Re: [PATCH] [net/sched] Fix null pointer deref skb in tc_ctl_action

[Eric Dumazet <eric.dumazet@gmail.com>]

On 6/17/20 6:43 PM, Gaurav Singh wrote:
> Add null check for skb
> 

Bad choice really.

You have to really understand code intent before trying to fix it.

> Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
> ---
>  net/sched/act_api.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index 8ac7eb0a8309..fd584821d75a 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -1473,9 +1473,12 @@ static const struct nla_policy tcaa_policy[TCA_ROOT_MAX + 1] = {
>  static int tc_ctl_action(struct sk_buff *skb, struct nlmsghdr *n,
>  			 struct netlink_ext_ack *extack)
>  {
> +	if (!skb)
> +		return 0;


We do not allow this

warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]

> +
>  	struct net *net = sock_net(skb->sk);
>  	struct nlattr *tca[TCA_ROOT_MAX + 1];
> -	u32 portid = skb ? NETLINK_CB(skb).portid : 0;
> +	u32 portid = NETLINK_CB(skb).portid;
>  	int ret = 0, ovr = 0;
>  
>  	if ((n->nlmsg_type != RTM_GETACTION) &&
> 

Please compile your patches, do not expect us from doing this.