netdev - Re: [PATCH net V2] ip: frags: fix crash in ip_do

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Date:   Sun, 9 Sep 2018 11:24:12 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Taehee Yoo <ap420073@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Peter Oskolkov <posk@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net V2] ip: frags: fix crash in ip_do_fragment()

On Sun, Sep 9, 2018 at 10:47 AM Taehee Yoo <ap420073@...il.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 <edumazet@...gle.com>
> Signed-off-by: Taehee Yoo <ap420073@...il.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
>