Re: [PATCH] PCI: Fix use-after-free in pci_bus_release_domain_nr()

[Sathyanarayanan Kuppuswamy]

On 3/29/23 8:59 AM, Rob Herring wrote:
> On Wed, Mar 29, 2023 at 10:13 AM Sathyanarayanan Kuppuswamy
> <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote:
>>
>>
>>
>> On 3/29/23 5:38 AM, Rob Herring wrote:
>>> Commit c14f7ccc9f5d ("PCI: Assign PCI domain IDs by ida_alloc()")
>>> introduced a use-after-free bug in the bus removal cleanup. The issue
>>> was found with kfence:
>>>
>>> [   19.285870] ==================================================================
>>> [   19.293351] BUG: KFENCE: use-after-free read in pci_bus_release_domain_nr+0x10/0x70
>>>
>>> [   19.302817] Use-after-free read at 0x000000007f3b80eb (in kfence-#115):
>>> [   19.309677]  pci_bus_release_domain_nr+0x10/0x70
>>> [   19.309691]  dw_pcie_host_deinit+0x28/0x78
>>> [   19.309702]  tegra_pcie_deinit_controller+0x1c/0x38 [pcie_tegra194]
>>> [   19.309734]  tegra_pcie_dw_probe+0x648/0xb28 [pcie_tegra194]
>>> [   19.309752]  platform_probe+0x90/0xd8
>>> [   19.309764]  really_probe+0xb8/0x298
>>> [   19.309777]  __driver_probe_device+0x78/0xd8
>>> [   19.309788]  driver_probe_device+0x38/0x120
>>> [   19.309799]  __device_attach_driver+0x94/0xe0
>>> [   19.309812]  bus_for_each_drv+0x70/0xc8
>>> [   19.309822]  __device_attach+0xfc/0x188
>>> [   19.309833]  device_initial_probe+0x10/0x18
>>> [   19.309844]  bus_probe_device+0x94/0xa0
>>> [   19.309854]  deferred_probe_work_func+0x80/0xb8
>>> [   19.309864]  process_one_work+0x1e0/0x348
>>> [   19.309882]  worker_thread+0x48/0x410
>>> [   19.309891]  kthread+0xf4/0x110
>>> [   19.309904]  ret_from_fork+0x10/0x20
>>>
>>> [   19.311457] kfence-#115: 0x00000000063a155a-0x00000000ba698da8, size=1072, cache=kmalloc-2k
>>>
>>> [   19.311469] allocated by task 96 on cpu 10 at 19.279323s:
>>> [   19.311562]  __kmem_cache_alloc_node+0x260/0x278
>>> [   19.311571]  kmalloc_trace+0x24/0x30
>>> [   19.311580]  pci_alloc_bus+0x24/0xa0
>>> [   19.311590]  pci_register_host_bridge+0x48/0x4b8
>>> [   19.311601]  pci_scan_root_bus_bridge+0xc0/0xe8
>>> [   19.311613]  pci_host_probe+0x18/0xc0
>>> [   19.311623]  dw_pcie_host_init+0x2c0/0x568
>>> [   19.311630]  tegra_pcie_dw_probe+0x610/0xb28 [pcie_tegra194]
>>> [   19.311647]  platform_probe+0x90/0xd8
>>> [   19.311653]  really_probe+0xb8/0x298
>>> [   19.311663]  __driver_probe_device+0x78/0xd8
>>> [   19.311672]  driver_probe_device+0x38/0x120
>>> [   19.311682]  __device_attach_driver+0x94/0xe0
>>> [   19.311694]  bus_for_each_drv+0x70/0xc8
>>> [   19.311702]  __device_attach+0xfc/0x188
>>> [   19.311713]  device_initial_probe+0x10/0x18
>>> [   19.311724]  bus_probe_device+0x94/0xa0
>>> [   19.311733]  deferred_probe_work_func+0x80/0xb8
>>> [   19.311743]  process_one_work+0x1e0/0x348
>>> [   19.311753]  worker_thread+0x48/0x410
>>> [   19.311763]  kthread+0xf4/0x110
>>> [   19.311771]  ret_from_fork+0x10/0x20
>>>
>>> [   19.311782] freed by task 96 on cpu 10 at 19.285833s:
>>> [   19.311799]  release_pcibus_dev+0x30/0x40
>>> [   19.311808]  device_release+0x30/0x90
>>> [   19.311814]  kobject_put+0xa8/0x120
>>> [   19.311832]  device_unregister+0x20/0x30
>>> [   19.311839]  pci_remove_bus+0x78/0x88
>>> [   19.311850]  pci_remove_root_bus+0x5c/0x98
>>> [   19.311860]  dw_pcie_host_deinit+0x28/0x78
>>> [   19.311866]  tegra_pcie_deinit_controller+0x1c/0x38 [pcie_tegra194]
>>> [   19.311883]  tegra_pcie_dw_probe+0x648/0xb28 [pcie_tegra194]
>>> [   19.311900]  platform_probe+0x90/0xd8
>>> [   19.311906]  really_probe+0xb8/0x298
>>> [   19.311916]  __driver_probe_device+0x78/0xd8
>>> [   19.311926]  driver_probe_device+0x38/0x120
>>> [   19.311936]  __device_attach_driver+0x94/0xe0
>>> [   19.311947]  bus_for_each_drv+0x70/0xc8
>>> [   19.311956]  __device_attach+0xfc/0x188
>>> [   19.311966]  device_initial_probe+0x10/0x18
>>> [   19.311976]  bus_probe_device+0x94/0xa0
>>> [   19.311985]  deferred_probe_work_func+0x80/0xb8
>>> [   19.311995]  process_one_work+0x1e0/0x348
>>> [   19.312005]  worker_thread+0x48/0x410
>>> [   19.312014]  kthread+0xf4/0x110
>>> [   19.312022]  ret_from_fork+0x10/0x20
>>>
>>> [   19.313579] CPU: 10 PID: 96 Comm: kworker/u24:2 Not tainted 6.2.0 #4
>>> [   19.320171] Hardware name:  /, BIOS 1.0-d7fb19b 08/10/2022
>>> [   19.325852] Workqueue: events_unbound deferred_probe_work_func
>>> [   19.331919] ==================================================================
>>>
>>> The stack trace is a bit misleading as dw_pcie_host_deinit() doesn't
>>> directly call pci_bus_release_domain_nr(). The issue turns out to be in
>>> pci_remove_root_bus() which first calls pci_remove_bus() which frees the
>>> struct pci_bus when its struct device is released. Then
>>> pci_bus_release_domain_nr() is called and accesses the freed
>>> struct pci_bus. Reordering these fixes the issue.
>>
>> Since time log is not useful, remove it and just add stack trace.
> 
> Actually, it was useful. It told me that the use-after-free happened
> pretty much right after the free.
> 
> Bjorn likes to edit commit messages so I'll leave it up to him to
> leave or change.
> 
>> Change looks good to me. But I am not sure whether pci_remove_bus()
>> directly frees struct pci_bus or just removes the bus resources?
> 
> struct pci_bus embeds a struct device. The struct device is put which
> causes the free of the struct pci_bus. So indirect in that the
> refcounting triggers the free, but direct in that pci_remove_bus()
> causes it.

Got it.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

> 
> Rob

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer