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

[Rob Herring]

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.

Rob