On Wed, 16 Sep 2015, Sudip Mukherjee wrote:
> On error find_tt() returns either a NULL pointer or the error value in
> ERR_PTR. But we were dereferencing it directly without even checking if
> find_tt() returned a valid pointer or not.
>
> Signed-off-by: Sudip Mukherjee <sudip@xxxxxxxxxxxxxxx>
> ---
>
> v2: used IS_ERR_OR_NULL (didn't know it was there. thanks)
>
>
> drivers/usb/host/ehci-sched.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
> index f9a3327..de75343 100644
> --- a/drivers/usb/host/ehci-sched.c
> +++ b/drivers/usb/host/ehci-sched.c
> @@ -257,6 +257,8 @@ static void reserve_release_intr_bandwidth(struct ehci_hcd *ehci,
> /* FS/LS bus bandwidth */
> if (tt_usecs) {
> tt = find_tt(qh->ps.udev);
> + if (IS_ERR_OR_NULL(tt))
> + return;
> if (sign > 0)
> list_add_tail(&qh->ps.ps_list, &tt->ps_list);
> else
> @@ -1373,6 +1375,8 @@ static void reserve_release_iso_bandwidth(struct ehci_hcd *ehci,
> }
>
> tt = find_tt(stream->ps.udev);
> + if (IS_ERR_OR_NULL(tt))
> + return;
> if (sign > 0)
> list_add_tail(&stream->ps.ps_list, &tt->ps_list);
> else
This patch isn't needed. In both reserve_release_intr_bandwidth() and
reserve_release_iso_bandwidth() it is known that find_tt() will return
a valid pointer.
This is because each of those functions is called from only one place.
For example, reserve_release_intr_bandwidth() is called only at the end
of qh_schedule(). But near the start of qh_schedule() there is earlier
call to tt_find(), and there we do test for error pointers. If the
first call doesn't return an error then the second call won't either.
The same sort of thing happens in reserve_release_iso_bandwidth().
Alan Stern
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
