linux-kernel - Re: [PATCH 7/10] cciss: use safer test on the result of find_first_zero

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Date:	Wed, 04 Jun 2014 10:55:53 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	scameron@...rdog.cce.hp.com, Julia Lawall <Julia.Lawall@...6.fr>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/10] cciss: use safer test on the result of find_first_zero_bit

On 06/04/2014 08:51 AM, scameron@...rdog.cce.hp.com wrote:
>> Find_first_zero_bit considers BITS_PER_LONG bits at a time, and thus may
>> return a larger number than the maximum position argument if that position
>> is not a multiple of BITS_PER_LONG.
>>
>> The semantic match that finds this problem is as follows:
>> (http://coccinelle.lip6.fr/)
>>
>> // <smpl>
>> @@
>> expression e1,e2,e3;
>> statement S1,S2;
>> @@
>>
>> e1 = find_first_zero_bit(e2,e3)
>> ...
>> if (e1 
>> - ==
>> + >=
>>   e3)
>> S1 else S2
>> // </smpl>
>>
>> Signed-off-by: Julia Lawall <Julia.Lawall@...6.fr>
>>
>> ---
>>  drivers/block/cciss.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff -u -p a/drivers/block/cciss.c b/drivers/block/cciss.c
>> --- a/drivers/block/cciss.c
>> +++ b/drivers/block/cciss.c
>> @@ -980,7 +980,7 @@ static CommandList_struct *cmd_alloc(ctl
>>  
>>  	do {
>>  		i = find_first_zero_bit(h->cmd_pool_bits, h->nr_cmds);
>> -		if (i == h->nr_cmds)
>> +		if (i >= h->nr_cmds)
>>  			return NULL;
>>  	} while (test_and_set_bit(i, h->cmd_pool_bits) != 0);
>>  	c = h->cmd_pool + i;
> 
> 
> Thanks. Ack.
> 
> You can add
> 
> Reviewed-by: Stephen M. Cameron <scameron@...rdog.cce.hp.com>
> 
> to this patch if you want.
> 
> You might consider adding "Cc: stable@...r.kernel.org" into the
> sign-off area as well.

There are two such instances in cciss.c, btw.

-- 
Jens Axboe

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