linux-kernel - Re: [PATCH 1/2] regmap: fix NULL pointer dereference in regmap_name_read

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Message-ID: <65bf4e98-21c3-0d52-f25b-2ad78b4d0d06@lechnology.com>
Date:   Wed, 24 Jan 2018 10:24:46 -0600
From:   David Lechner <david@...hnology.com>
To:     Lars-Peter Clausen <lars@...afoo.de>, linux-kernel@...r.kernel.org
Cc:     Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/2] regmap: fix NULL pointer dereference in
 regmap_name_read_file()

On 01/24/2018 10:14 AM, Lars-Peter Clausen wrote:
> On 01/23/2018 11:53 PM, David Lechner wrote:
>> This fixes a possible NULL pointer dereference oops in
>> regmap_name_read_file() when the regmap does not have a device
>> associated with it.
>>
>> Signed-off-by: David Lechner <david@...hnology.com>
>> ---
>>   drivers/base/regmap/regmap-debugfs.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
>> index 36ce351..0df7379 100644
>> --- a/drivers/base/regmap/regmap-debugfs.c
>> +++ b/drivers/base/regmap/regmap-debugfs.c
>> @@ -40,6 +40,7 @@ static ssize_t regmap_name_read_file(struct file *file,
>>   				     loff_t *ppos)
>>   {
>>   	struct regmap *map = file->private_data;
>> +	const char *name = NULL;
>>   	int ret;
>>   	char *buf;
>>   
>> @@ -47,7 +48,10 @@ static ssize_t regmap_name_read_file(struct file *file,
>>   	if (!buf)
>>   		return -ENOMEM;
>>   
>> -	ret = snprintf(buf, PAGE_SIZE, "%s\n", map->dev->driver->name);
>> +	if (map->dev && map->dev->driver)
>> +		name = map->dev->driver->name;
>> +
>> +	ret = snprintf(buf, PAGE_SIZE, "%s\n", name);
> 
> Won't this print "(null)" now? Not sure if that is the best approach.
> 

The commit adding regmap_name_read_file() just says:

	regmap: Expose the driver name in debugfs

	Add a file called 'name' containing the name of the driver.

So, if a regmap doesn't have a driver, then "(null)" seems OK to me.
This is just for debugging anyway.