Hello Greg,
On Thu Feb 20, 2025 at 1:41 PM CET, Greg Kroah-Hartman wrote:
On Tue, Feb 18, 2025 at 12:00:11PM +0100, Théo Lebrun wrote:
The use-after-free bug appears when:
- A platform device is created from OF, by of_device_add();
- The same device's name is changed afterwards using dev_set_name(), by its probe for example.
Out of the 37 drivers that deal with platform devices and do a dev_set_name() call, only one might be affected. That driver is loongson-i2s-plat [0]. All other dev_set_name() calls are on children devices created on the spot. The issue was found on downstream kernels and we don't have what it takes to test loongson-i2s-plat.
Note: loongson-i2s-plat maintainers are CCed.
⟩ # Finding potential trouble-makers: ⟩ git grep -l 'struct platform_device' | xargs grep -l dev_set_name
The solution proposed is to add a flag to platform_device that tells if it is responsible for freeing its name. We can then duplicate the device name inside of_device_add() instead of copying the pointer.
Ick.
What is done elsewhere?
- Platform bus code does a copy of the argument name that is stored alongside the struct platform_device; see platform_device_alloc()[1].
- Other busses duplicate the device name; either through a dynamic allocation [2] or through an array embedded inside devices [3].
- Some busses don't have a separate name; when they want a name they take it from the device [4].
Really ick.
Let's do the right thing here and just get rid of the name pointer entirely in struct platform_device please. Isn't that the correct thing that way the driver core logic will work properly for all of this.
I would agree, if it wasn't for this consideration that is found in the commit message [0]:
It is important to duplicate! pdev->name must not change to make sure the platform_match() return value is stable over time. If we updated pdev->name alongside dev->name, once a device probes and changes its name then the platform_match() return value would change.
I'd be fine sending a V2 that removes the field *and the fallback* [1], but I don't have the full scope in mind to know what would become broken.
[0]: https://lore.kernel.org/lkml/20250218-pdev-uaf-v1-2-5ea1a0d3aba0@bootlin.com... [1]: https://elixir.bootlin.com/linux/v6.13.3/source/drivers/base/platform.c#L135...
Regards,
-- Théo Lebrun, Bootlin Embedded Linux and Kernel engineering https://bootlin.com