linux-kernel - Re: [PATCH v1] net/ipv4/nexthop: check the return value of nexthop_find_by

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Date:   Sat, 17 Sep 2022 11:29:48 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Li Zhong <floridsleeves@...il.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     pabeni@...hat.com, kuba@...nel.org, edumazet@...gle.com,
        davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org
Subject: Re: [PATCH v1] net/ipv4/nexthop: check the return value of
 nexthop_find_by_id()

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@...il.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().

Did you notice a problem or have a stack dump?