Re: [PATCH v2] USB: EHCI: fix dereference of ERR_PTR

From: Sudip Mukherjee
Date: Fri Sep 18 2015 - 01:48:34 EST


On Wed, Sep 16, 2015 at 12:54:03PM -0400, Alan Stern wrote:
> 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>
> > ---
<snip>
> > @@ -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().
Yes, I should have looked more before sending. Sorry for the noise.
But in those checkes for find_tt() only IS_ERR is checked, shouldn't we
check for IS_ERR_OR_NULL as find_tt() can return NULL also?

regards
sudip
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