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From: Damien Le Moal <Damien.LeMoal@wdc.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>,
	Jens Axboe <axboe@kernel.dk>,
	"linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [PATCH v7 01/11] libata: fix ata_host_alloc_pinfo()
Date: Mon, 16 Aug 2021 11:43:22 +0000	[thread overview]
Message-ID: <DM6PR04MB708163EABEE9CA6CAF62FAFFE7FD9@DM6PR04MB7081.namprd04.prod.outlook.com> (raw)
In-Reply-To: <ca7576c640d2c0bf2d80aef3098849d3c25311ff.camel@HansenPartnership.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

  reply	other threads:[~2021-08-16 11:43 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-16  1:44 [PATCH v7 00/11] libata cleanups and improvements Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 01/11] libata: fix ata_host_alloc_pinfo() Damien Le Moal
2021-08-16  5:53   ` Hannes Reinecke
2021-08-16 11:29   ` James Bottomley
2021-08-16 11:43     ` Damien Le Moal [this message]
2021-08-16  1:44 ` [PATCH v7 02/11] libata: fix ata_host_start() Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 03/11] libata: simplify ata_scsi_rbuf_fill() Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 04/11] libata: cleanup device sleep capability detection Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 05/11] libata: cleanup ata_dev_configure() Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 06/11] libata: cleanup NCQ priority handling Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 07/11] libata: fix ata_read_log_page() warning Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 08/11] libata: print feature list on device scan Damien Le Moal
2021-08-16  1:44 ` [PATCH v7 09/11] libata: Introduce ncq_prio_supported sysfs sttribute Damien Le Moal
2021-08-16  5:54   ` Hannes Reinecke
2021-08-16  1:44 ` [PATCH v7 10/11] docs: sysfs-block-device: improve ncq_prio_enable documentation Damien Le Moal
2021-08-16  5:54   ` Hannes Reinecke
2021-08-16  1:44 ` [PATCH v7 11/11] docs: sysfs-block-device: document ncq_prio_supported Damien Le Moal
2021-08-16  5:55   ` Hannes Reinecke
2021-08-18  9:54 ` [PATCH v7 00/11] libata cleanups and improvements Damien Le Moal
2021-08-18 13:20 ` Jens Axboe
2021-08-18 21:53   ` Damien Le Moal

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