Re: [PATCH] usb: gadget: u_serial: Disable ep before setting port to null to fix the crash caused by port being null

[Michael Nazzareno Trimarchi]

Hi 胡连勤

On Mon, Sep 30, 2024 at 3:48 AM 胡连勤 <hulianqin@xxxxxxxx> wrote:
>
> From: Lianqin Hu <hulianqin@xxxxxxxx>
>
> Considering that in some extreme cases, when performing the
> unbinding operation, gserial_disconnect has cleared gser->ioport,
> which triggers gadget reconfiguration, and then calls gs_read_complete,
> resulting in access to a null pointer. Therefore, ep is disabled before
> gserial_disconnect sets port to null to prevent this from happening.
>
> Unable to handle kernel NULL pointer dereference at
> virtual address 00000000000001a8
> pc : gs_read_complete+0x58/0x240
> lr : usb_gadget_giveback_request+0x40/0x160
> sp : ffffffc00f1539c0
> x29: ffffffc00f1539c0 x28: ffffff8002a30000 x27: 0000000000000000
> x26: ffffff8002a30000 x25: 0000000000000000 x24: ffffff8002a30000
> x23: ffffff8002ff9a70 x22: ffffff898e7a7b00 x21: ffffff803c9af9d8
> x20: ffffff898e7a7b00 x19: 00000000000001a8 x18: ffffffc0099fd098
> x17: 0000000000001000 x16: 0000000080000000 x15: 0000000ac1200000
> x14: 0000000000000003 x13: 000000000000d5e8 x12: 0000000355c314ac
> x11: 0000000000000015 x10: 0000000000000012 x9 : 0000000000000008
> x8 : 0000000000000000 x7 : 0000000000000000 x6 : ffffff887cd12000
> x5 : 0000000000000002 x4 : ffffffc00f9b07f0 x3 : ffffffc00f1538d0
> x2 : 0000000000000001 x1 : 0000000000000000 x0 : 00000000000001a8
> Call trace:
> gs_read_complete+0x58/0x240
> usb_gadget_giveback_request+0x40/0x160
> dwc3_remove_requests+0x170/0x484
> dwc3_ep0_out_start+0xb0/0x1d4
> __dwc3_gadget_start+0x25c/0x720
> kretprobe_trampoline.cfi_jt+0x0/0x8
> kretprobe_trampoline.cfi_jt+0x0/0x8
> udc_bind_to_driver+0x1d8/0x300
> usb_gadget_probe_driver+0xa8/0x1dc
> gadget_dev_desc_UDC_store+0x13c/0x188
> configfs_write_iter+0x160/0x1f4
> vfs_write+0x2d0/0x40c
> ksys_write+0x7c/0xf0
> __arm64_sys_write+0x20/0x30
> invoke_syscall+0x60/0x150
> el0_svc_common+0x8c/0xf8
> do_el0_svc+0x28/0xa0
> el0_svc+0x24/0x84
> el0t_64_sync_handler+0x88/0xec
> el0t_64_sync+0x1b4/0x1b8
> Code: aa1f03e1 aa1303e0 52800022 2a0103e8 (88e87e62)
> ---[ end trace 938847327a739172 ]---
> Kernel panic - not syncing: Oops: Fatal exception
>
> Fixes: c1dca562be8a ("usb gadget: split out serial core")
> Cc: stable@xxxxxxxxxxxxxxx
>
> Suggested-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Lianqin Hu <hulianqin@xxxxxxxx>
> ---
>  drivers/usb/gadget/function/u_serial.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index b394105e55d6..1712e9cd08be 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -1395,6 +1395,10 @@ void gserial_disconnect(struct gserial *gser)
>         /* REVISIT as above: how best to track this? */
>         port->port_line_coding = gser->port_line_coding;
>
> +       /* disable endpoints, aborting down any active I/O */
> +       usb_ep_disable(gser->out);
> +       usb_ep_disable(gser->in);
> +

According to the review from here
https://lore.kernel.org/lkml/64ad7661-4551-7b00-604b-6e15da23a1c7@xxxxxxxxxxx/T/

Greg and I suggest to abort before but Prashanth K comment  "
Not sure about this case, I think generally we need stop IO before
disabling EP, otherwise TX/RX functions may queue requests while EP is
getting disabled, thats why i think port is removed before ep_disable.
Moreover these callbacks (complete/suspend/resume etc) comes from UDC
and can be async, so better to use locks to prevent these kind of races."

Michael

>         port->port_usb = NULL;
>         gser->ioport = NULL;
>         if (port->port.count > 0) {
> @@ -1406,10 +1410,6 @@ void gserial_disconnect(struct gserial *gser)
>         spin_unlock(&port->port_lock);
>         spin_unlock_irqrestore(&serial_port_lock, flags);
>
> -       /* disable endpoints, aborting down any active I/O */
> -       usb_ep_disable(gser->out);
> -       usb_ep_disable(gser->in);
> -
>         /* finally, free any unused/unusable I/O buffers */
>         spin_lock_irqsave(&port->port_lock, flags);
>         if (port->port.count == 0)
> --
> 2.39.0
>


-- 
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@xxxxxxxxxxxxxxxxxxxx
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