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. 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]. [0]: https://elixir.bootlin.com/linux/v6.13.2/source/sound/soc/loongson/loongson_i2s_plat.c#L155 [1]: https://elixir.bootlin.com/linux/v6.13.2/source/drivers/base/platform.c#L581 [2]: https://elixir.bootlin.com/linux/v6.13.2/source/drivers/gpu/drm/drm_drv.c#L679 [3]: https://elixir.bootlin.com/linux/v6.13.2/source/include/linux/i2c.h#L343 [4]: https://elixir.bootlin.com/linux/v6.13.2/source/include/linux/pci.h#L2150 This can be reproduced using Buildroot's qemu_aarch64_virt_defconfig with CONFIG_KASAN=y and a dev_set_name() inside the probe of: drivers/pci/controller/pci-host-common.c The below splat appears at boot. It happens whenever something tries to access pdev->name; one big consumer of this field is platform_match() that fallbacks to name matching. ================================================================== BUG: KASAN: slab-use-after-free in strcmp+0x2c/0x78 Read of size 1 at addr ffffff80c0300160 by task swapper/0/1 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.6.32 #1 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x90/0xe8 show_stack+0x18/0x24 dump_stack_lvl+0x48/0x60 print_report+0xf8/0x5d8 kasan_report+0x90/0xcc __asan_load1+0x60/0x6c strcmp+0x2c/0x78 platform_match+0xd0/0x140 __driver_attach+0x44/0x240 bus_for_each_dev+0xe4/0x160 driver_attach+0x34/0x44 bus_add_driver+0x134/0x270 driver_register+0xa4/0x1e4 __platform_driver_register+0x44/0x54 ged_driver_init+0x1c/0x28 do_one_initcall+0xdc/0x260 kernel_init_freeable+0x314/0x448 kernel_init+0x2c/0x1e0 ret_from_fork+0x10/0x20 Allocated by task 1: kasan_save_stack+0x3c/0x64 kasan_set_track+0x2c/0x40 kasan_save_alloc_info+0x24/0x34 __kasan_kmalloc+0xb8/0xbc __kmalloc_node_track_caller+0x64/0xa4 kvasprintf+0xcc/0x16c kvasprintf_const+0xe8/0x180 kobject_set_name_vargs+0x54/0xd4 dev_set_name+0xa8/0xe4 of_device_make_bus_id+0x298/0x2b0 of_device_alloc+0x1ec/0x204 of_platform_device_create_pdata+0x60/0x168 of_platform_bus_create+0x20c/0x4a0 of_platform_populate+0x50/0x10c of_platform_default_populate_init+0xe0/0x100 do_one_initcall+0xdc/0x260 kernel_init_freeable+0x314/0x448 kernel_init+0x2c/0x1e0 ret_from_fork+0x10/0x20 Freed by task 1: kasan_save_stack+0x3c/0x64 kasan_set_track+0x2c/0x40 kasan_save_free_info+0x38/0x60 __kasan_slab_free+0xe4/0x150 __kmem_cache_free+0x134/0x26c kfree+0x54/0x6c kfree_const+0x34/0x40 kobject_set_name_vargs+0xa8/0xd4 dev_set_name+0xa8/0xe4 pci_host_common_probe+0x9c/0x294 platform_probe+0x90/0x100 really_probe+0x100/0x3cc __driver_probe_device+0xb8/0x18c driver_probe_device+0x108/0x1d8 __driver_attach+0xc8/0x240 bus_for_each_dev+0xe4/0x160 driver_attach+0x34/0x44 bus_add_driver+0x134/0x270 driver_register+0xa4/0x1e4 __platform_driver_register+0x44/0x54 gen_pci_driver_init+0x1c/0x28 do_one_initcall+0xdc/0x260 kernel_init_freeable+0x314/0x448 kernel_init+0x2c/0x1e0 ret_from_fork+0x10/0x20 The buggy address belongs to the object at ffffff80c0300160 which belongs to the cache kmalloc-16 of size 16 The buggy address is located 0 bytes inside of freed 16-byte region [ffffff80c0300160, ffffff80c0300170) The buggy address belongs to the physical page: page:0000000099fe29a0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x100300 flags: 0x8000000000000800(slab|zone=2) page_type: 0xffffffff() raw: 8000000000000800 ffffff80c00013c0 dead000000000122 0000000000000000 raw: 0000000000000000 0000000080800080 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffffff80c0300000: fa fb fc fc fa fb fc fc 00 07 fc fc 00 07 fc fc ffffff80c0300080: 00 07 fc fc 00 02 fc fc 00 02 fc fc 00 02 fc fc >ffffff80c0300100: 00 06 fc fc 00 06 fc fc 00 06 fc fc fa fb fc fc ^ ffffff80c0300180: 00 00 fc fc 00 00 fc fc 00 06 fc fc 00 06 fc fc ffffff80c0300200: 00 06 fc fc 00 06 fc fc 00 06 fc fc 00 06 fc fc ================================================================== Signed-off-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx> --- Théo Lebrun (2): driver core: platform: turn pdev->id_auto into pdev->flags driver core: platform: avoid use-after-free on pdev->name drivers/base/platform.c | 8 +++++--- drivers/of/platform.c | 12 +++++++++++- include/linux/platform_device.h | 4 +++- 3 files changed, 19 insertions(+), 5 deletions(-) --- base-commit: 0ad2507d5d93f39619fc42372c347d6006b64319 change-id: 20250217-pdev-uaf-1a779a98d81b Best regards, -- Théo Lebrun <theo.lebrun@xxxxxxxxxxx>
