netdev - Re: [PATCH net 3/6] ipv4: add check if nh_pcpu_rth

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Date:	Sun, 07 Oct 2012 15:34:23 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Julian Anastasov <ja@....bg>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net 3/6] ipv4: add check if nh_pcpu_rth_output is
 allocated

On Sun, 2012-10-07 at 14:26 +0300, Julian Anastasov wrote:
> 	Avoid NULL ptr dereference and caching if
> nh_pcpu_rth_output is not allocated.
> 
> Signed-off-by: Julian Anastasov <ja@....bg>
> ---
>  net/ipv4/route.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 488a8bb..0a600cc 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1798,18 +1798,24 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
>  	fnhe = NULL;
>  	if (fi) {
>  		struct rtable __rcu **prth;
> +		struct fib_nh *nh = &FIB_RES_NH(*res);
>  
> -		fnhe = find_exception(&FIB_RES_NH(*res), fl4->daddr);
> +		fnhe = find_exception(nh, fl4->daddr);
>  		if (fnhe)
>  			prth = &fnhe->fnhe_rth;
> -		else
> -			prth = __this_cpu_ptr(FIB_RES_NH(*res).nh_pcpu_rth_output);
> +		else {
> +			if (!nh->nh_pcpu_rth_output)
> +				goto add;
> +			prth = __this_cpu_ptr(nh->nh_pcpu_rth_output);
> +		}
>  		rth = rcu_dereference(*prth);
>  		if (rt_cache_valid(rth)) {
>  			dst_hold(&rth->dst);
>  			return rth;
>  		}
>  	}
> +
> +add:
>  	rth = rt_dst_alloc(dev_out,
>  			   IN_DEV_CONF_GET(in_dev, NOPOLICY),
>  			   IN_DEV_CONF_GET(in_dev, NOXFRM),

Alternative would be to make sure the allocation succeeded in
fib_create_info(), but I have no idea on the maximal number of fib_info
a complex routing setup might need ?

I guess a typical machine needs less than 30 fib_info...



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