Re: [PATCH] ipv4: fib_rules: Fix possible infinite loop in fib_empty_table

[David Miller]

From: YueHaibing <yuehaib...@huawei.com>
Date: Wed, 26 Dec 2018 16:34:20 +0800

> diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
> index f8eb78d..1567e12 100644
> --- a/net/ipv4/fib_rules.c
> +++ b/net/ipv4/fib_rules.c
> @@ -200,9 +200,13 @@ static struct fib_table *fib_empty_table(struct net *net)
>  {
>       u32 id;
>  
> -     for (id = 1; id <= RT_TABLE_MAX; id++)
> +     for (id = 1; id <= RT_TABLE_MAX; id++) {
>               if (!fib_get_table(net, id))
>                       return fib_new_table(net, id);
> +
> +             if (id == RT_TABLE_MAX)
> +                     break;
> +     }
>       return NULL;
>  }

The loop now has two exit conditions, one of which (by your analysis
is completely impossible).

Please clean this up into a loop with better structure and no
impossible tests.  One approach could be simply:

        id = 1;
        while (1) {
        ...
                if (id++ == RT_TABLE_MAX)
                        break;
        }

Or even:

        id = 0;
        while (++id) {
        ...
        }