linux-kernel - Re: [PATCH v2 1/2] ip_tunnel: fix potential issue in ip_tunnel

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Date:   Wed, 7 Jun 2017 21:06:45 -0700
From:   Pravin Shelar <pshelar@....org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Haishuang Yan <yanhaishuang@...s.chinamobile.com>,
        "=David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Pravin B Shelar <pshelar@...ira.com>,
        Haishuang Yan <yanhaishuang@...s.chinamobile.com390e>
Subject: Re: [PATCH v2 1/2] ip_tunnel: fix potential issue in ip_tunnel_rcv

On Wed, Jun 7, 2017 at 8:15 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2017-06-07 at 19:13 -0700, Pravin Shelar wrote:
>> On Wed, Jun 7, 2017 at 5:57 PM, Haishuang Yan
>> <yanhaishuang@...s.chinamobile.com> wrote:
>> > When ip_tunnel_rcv fails, the tun_dst won't be freed, so move
>> > skb_dst_set to begin and tun_dst would be freed by kfree_skb.
>> >
>> > CC: Pravin B Shelar <pshelar@...ira.com>
>> > Fixes: 2e15ea390e6f ("ip_gre: Add support to collect tunnel metadata.")
>> > Signed-off-by: Haishuang Yan <yanhaishuang@...s.chinamobile.com390e>
>> > ---
>> >  net/ipv4/ip_tunnel.c | 6 +++---
>> >  1 file changed, 3 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
>> > index b878ecb..27fc20f 100644
>> > --- a/net/ipv4/ip_tunnel.c
>> > +++ b/net/ipv4/ip_tunnel.c
>> > @@ -386,6 +386,9 @@ int ip_tunnel_rcv(struct ip_tunnel *tunnel, struct sk_buff *skb,
>> >         const struct iphdr *iph = ip_hdr(skb);
>> >         int err;
>> >
>> > +       if (tun_dst)
>> > +               skb_dst_set(skb, (struct dst_entry *)tun_dst);
>> > +
>> If dst is set so early, skb_scrub_packet() would remove the tunnel dst
>> reference.
>> It is better to call skb_dst_drop() from error code path.
>
> Do we really want to keep a dst from another namespace if
> skb_scrub_packet() is called with xnet=true ?
>
tun_dst is allocated in same namespace. It is required for LWT to work.