On Sun, Sep 9, 2018 at 10:47 AM Taehee Yoo <ap420...@gmail.com> wrote:
>
> A kernel crash occurrs when defragmented packet is fragmented
> in ip_do_fragment().
> In defragment routine, skb_orphan() is called and
> skb->ip_defrag_offset is set. but skb->sk and
> skb->ip_defrag_offset are same union member. so that
> frag->sk is not NULL.
> Hence crash occurrs in skb->sk check routine in ip_do_fragment() when
> defragmented packet is fragmented.
>
> test commands:
> %iptables -t nat -I POSTROUTING -j MASQUERADE
> %hping3 192.168.4.2 -s 1000 -p 2000 -d 60000
>
> splat looks like:
>
> v2:
> - clear skb->sk at reassembly routine.(Eric Dumarzet)
>
> Fixes: fa0f527358bd ("ip: use rb trees for IP frag queue.")
> Suggested-by: Eric Dumazet <eduma...@google.com>
> Signed-off-by: Taehee Yoo <ap420...@gmail.com>
> ---
> net/ipv4/ip_fragment.c | 1 +
> net/ipv6/netfilter/nf_conntrack_reasm.c | 1 +
> 2 files changed, 2 insertions(+)
>
> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> index 88281fbce88c..e7227128df2c 100644
> --- a/net/ipv4/ip_fragment.c
> +++ b/net/ipv4/ip_fragment.c
> @@ -599,6 +599,7 @@ static int ip_frag_reasm(struct ipq *qp, struct sk_buff
> *skb,
> nextp = &fp->next;
> fp->prev = NULL;
> memset(&fp->rbnode, 0, sizeof(fp->rbnode));
> + fp->sk = NULL;
> head->data_len += fp->len;
> head->len += fp->len;
> if (head->ip_summed != fp->ip_summed)
> diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c
> b/net/ipv6/netfilter/nf_conntrack_reasm.c
> index 2a14d8b65924..8f68a518d9db 100644
> --- a/net/ipv6/netfilter/nf_conntrack_reasm.c
> +++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
> @@ -445,6 +445,7 @@ nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff
> *prev, struct net_devic
> else if (head->ip_summed == CHECKSUM_COMPLETE)
> head->csum = csum_add(head->csum, fp->csum);
> head->truesize += fp->truesize;
> + fp->sk = NULL;
This is not needed. IPv6 paths were not changed by recent commits.
> }
> sub_frag_mem_limit(fq->q.net, head->truesize);
>
> --
> 2.17.1
>
