Re: [PATCH] clk: fix slab-use-after-free when clk_core_populate_parent_map failed

[Brian Masney]

On Mon, Sep 29, 2025 at 04:31:19PM +0800, Yun Zhou wrote:
> If clk_core_populate_parent_map() fails, core->parents will be immediately
> released within clk_core_populate_parent_map(). Therefore it is can't be
> released in __clk_release() again.
> 
> This fixes the following KASAN reported issue:
> 
> ==================================================================
> BUG: KASAN: slab-use-after-free in __clk_release+0x80/0x160
> Read of size 8 at addr ffffff8043fd0980 by task kworker/u6:0/27
> 
> CPU: 1 PID: 27 Comm: kworker/u6:0 Tainted: G        W          6.6.69-yocto-standard+ #7
> Hardware name: Raspberry Pi 4 Model B (DT)
> Workqueue: events_unbound deferred_probe_work_func
> Call trace:
>  dump_backtrace+0x98/0xf8
>  show_stack+0x20/0x38
>  dump_stack_lvl+0x48/0x60
>  print_report+0xf8/0x5d8
>  kasan_report+0xb4/0x100
>  __asan_load8+0x9c/0xc0
>  __clk_release+0x80/0x160
>  __clk_register+0x6dc/0xfb8
>  devm_clk_hw_register+0x70/0x108
>  bcm2835_register_clock+0x284/0x358
>  bcm2835_clk_probe+0x2c4/0x438
>  platform_probe+0x98/0x110
>  really_probe+0x1e4/0x3e8
>  __driver_probe_device+0xc0/0x1a0
>  driver_probe_device+0x110/0x1e8
>  __device_attach_driver+0xf0/0x1a8
>  bus_for_each_drv+0xf8/0x178
>  __device_attach+0x120/0x240
>  device_initial_probe+0x1c/0x30
>  bus_probe_device+0xdc/0xe8
>  deferred_probe_work_func+0xe8/0x130
>  process_one_work+0x2a4/0x698
>  worker_thread+0x53c/0x708
>  kthread+0x1b4/0x1c8
>  ret_from_fork+0x10/0x20
> 
> Allocated by task 27:
>  kasan_save_stack+0x3c/0x68
>  kasan_set_track+0x2c/0x40
>  kasan_save_alloc_info+0x24/0x38
>  __kasan_kmalloc+0xd4/0xd8
>  __kmalloc+0x74/0x238
>  __clk_register+0x718/0xfb8
>  devm_clk_hw_register+0x70/0x108
>  bcm2835_register_clock+0x284/0x358
>  bcm2835_clk_probe+0x2c4/0x438
>  platform_probe+0x98/0x110
>  really_probe+0x1e4/0x3e8
>  __driver_probe_device+0xc0/0x1a0
>  driver_probe_device+0x110/0x1e8
>  __device_attach_driver+0xf0/0x1a8
>  bus_for_each_drv+0xf8/0x178
>  __device_attach+0x120/0x240
>  device_initial_probe+0x1c/0x30
>  bus_probe_device+0xdc/0xe8
>  deferred_probe_work_func+0xe8/0x130
>  process_one_work+0x2a4/0x698
>  worker_thread+0x53c/0x708
>  kthread+0x1b4/0x1c8
>  ret_from_fork+0x10/0x20
> 
> Freed by task 27:
>  kasan_save_stack+0x3c/0x68
>  kasan_set_track+0x2c/0x40
>  kasan_save_free_info+0x38/0x60
>  __kasan_slab_free+0x100/0x170
>  slab_free_freelist_hook+0xcc/0x218
>  __kmem_cache_free+0x158/0x210
>  kfree+0x88/0x140
>  __clk_register+0x9d0/0xfb8
>  devm_clk_hw_register+0x70/0x108
>  bcm2835_register_clock+0x284/0x358
>  bcm2835_clk_probe+0x2c4/0x438
>  platform_probe+0x98/0x110
>  really_probe+0x1e4/0x3e8
>  __driver_probe_device+0xc0/0x1a0
>  driver_probe_device+0x110/0x1e8
>  __device_attach_driver+0xf0/0x1a8
>  bus_for_each_drv+0xf8/0x178
>  __device_attach+0x120/0x240
>  device_initial_probe+0x1c/0x30
>  bus_probe_device+0xdc/0xe8
>  deferred_probe_work_func+0xe8/0x130
>  process_one_work+0x2a4/0x698
>  worker_thread+0x53c/0x708
>  kthread+0x1b4/0x1c8
>  ret_from_fork+0x10/0x20
> 
> The buggy address belongs to the object at ffffff8043fd0800
>  which belongs to the cache kmalloc-512 of size 512
> The buggy address is located 384 bytes inside of
>  freed 512-byte region [ffffff8043fd0800, ffffff8043fd0a00)
> 
> The buggy address belongs to the physical page:
> page:fffffffe010ff400 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffffff8043fd0e00 pfn:0x43fd0
> head:fffffffe010ff400 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0x4000000000000840(slab|head|zone=1)
> page_type: 0xffffffff()
> raw: 4000000000000840 ffffff8040002f40 ffffff8040000a50 ffffff8040000a50
> raw: ffffff8043fd0e00 0000000000150002 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffffff8043fd0880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffffff8043fd0900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffffff8043fd0980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                    ^
>  ffffff8043fd0a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffffff8043fd0a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
> 
> Fixes: 9d05ae531c2c ("clk: Initialize struct clk_core kref earlier")
> Signed-off-by: Yun Zhou <yun.zhou@xxxxxxxxxxxxx>

Is that the correct Fixes tag? What do you think about this instead?

Fixes: fc0c209c147f ("clk: Allow parents to be specified without string names")

Otherwise, the patch itself looks good to me.

Brian