4467e6 ]
> 
> 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>
> ---
>  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 9cd8863..c5033a2 100644
> --- a/net/ipv6/netfilter/nf_conntrack_reasm.c
> +++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
> @@ -602,6 +602,10 @@ 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 (skb->len - skb_network_offset(skb) < IPV6_MIN_MTU &&
> +	    fhdr->frag_off & htons(IP6_MF))
> +		return -EINVAL;

This backport is incorrect, you should be returning a pointer, right?

How did you test this?  This should have blown up under test :(

I'm going to drop this whole series.  Please fix it up and test it
properly and then resend.

thanks,

greg k-h