Re: [PATCH net] ipv6: make sure dev is not NULL before call ip6_frag_reasm

[Hangbin Liu]

On Mon, May 08, 2017 at 07:50:30AM -0700, Eric Dumazet wrote:
> On Mon, 2017-05-08 at 11:09 +0800, Hangbin Liu wrote:
> > Since ip6_frag_reasm() will call __in6_dev_get(dev), which will access
> > dev->ip6_ptr. We need to make sure dev is not NULL.
> > 
> > Signed-off-by: Hangbin Liu <liuhang...@gmail.com>
> > ---
> >  net/ipv6/reassembly.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
> > index e1da5b8..e3ebd62 100644
> > --- a/net/ipv6/reassembly.c
> > +++ b/net/ipv6/reassembly.c
> > @@ -348,7 +348,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct 
> > sk_buff *skb,
> >             fq->q.flags |= INET_FRAG_FIRST_IN;
> >     }
> >  
> > -   if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
> > +   if (dev && fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
> >         fq->q.meat == fq->q.len) {
> >             int res;
> >             unsigned long orefdst = skb->_skb_refdst;
> 
> 
> How dev could be possibly NULL here ?

I saw we checked the dev in this function

        dev = skb->dev;
        if (dev) {
                fq->iif = dev->ifindex;
                skb->dev = NULL;
        }

and upper caller ipv6_frag_rcv()

        fq = fq_find(net, fhdr->identification, &hdr->saddr, &hdr->daddr,
                     skb->dev ? skb->dev->ifindex : 0, ip6_frag_ecn(hdr));


Apologise that I did not do enough research to make sure whether skb->dev
could be NULL or not. I will do the check recently and reply when got a
confirmation.

Regards
Hangbin