netdev - Re: [Patch net] fib: relax source validation check for loopback packets

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Date:   Sat, 13 Jul 2019 16:42:30 -0600
From:   David Ahern <dsahern@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     Julian Anastasov <ja@....bg>
Subject: Re: [Patch net] fib: relax source validation check for loopback
 packets

On 7/12/19 2:17 PM, Cong Wang wrote:
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 317339cd7f03..8662a44a28f9 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -388,6 +388,12 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
>  	fib_combine_itag(itag, &res);
>  
>  	dev_match = fib_info_nh_uses_dev(res.fi, dev);
> +	/* This is rare, loopback packets retain skb_dst so normally they
> +	 * would not even hit this slow path.
> +	 */
> +	dev_match = dev_match || (res.type == RTN_LOCAL &&
> +				  dev == net->loopback_dev &&

The dev should not be needed. res.type == RTN_LOCAL should be enough, no?

> +				  IN_DEV_ACCEPT_LOCAL(idev));

Why is this check needed? Can you give an example use that is fixed -
and add one to selftests/net/fib_tests.sh?


>  	if (dev_match) {
>  		ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_HOST;
>  		return ret;
>