Re: [PATCH 0/2] driver core: platform: avoid use-after-free on device name

["Théo Lebrun" <theo.lebrun@bootlin.com>]

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#L1357

Regards,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com