Re: [PATCH] of: Deep-copy names of platform devices

From: Stepan Moskovchenko
Date: Tue Aug 12 2014 - 20:27:23 EST


On 8/12/2014 9:12 AM, Kumar Gala wrote:

On Aug 11, 2014, at 9:42 PM, Stepan Moskovchenko <stepanm@xxxxxxxxxxxxxx> wrote:

When we parse the device tree and allocate platform
devices, the 'name' of the newly-created platform_device
is set to point to the 'name' field of the 'struct device'
embedded within the platform_device. This is dangerous,
because the name of the 'struct device' is dynamically
allocated. Drivers may call dev_set_name() on the device,
which will free and reallocate the name of the device,
leaving the 'name' of the platform_device pointing to the
now-freed memory.

Furthermore, if the dev_set_name() call is made from a
driver's probe() function and a subsequent request results
in probe deferral, the dangling 'name' reference may lead
to the device being re-probed using the wrong driver.

To mitigate these scenarios, we use kstrdup to perform a
deep copy of the device name when assigning the name of the
platform_device, so that the platform_device name is
unaffected by any calls to dev_set_name() that might made
by drivers to rename the embedded 'struct device'.

Signed-off-by: Stepan Moskovchenko <stepanm@xxxxxxxxxxxxxx>
---
I suppose creating a 'pdev_set_name' API may seem like
another possibility, but I feel that dev.name and pdev.name
have two different meanings. One is used for device/driver
binding purposes, whereas the other serves a more general
identification purpose, and is used for things like sysfs.
Drivers might want to change dev.name while leaving the
pdev.name alone. I guess yet another possibility would be
to prohibit calling dev_set_name() on devices created from
device tree, but a driver does not necessarily know how a
given platform_device was allocated.

drivers/of/device.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index f685e55..fe5f025 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -54,7 +54,7 @@ int of_device_add(struct platform_device *ofdev)

/* name and id have to be set so that the platform bus doesn't get
* confused on matching */
- ofdev->name = dev_name(&ofdev->dev);
+ ofdev->name = kstrdup(dev_name(&ofdev->dev), GFP_KERNEL);
ofdev->id = -1;

/* device_add will assume that this device is on the same node as

Don’t we need to free this is of_device_unregister() now?

- k


Argh. I was confused by the asymmetric naming of the APIs, but after digging through the callers outside from drivers/of/, it looks like things do eventually filter down to of_device_add() in all the cases I could find. So yes, this does need to be fixed. Expect v2 soon.

Thanks
Steve

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