linux-kernel - Re: [PATCH] ata: pata_platform: Fix a NULL pointer dereference in __pata_platform

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Message-ID: <3621c7db-0b73-d7eb-f987-45ec59a6c738@opensource.wdc.com>
Date:   Fri, 28 Jan 2022 20:50:04 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Alexander Shiyan <shc_work@...l.ru>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jens Axboe <axboe@...nel.dk>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ata: pata_platform: Fix a NULL pointer dereference in
 __pata_platform_probe()

On 1/28/22 19:11, Greg KH wrote:
> On Tue, Jan 25, 2022 at 12:45:25AM +0800, Zhou Qingyang wrote:
>> In __pata_platform_probe(), devm_kzalloc() is assigned to ap->ops and
>> there is a dereference of it right after that, which could introduce a
>> NULL pointer dereference bug.
>>
>> Fix this by adding a NULL check of ap->ops.
>>
>> This bug was found by a static analyzer.
>>
>> Builds with 'make allyesconfig' show no new warnings,
>> and our static analyzer no longer warns about this code.
>>
>> Fixes: f3d5e4f18dba ("ata: pata_of_platform: Allow to use 16-bit wide data transfer")
>> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
>> ---
> 
> As stated in the past, please do not make contributions to the Linux
> kernel until umn.edu has properly resolved its development issues.

Aouch. My apologies. I forgot about this. Thank you for the reminder.

> 
>> The analysis employs differential checking to identify inconsistent 
>> security operations (e.g., checks or kfrees) between two code paths 
>> and confirms that the inconsistent operations are not recovered in the
>> current function or the callers, so they constitute bugs. 
>>
>> Note that, as a bug found by static analysis, it can be a false
>> positive or hard to trigger. Multiple researchers have cross-reviewed
>> the bug.
>>
>>  drivers/ata/pata_platform.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/ata/pata_platform.c b/drivers/ata/pata_platform.c
>> index 028329428b75..021ef9cbcbc1 100644
>> --- a/drivers/ata/pata_platform.c
>> +++ b/drivers/ata/pata_platform.c
>> @@ -128,6 +128,8 @@ int __pata_platform_probe(struct device *dev, struct resource *io_res,
>>  	ap = host->ports[0];
>>  
>>  	ap->ops = devm_kzalloc(dev, sizeof(*ap->ops), GFP_KERNEL);
>> +	if (ap->ops)
>> +		return -ENOMEM;
> 
> This change seems to leak memory.  Damien, please revert it.

I fixed the patch when applying, so there is no leak. This is a genuine
(potential) bug fix. Must I revert ? Is the "no contribution from
umn.edu" an unbreakable rule ?

> 
> thanks,
> 
> greg k-h


-- 
Damien Le Moal
Western Digital Research