Re: [PATCH] drivers: usb: host: fix NULL pointer dereferences triggered by unhandled errors in xhci_create_rhub_port_array()

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Apr 21, 2022 at 05:42:36PM +0800, Zixuan Fu wrote:
> In xhci_create_rhub_port_array(), when rhub->num_ports is zero, 
> rhub->ports would not be set; when kcalloc_node() fails, rhub->ports
> would be set to NULL. In these two cases, xhci_create_rhub_port_array()
> just returns void, and thus its callers are unaware of the error.
> 
> Then rhub->ports is dereferenced in xhci_usb3_hub_descriptor() or 
> xhci_usb2_hub_descriptor().
> 
> To fix the bug, xhci_setup_port_arrays() should return an integer to 
> indicate a possible error, and its callers should handle the error.
> 
> Here is the log when this bug occurred in our fault-injection testing:
> 
> [   24.001309] BUG: kernel NULL pointer dereference, address: 0000000000000000
> ...
> [   24.003992] RIP: 0010:xhci_hub_control+0x3f5/0x60d0 [xhci_hcd]
> ...
> [   24.009803] Call Trace:
> [   24.010014]  <TASK>
> [   24.011310]  usb_hcd_submit_urb+0x1233/0x1fd0
> [   24.017071]  usb_start_wait_urb+0x115/0x310
> [   24.017641]  usb_control_msg+0x28a/0x450
> [   24.019046]  hub_probe+0xb16/0x2320
> [   24.019757]  usb_probe_interface+0x4f1/0x930
> [   24.019765]  really_probe+0x33d/0x970
> [   24.019768]  __driver_probe_device+0x157/0x210
> [   24.019772]  driver_probe_device+0x4f/0x340
> [   24.019775]  __device_attach_driver+0x2ee/0x3a0
> ...
> 
> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
> Signed-off-by: Zixuan Fu <r33s3n6@gmail.com>
> ---
>  drivers/usb/host/xhci-mem.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index bbb27ee2c6a3..024515346c39 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -2235,7 +2235,7 @@ static void xhci_add_in_port(struct xhci_hcd *xhci, unsigned int num_ports,
>  	/* FIXME: Should we disable ports not in the Extended Capabilities? */
>  }
>  
> -static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
> +static int xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>  					struct xhci_hub *rhub, gfp_t flags)
>  {
>  	int port_index = 0;
> @@ -2243,11 +2243,11 @@ static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>  	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
>  
>  	if (!rhub->num_ports)
> -		return;
> +		return -EINVAL;
>  	rhub->ports = kcalloc_node(rhub->num_ports, sizeof(*rhub->ports),
>  			flags, dev_to_node(dev));
>  	if (!rhub->ports)
> -		return;
> +		return -ENOMEM;
>  
>  	for (i = 0; i < HCS_MAX_PORTS(xhci->hcs_params1); i++) {
>  		if (xhci->hw_ports[i].rhub != rhub ||
> @@ -2259,6 +2259,7 @@ static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>  		if (port_index == rhub->num_ports)
>  			break;
>  	}
> +	return 0;
>  }
>  
>  /*
> @@ -2277,6 +2278,7 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
>  	int cap_count = 0;
>  	u32 cap_start;
>  	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
> +	int ret;
>  
>  	num_ports = HCS_MAX_PORTS(xhci->hcs_params1);
>  	xhci->hw_ports = kcalloc_node(num_ports, sizeof(*xhci->hw_ports),
> @@ -2367,8 +2369,13 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
>  	 * Not sure how the USB core will handle a hub with no ports...
>  	 */
>  
> -	xhci_create_rhub_port_array(xhci, &xhci->usb2_rhub, flags);
> -	xhci_create_rhub_port_array(xhci, &xhci->usb3_rhub, flags);
> +	ret = xhci_create_rhub_port_array(xhci, &xhci->usb2_rhub, flags);
> +	if (ret)
> +		return ret;
> +
> +	ret = xhci_create_rhub_port_array(xhci, &xhci->usb3_rhub, flags);
> +	if (ret)
> +		return ret;

What about the memory allocated by the first call to
xhci_create_rhub_port_array()?  Is that now lost?  Same for everything
else allocated before these calls, how is that cleaned up properly?

thanks,

greg k-h