linux-kernel - [PATCH] of: Deep-copy names of platform devices

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Message-Id: <1407891444-7311-1-git-send-email-stepanm@codeaurora.org>
Date:	Tue, 12 Aug 2014 17:57:24 -0700
From:	Stepan Moskovchenko <stepanm@...eaurora.org>
To:	grant.likely@...aro.org, robh+dt@...nel.org,
	devicetree@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	stepanm@...eaurora.org
Subject: [PATCH] of: Deep-copy names of platform devices

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@...eaurora.org>
---
This is technically a 'v2' patch, but it looks like I used
an old version of MAINTAINERS, so I'll just re-send this
as a new patch to avoid confusion for people who missed the
original.

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.

Steve

 drivers/of/device.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index f685e55..3e116f6 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
@@ -76,6 +76,7 @@ EXPORT_SYMBOL(of_device_register);
 void of_device_unregister(struct platform_device *ofdev)
 {
 	device_unregister(&ofdev->dev);
+	kfree(ofdev->name);
 }
 EXPORT_SYMBOL(of_device_unregister);

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