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@xxxxxxxxxxx/ [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
