Re: [PATCH v7 01/11] libata: fix ata_host_alloc_pinfo()

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2021/08/16 20:29, James Bottomley wrote:
> On Mon, 2021-08-16 at 10:44 +0900, Damien Le Moal wrote:
>> Avoid static checkers warnings about a potential NULL pointer
>> dereference for the port info variable pi. To do so, test that at
>> least
>> one port info is available on entry to ata_host_alloc_pinfo() and
>> start
>> the ata port initialization for() loop with pi initialized to the
>> first
>> port info passed as argument (which is already checked to be non
>> NULL).
>> Within the for() loop, get the next port info, if it is not NULL,
>> after initializing the ata port using the previous port info.
>>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>> ---
>>  drivers/ata/libata-core.c | 18 ++++++++++++++----
>>  1 file changed, 14 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
>> index 61c762961ca8..b237a718ea0f 100644
>> --- a/drivers/ata/libata-core.c
>> +++ b/drivers/ata/libata-core.c
>> @@ -5441,16 +5441,17 @@ struct ata_host *ata_host_alloc_pinfo(struct
>> device *dev,
>>  	struct ata_host *host;
>>  	int i, j;
>>  
>> +	/* We must have at least one port info */
>> +	if (!ppi[0])
>> +		return NULL;
> 
> I've got to ask why on this one: most libata drivers use a static array
> for the port info.  If the first element is NULL that's a coding
> failure inside the driver, so WARN_ON would probably be more helpful to
> the driver writer.
> 
> What makes the static checker think ppi isn't NULL?
> 
>> +
>>  	host = ata_host_alloc(dev, n_ports);
>>  	if (!host)
>>  		return NULL;
>>  
>> -	for (i = 0, j = 0, pi = NULL; i < host->n_ports; i++) {
>> +	for (i = 0, j = 0, pi = ppi[0]; i < host->n_ports; i++) {
>>  		struct ata_port *ap = host->ports[i];
>>  
>> -		if (ppi[j])
>> -			pi = ppi[j++];
>> -
>>  		ap->pio_mask = pi->pio_mask;
>>  		ap->mwdma_mask = pi->mwdma_mask;
>>  		ap->udma_mask = pi->udma_mask;
>> @@ -5460,6 +5461,15 @@ struct ata_host *ata_host_alloc_pinfo(struct
>> device *dev,
>>  
>>  		if (!host->ops && (pi->port_ops !=
>> &ata_dummy_port_ops))
>>  			host->ops = pi->port_ops;
>> +
>> +		/*
>> +		 * Check that the next port info is not NULL.
>> +		 * If it is, keep using the current one.
>> +		 */
>> +		if (j < n_ports - 1 && ppi[j + 1]) {
>> +			j++;
>> +			pi = ppi[j];
>> +		}
> 
> This looks completely pointless: once you've verified ppi[0] is not
> NULL above, there's no possible NULL deref in that loop and the static
> checker should see it.  If it doesn't we need a new static checker
> because we shouldn't be perturbing code for broken tools.

I do not know how to run that static checker which sent the warnings initially.
I changed the code to avoid all the "dumb" cases it thinks are possible and
leading to the NULL deref signaled.

I think we should drop this patch. If the checker complains again, then I can
revisit in a different series.

Jens, can you drop this one when you apply the series (if you think it is good
to apply). Or should I resend a v8 without this patch ?

> 
> James
> 
> 
> 


-- 
Damien Le Moal
Western Digital Research