On Thu Feb 20, 2025 at 3:06 PM CET, Greg Kroah-Hartman wrote: > On Thu, Feb 20, 2025 at 02:31:29PM +0100, Théo Lebrun wrote: >> 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 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]: > > What, that the of code is broken? Then it should be fixed, why does it > need a pointer to a name at all anyway? It shouldn't be needed there > either. I cannot guess why it originally has a separate pdev->name field. All I can tell you is a good reason to have one, as quoted below. >> > 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 > > The fallback will not need to be removed, properly point to the name of > the device and it should work correctly. No, it will not work correctly, as the above quote indicates. Let's assume we remove the field, this situation would be broken: - OF allocates platform devices and gives them names. - A device matches with a driver, which gets probed. - During the probe, driver does a dev_set_name(). - Afterwards, the upcoming platform_match() against other drivers are called with another device name. We should be safe as there are guardraids to not probe twice a device, see __driver_probe_device() that checks dev->driver is NULL. But it isn't a situation we should be in. Another broken situation: - OF allocates platform devices and gives them names. - A device matches with a driver, which gets probed based on its name. - During the probe, driver does a dev_set_name(). - Module is removed. - Module is re-added, the (driver, device) pair don't end up matching again because the device name changed. I might be missing other edge-cases. Conclusion: we need a constant name for platform devices as we want the return value of platform_match() to stay stable across time. Regards, -- Théo Lebrun, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
