linux-kernel - Re: [PATCH] ipv4: fib_rules: Fix possible infinite loop in fib_empty

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Date:   Sat, 29 Dec 2018 14:46:50 +0800
From:   YueHaibing <yuehaibing@...wei.com>
To:     David Miller <davem@...emloft.net>
CC:     <kuznet@....inr.ac.ru>, <yoshfuji@...ux-ipv6.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv4: fib_rules: Fix possible infinite loop in
 fib_empty_table


On 2018/12/29 13:15, David Miller wrote:
> From: YueHaibing <yuehaibing@...wei.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).
> 

Thanks, will do it in v2.

> 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) {
> 	...
> 	}
> 
> .
>