Messages in this thread |  | | Subject | Re: [PATCH] xhci-mtk: Fix NULL pointer dereference with xhci_irq() for shared_hcd | From | Mathias Nyman <> | Date | Tue, 4 Feb 2020 11:44:29 +0200 |
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On 1.2.2020 13.20, Macpaul Lin wrote: > On Fri, 2020-01-31 at 16:50 +0200, Mathias Nyman wrote: >> On 17.1.2020 9.41, Macpaul Lin wrote: >>> According to NULL pointer fix: https://tinyurl.com/uqft5ra >>> xhci: Fix NULL pointer dereference with xhci_irq() for shared_hcd >>> The similar issue has also been found in QC activities in Mediatek. >>> >>> Here quote the description from the referenced patch as follows. >>> "Commit ("f068090426ea xhci: Fix leaking USB3 shared_hcd >>> at xhci removal") sets xhci_shared_hcd to NULL without >>> stopping xhci host. This results into a race condition >>> where shared_hcd (super speed roothub) related interrupts >>> are being handled with xhci_irq happens when the >>> xhci_plat_remove is called and shared_hcd is set to NULL. >>> Fix this by setting the shared_hcd to NULL only after the >>> controller is halted and no interrupts are generated." >>> >>> Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org> >>> Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com> >>> --- >>> drivers/usb/host/xhci-mtk.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/usb/host/xhci-mtk.c b/drivers/usb/host/xhci-mtk.c >>> index b18a6baef204..c227c67f5dc5 100644 >>> --- a/drivers/usb/host/xhci-mtk.c >>> +++ b/drivers/usb/host/xhci-mtk.c >>> @@ -593,11 +593,11 @@ static int xhci_mtk_remove(struct platform_device *dev) >>> struct usb_hcd *shared_hcd = xhci->shared_hcd; >>> >>> usb_remove_hcd(shared_hcd); >>> - xhci->shared_hcd = NULL; >>> device_init_wakeup(&dev->dev, false); >>> >>> usb_remove_hcd(hcd); >>> usb_put_hcd(shared_hcd); >>> + xhci->shared_hcd = NULL; >>> usb_put_hcd(hcd); >>> xhci_mtk_sch_exit(mtk); >>> xhci_mtk_clks_disable(mtk); >>> >> >> Could you share details of the NULL pointer dereference, (backtrace). > > This bug was found by our QA staff while doing 500 times plug-in and > plug-out devices. The backtrace I have was recorded by QA and I didn't > reproduce this issue on my own environment. However, after applied this > patch the issue seems resolve. Here is the backtrace: > > Exception Class: Kernel (KE) > PC is at [<ffffff8008cccbc0>] xhci_irq+0x728/0x2364 > LR is at [<ffffff8008ccc788>] xhci_irq+0x2f0/0x2364 > > Current Executing Process: > [iptables, 859][netdagent, 770] > > Backtrace: > [<ffffff80080ead58>] __atomic_notifier_call_chain+0xa8/0x130 > [<ffffff80080eb6d4>] notify_die+0x84/0xac > [<ffffff800808e874>] die+0x1d8/0x3b8 > [<ffffff80080a89b0>] __do_kernel_fault+0x178/0x188 > [<ffffff80080a81b4>] do_page_fault+0x44/0x3b0 > [<ffffff80080a811c>] do_translation_fault+0x44/0x98 > [<ffffff8008080e08>] do_mem_abort+0x4c/0x128 > [<ffffff80080832d0>] el1_da+0x24/0x3c > [<ffffff8008cccbc0>] xhci_irq+0x728/0x2364 > [<ffffff8008c98804>] usb_hcd_irq+0x2c/0x44 > [<ffffff8008179bb0>] __handle_irq_event_percpu+0x26c/0x4a4 > [<ffffff8008179ec8>] handle_irq_event+0x5c/0xd0 > [<ffffff800817e3c0>] handle_fasteoi_irq+0x10c/0x1e0 > [<ffffff80081787b0>] __handle_domain_irq+0x32c/0x738 > [<ffffff800808159c>] gic_handle_irq+0x174/0x1c4 > [<ffffff8008083cf8>] el0_irq_naked+0x50/0x5c > [<ffffffffffffffff>] 0xffffffffffffffff >
Thanks, Could you help me find out which line of code xhci_irq+0x728 is in your case.
As Guenter pointed out there is a risk of turning the NULL pointer dereference into a use after free if we just solve this by setting xhci->shared_hcd = NULL later.
If you still have that kernel around, and xhci is compiled in: gdb vmlinux gdb li *(xhci_irq+0x728)
-Mathias
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