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SubjectBUG: KASAN: i2c dev use after free
Hi,

When running a kernel (from todays next-20190304) that has
CONFIG_KASAN and CONFIG_DEBUG_KOBJECT_RELEASE enabled I run into this
call trace:

[ 494.752992][ C0]
==================================================================
[ 494.755726][ C0] BUG: KASAN: use-after-free in
collect_expired_timers+0x174/0x1d8
[ 494.758452][ C0] Write of size 8 at addr ffff800068868538 by
task swapper/0/0
[ 494.761000][ C0]
[ 494.761914][ C0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted
5.0.0-rc8-next-20190301-00013-g4c430594824f #1
[ 494.765290][ C0] Hardware name: linux,dummy-virt (DT)
[ 494.767168][ C0] Call trace:
[ 494.768358][ C0] dump_backtrace+0x0/0x280
[ 494.769970][ C0] show_stack+0x28/0x38
[ 494.771446][ C0] dump_stack+0x110/0x190
[ 494.772992][ C0] print_address_description+0x2cc/0x308
[ 494.774994][ C0] kasan_report+0x164/0x1b0
[ 494.776596][ C0] __asan_store8+0x94/0xa0
[ 494.778179][ C0] collect_expired_timers+0x174/0x1d8
[ 494.780059][ C0] run_timer_softirq+0x184/0x3f8
[ 494.781820][ C0] __do_softirq+0x54c/0xa58
[ 494.783408][ C0] irq_exit+0x150/0x1d0
[ 494.784892][ C0] __handle_domain_irq+0x114/0x158
[ 494.786709][ C0] gic_handle_irq+0x90/0xf8
[ 494.788293][ C0] el1_irq+0x100/0x200
[ 494.789768][ C0] arch_cpu_idle+0x270/0x4f0
[ 494.791398][ C0] default_idle_call+0x48/0x58
[ 494.793105][ C0] do_idle+0x264/0x3e0
[ 494.794568][ C0] cpu_startup_entry+0x2c/0x30
[ 494.796253][ C0] rest_init+0x458/0x46c
[ 494.797801][ C0] arch_call_rest_init+0x18/0x20
[ 494.799548][ C0] start_kernel+0x6f4/0x734
[ 494.801130][ C0]
[ 494.801989][ C0] Allocated by task 1:
[ 494.803453][ C0] __kasan_kmalloc.isra.0+0xbc/0x178
[ 494.805334][ C0] kasan_kmalloc+0xc/0x18
[ 494.806870][ C0] kmem_cache_alloc_trace+0x56c/0x5c8
[ 494.808752][ C0] i2cdev_attach_adapter+0xc0/0x2c8
[ 494.810612][ C0] i2cdev_notifier_call+0x5c/0x90
[ 494.812382][ C0] notifier_call_chain+0x108/0x1b0
[ 494.814214][ C0] __blocking_notifier_call_chain+0x7c/0xb0
[ 494.816271][ C0] blocking_notifier_call_chain+0x40/0x50
[ 494.818274][ C0] device_add+0x884/0xc00
[ 494.819820][ C0] device_register+0x2c/0x38
[ 494.821477][ C0] i2c_register_adapter+0x27c/0x6f0
[ 494.823295][ C0] i2c_add_adapter+0x110/0x130
[ 494.824980][ C0] i2c_add_numbered_adapter+0x48/0x78
[ 494.826899][ C0] unittest_i2c_bus_probe+0x1a8/0x1f4
[ 494.828778][ C0] platform_drv_probe+0xd8/0x1a8
[ 494.830741][ C0] really_probe+0x424/0x840
[ 494.832366][ C0] driver_probe_device+0x16c/0x238
[ 494.834216][ C0] device_driver_attach+0x90/0xc0
[ 494.835979][ C0] __driver_attach+0x1e8/0x200
[ 494.837697][ C0] bus_for_each_dev+0xf8/0x190
[ 494.839400][ C0] driver_attach+0x3c/0x48
[ 494.840986][ C0] bus_add_driver+0x20c/0x3d0
[ 494.842658][ C0] driver_register+0x168/0x200
[ 494.844369][ C0] __platform_driver_register+0x84/0x90
[ 494.846344][ C0] of_unittest_overlay+0x1444/0x14e8
[ 494.848200][ C0] of_unittest+0x2034/0x28a4
[ 494.849842][ C0] do_one_initcall+0x490/0x9bc
[ 494.851546][ C0] kernel_init_freeable+0xb94/0xcc0
[ 494.853398][ C0] kernel_init+0x1c/0x204
[ 494.854945][ C0] ret_from_fork+0x10/0x18
[ 494.856487][ C0]
[ 494.857356][ C0] Freed by task 1:
[ 494.858762][ C0] __kasan_slab_free+0x140/0x200
[ 494.860495][ C0] kasan_slab_free+0x10/0x18
[ 494.862116][ C0] kfree+0x3f4/0x608
[ 494.863457][ C0] put_i2c_dev+0xc8/0xd8
[ 494.864915][ C0] i2cdev_detach_adapter+0x70/0xd8
[ 494.866775][ C0] i2cdev_notifier_call+0x74/0x90
[ 494.868527][ C0] notifier_call_chain+0x108/0x1b0
[ 494.870292][ C0] __blocking_notifier_call_chain+0x7c/0xb0
[ 494.872204][ C0] blocking_notifier_call_chain+0x40/0x50
[ 494.874059][ C0] device_del+0x108/0x5b0
[ 494.875578][ C0] device_unregister+0x78/0x98
[ 494.877268][ C0] i2c_del_adapter+0x36c/0x3c8
[ 494.878820][ C0] unittest_i2c_bus_remove+0x88/0xa0
[ 494.880531][ C0] platform_drv_remove+0x44/0x70
[ 494.882211][ C0] really_probe+0x488/0x840
[ 494.883710][ C0] driver_probe_device+0x16c/0x238
[ 494.885514][ C0] device_driver_attach+0x90/0xc0
[ 494.887283][ C0] __driver_attach+0x1e8/0x200
[ 494.888910][ C0] bus_for_each_dev+0xf8/0x190
[ 494.890617][ C0] driver_attach+0x3c/0x48
[ 494.892179][ C0] bus_add_driver+0x20c/0x3d0
[ 494.893847][ C0] driver_register+0x168/0x200
[ 494.895489][ C0] __platform_driver_register+0x84/0x90
[ 494.897367][ C0] of_unittest_overlay+0x1444/0x14e8
[ 494.899235][ C0] of_unittest+0x2034/0x28a4
[ 494.900861][ C0] do_one_initcall+0x490/0x9bc
[ 494.902588][ C0] kernel_init_freeable+0xb94/0xcc0
[ 494.904429][ C0] kernel_init+0x1c/0x204
[ 494.905941][ C0] ret_from_fork+0x10/0x18
[ 494.907389][ C0]
[ 494.908198][ C0] The buggy address belongs to the object at
ffff800068868480
[ 494.908198][ C0] which belongs to the cache kmalloc-512 of size 512
[ 494.912942][ C0] The buggy address is located 184 bytes inside of
[ 494.912942][ C0] 512-byte region [ffff800068868480, ffff800068868680)
[ 494.917228][ C0] The buggy address belongs to the page:
[ 494.919084][ C0] page:ffff7e0001a21a00 count:1 mapcount:0
mapping:ffff80003fc0c980 index:0x0 compound_mapcount: 0
[ 494.922710][ C0] flags: 0xffff00000010200(slab|head)
[ 494.924623][ C0] raw: 0ffff00000010200 ffff7e0001a21608
ffff7e0001a22588 ffff80003fc0c980
[ 494.927501][ C0] raw: 0000000000000000 0000000000080008
00000001ffffffff 0000000000000000
[ 494.930369][ C0] page dumped because: kasan: bad access detected
[ 494.932528][ C0]
[ 494.933358][ C0] Memory state around the buggy address:
[ 494.935202][ C0] ffff800068868400: fc fc fc fc fc fc fc fc fc
fc fc fc fc fc fc fc
[ 494.937786][ C0] ffff800068868480: fb fb fb fb fb fb fb fb fb
fb fb fb fb fb fb fb
[ 494.940516][ C0] >ffff800068868500: fb fb fb fb fb fb fb fb fb
fb fb fb fb fb fb fb
[ 494.943241][ C0] ^
[ 494.945291][ C0] ffff800068868580: fb fb fb fb fb fb fb fb fb
fb fb fb fb fb fb fb
[ 494.948078][ C0] ffff800068868600: fb fb fb fb fb fb fb fb fb
fb fb fb fb fb fb fb
[ 494.950803][ C0]
==================================================================

I think patch introduced this issue d6760b14d4a1 ("i2c: dev: switch
from register_chrdev to cdev API")
and patch e6be18f6d62c ("i2c: dev: use after free in detach") tried to solve it.
However, when CONFIG_DEBUG_KOBJECT_RELEASE is enabled it delays
the ->release callback to make sure that anything that is done in release can
be done later than it happens in normal execution.
The cdev structure is supposed to be freed in the remove callback or after it,
but here it has already been freed by the put_i2c_dev().

Cheers,
Anders

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