Hi Maxime, On Tue, 22 Aug, 2023 11:12:28 +0200 Maxime Ripard <mripard@xxxxxxxxxx> wrote: > Hi, > > So, we discussed it this morning with Benjamin, and I think the culprit > is that the uclogic driver will allocate a char array with devm_kzalloc > in uclogic_input_configured() > (https://elixir.bootlin.com/linux/latest/source/drivers/hid/hid-uclogic-core.c#L149), > and will assign input_dev->name to that pointer. > > When the device is removed, the devm-allocated array is freed, and the > input framework will send a uevent in input_dev_uevent() using the > input_dev->name field: > > https://elixir.bootlin.com/linux/latest/source/drivers/input/input.c#L1688 > > So it's a classic dangling pointer situation. > > And even though it was revealed by that patch, I think the issue is > unrelated. The fundamental issue seems to be that the usage of devm in > that situation is wrong. > > input_dev->name is accessed by input_dev_uevent, which for KOBJ_UNBIND > and KOBJ_REMOVE will be called after remove. > > For example, in __device_release_driver() (with the driver remove hook > being called in device_remove() and devres_release_all() being called in > device_unbind_cleanup()): > https://elixir.bootlin.com/linux/latest/source/drivers/base/dd.c#L1278 > > So, it looks to me that, with or without the patch we merged recently, > the core has always sent uevent after device-managed resources were > freed. Thus, the uclogic (and any other input driver) was wrong in > allocating its input_dev name with devm_kzalloc (or the phys and uniq > fields in that struct). > > Note that freeing input_dev->name in remove would have been just as bad. > > Looking at the code quickly, at least hid-playstation, > hid-nvidia-shield, hid-logitech-hidpp, mms114 and tsc200x seem to be > affected by the same issue. I agree with this analysis overall. At least in hid-nvidia-shield, I can not use devm for allocating the input name string and explicitly free it after calling input_unregister_device. In this scenario, the name string would have been freed explicitly after input_put_device was called (since the input device is not devres managed). input_put_device would drop the reference count to zero and the device would be cleaned up at that point triggering KOBJ_REMOVE and firing off that final input_dev_uevent. I think this can be done for a number of the drivers as a workaround till this issue is properly resolved. If this seems appropriate, I can send out a series later in the day. This is just a workaround till the discussion below converges (which I am interested in). > > We discussed a couple of solutions with Benjamin, such as creating a > helper devm action to free and clear the input_dev->name field, droping > the name, phys and uniq fields from the uevent, or converting name, phys > and uniq to char arrays so drivers don't have to allocate them. > > We couldn't find a perfect one though, so... yeah. > > Maxime -- Thanks, Rahul Rameshbabu
