Re: [PATCH] USB: Avoid NULL pointer dereference in usb_disconnect()

From: wangyanqing
Date: Mon Jul 11 2011 - 05:39:17 EST


On Mon, Jul 11, 2011 at 11:21:18AM +0200, Jesper Juhl wrote:
> If, in drivers/usb/core/hub.c::usb_disconnect(), 'udev' is NULL, then
> we'll never get to the printing of a debug message and returning from
> the function since we'll have already dereferenced the NULL pointer in
> the bus_to_hcd(udev->bus) call.
> This patch moves the dereference to after the test for NULL, thus
> avoiding that potential crash.
>
> Signed-off-by: Jesper Juhl <jj@xxxxxxxxxxxxx>
> ---
> drivers/usb/core/hub.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> disclaimer: compile tested only.
>
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index a428aa0..0a98c76 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1634,13 +1634,15 @@ void usb_disconnect(struct usb_device **pdev)
> {
> struct usb_device *udev = *pdev;
> int i;
> - struct usb_hcd *hcd = bus_to_hcd(udev->bus);
> + struct usb_hcd *hcd;
>
> if (!udev) {
> pr_debug ("%s nodev\n", __func__);
> return;
> }
>
> + hcd = bus_to_hcd(udev->bus);
> +
> /* mark the device as inactive, so any further urb submissions for
> * this device (and any of its children) will fail immediately.
> * this quiesces everything except pending urbs.
> --
> 1.7.6
>
>
> --
> Jesper Juhl <jj@xxxxxxxxxxxxx> http://www.chaosbits.net/
> Don't top-post http://www.catb.org/jargon/html/T/top-post.html
> Plain text mails only, please.
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
Hello,All.Just a question,should we add the NULL checker code at everywhere that
dereference pointer in kernel? If so,it will scare me.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/