Re: [PATCH v1] net/ipv4/nexthop: check the return value of nexthop_find_by_id()

[Li Zhong <floridsleeves@gmail.com>]

On Sat, Sep 17, 2022 at 7:46 AM David Ahern <dsahern@kernel.org> wrote:
>
> On 9/17/22 2:29 AM, Nikolay Aleksandrov wrote:
> > On 17/09/2022 05:30, Li Zhong wrote:
> >> Check the return value of nexthop_find_by_id(), which could be NULL on
> >> when not found. So we check to avoid null pointer dereference.
> >>
> >> Signed-off-by: Li Zhong <floridsleeves@gmail.com>
> >> ---
> >>  net/ipv4/nexthop.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> >> index 853a75a8fbaf..9f91bb78eed5 100644
> >> --- a/net/ipv4/nexthop.c
> >> +++ b/net/ipv4/nexthop.c
> >> @@ -2445,6 +2445,10 @@ static struct nexthop *nexthop_create_group(struct net *net,
> >>              struct nh_info *nhi;
> >>
> >>              nhe = nexthop_find_by_id(net, entry[i].id);
> >> +            if (!nhe) {
> >> +                    err = -EINVAL;
> >> +                    goto out_no_nh;
> >> +            }
> >>              if (!nexthop_get(nhe)) {
> >>                      err = -ENOENT;
> >>                      goto out_no_nh;
> >
> > These are validated in nh_check_attr_group() and should exist at this point.
> > Since remove_nexthop() should run under rtnl I don't see a way for a nexthop
> > to disappear after nh_check_attr_group() and before nexthop_create_group().
> >
>
> exactly. That lookup can't fail because the ids have been validated and
> all of this is under rtnl preventing nexthop removes.
>

Thanks for all your replies. That makes sense to me.