linux-kernel - Re: [PATCH v2] PCI: rework new_id interface for known vendor/device values

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Date:	Tue, 01 Apr 2014 18:00:08 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: rework new_id interface for known vendor/device values

Alex Williamson <alex.williamson@...hat.com> writes:

> On Tue, 2014-04-01 at 17:22 -0400, Bandan Das wrote:
>> While using the new_id interface, the user can unintentionally feed
>> incorrect values if the driver static table has a matching entry.
>> This is possible since only the device and vendor fields are
>> mandatory and the rest are optional. As a result, store_new_id
>> will fill in default values that are then passed on to the driver
>> and can have unintended consequences.
>> 
>> As an example, consider the ixgbe driver and the 82599EB network card :
>> echo "8086 10fb" > /sys/bus/pci/drivers/ixgbe/new_id
>> 
>> This will pass a driver_data value of 0 to the driver whereas
>> the index 0 in ixgbe actually points to a different set of card
>> operations.
>> 
>> This change returns an error if the user attempts to add a dynid for
>> a vendor/device combination for which a static entry already exists.
>> However, if the user intentionally wants a different set of values,
>> she must provide all the 7 fields and that will be accepted.
>> 
>> In KVM/device assignment scenario, the user might want 
>> to bind a device back to the host driver by writing to new_id
>> and trip on a possible null pointer dereference.
>> 
>> Signed-off-by: Bandan Das <bsd@...hat.com>
>> ---
>> v2:
>> 1. Return error if there is a matching static entry
>> and change commit message to reflect this behavior
>> 3. Fill in a pdev and call pci_match_id instead of creating
>> a new matching function
>> 4. Change commit message to reflect that libvirt does not
>> depend on this behavior
>> 
>>  drivers/pci/pci-driver.c | 23 ++++++++++++++++++++++-
>>  1 file changed, 22 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>> index 25f0bc6..493514e 100644
>> --- a/drivers/pci/pci-driver.c
>> +++ b/drivers/pci/pci-driver.c
>> @@ -103,11 +103,12 @@ store_new_id(struct device_driver *driver, const char *buf, size_t count)
>>  {
>>  	struct pci_driver *pdrv = to_pci_driver(driver);
>>  	const struct pci_device_id *ids = pdrv->id_table;
>> +	struct pci_dev *pdev;
>>  	__u32 vendor, device, subvendor=PCI_ANY_ID,
>>  		subdevice=PCI_ANY_ID, class=0, class_mask=0;
>>  	unsigned long driver_data=0;
>>  	int fields=0;
>> -	int retval;
>> +	int retval = 0;
>>  
>>  	fields = sscanf(buf, "%x %x %x %x %x %x %lx",
>>  			&vendor, &device, &subvendor, &subdevice,
>> @@ -115,6 +116,26 @@ store_new_id(struct device_driver *driver, const char *buf, size_t count)
>>  	if (fields < 2)
>>  		return -EINVAL;
>>  
>> +	if (fields != 7) {
>
> nit, pdev could be declared within this scope.

Ok, will spin a new one.

>> +		pdev = kzalloc(sizeof(*pdev), GFP_KERNEL);
>> +		if (!pdev)
>> +			return -ENOMEM;
>> +
>> +		pdev->vendor = vendor;
>> +		pdev->device = device;
>> +		pdev->subsystem_vendor = subvendor;
>> +		pdev->subsystem_device = subdevice;
>> +		pdev->class = class;
>
> Why not class_mask?
pdev->class_mask isn't used anywhere.

>> +
>> +		if (pci_match_id(pdrv->id_table, pdev))
>> +			retval = -EEXIST;
>> +
>> +		kfree(pdev);
>> +
>> +		if (retval)
>> +			return retval;
>> +	}
>> +
>>  	/* Only accept driver_data values that match an existing id_table
>>  	   entry */
>>  	if (ids) {
--
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