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
