[PATCH] event: Cheking for NULL before dereferencing the pointer.

[Srivardhan]

> -----Original Message-----
> From: Pekka Paalanen [mailto:ppaalanen at gmail.com]
> Sent: Friday, May 09, 2014 3:09 PM
> To: Srivardhan
> Cc: 'Hardening'; wayland-devel at lists.freedesktop.org
> Subject: Re: [PATCH] event: Cheking for NULL before dereferencing the
> pointer.
> 
> On Fri, 09 May 2014 14:56:14 +0530
> Srivardhan <sri.hebbar at samsung.com> wrote:
> 
> >
> >
> > > -----Original Message-----
> > > From: wayland-devel [mailto:wayland-devel-
> > > bounces at lists.freedesktop.org] On Behalf Of Hardening
> > > Sent: Friday, May 09, 2014 1:08 PM
> > > To: wayland-devel at lists.freedesktop.org
> > > Subject: Re: [PATCH] event: Cheking for NULL before dereferencing
> > > the pointer.
> > >
> > > Le 09/05/2014 08:43, Srivardhan Hebbar a écrit :
> > > > Checking for NULL before dereferencing the wl_event_source pointer
> > > > so as to avoid crash.
> > > >
> > > > Signed-off-by: Srivardhan Hebbar <sri.hebbar at samsung.com>
> > > > ---
> > > >   src/event-loop.c |    7 ++++++-
> > > >   1 file changed, 6 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/src/event-loop.c b/src/event-loop.c index
> > > > 9790cde..b62d16e 100644
> > > > --- a/src/event-loop.c
> > > > +++ b/src/event-loop.c
> > > > @@ -312,7 +312,12 @@ wl_event_source_check(struct
> wl_event_source
> > > *source)
> > > >   WL_EXPORT int
> > > >   wl_event_source_remove(struct wl_event_source *source)
> > > >   {
> > > > -	struct wl_event_loop *loop = source->loop;
> > > > +	struct wl_event_loop *loop;
> > > > +
> > > > +	if (source == NULL)
> > > > +		return 0;
> > > > +
> > > > +	loop = source->loop;
> > > >
> > > >   	/* We need to explicitly remove the fd, since closing the fd
> > > >   	 * isn't enough in case we've dup'ed the fd. */
> > > >
> > >
> > > Hello Srivardhan,
> > >
> > > do you have a case where this check is hit ? I may be wrong but
> > > having no loop associated with a source event is not supposed to
> > > happen. So my guess is that a caller of wl_event_source_remove has
> > > forgotten to nullify the
> > event
> > > source after the call.
> >
> > Hi,
> >
> > I was going through the code of Weston. In the main function in
> > compositor.c
> > wl_event_loop_add_signal() is called to allocate the memory for
> > signals[](Line no: 4196. struct wl_event_source *signals[4]). The
> > function returns NULL if memory allocation failed. After that there is
> > no NULL check for 'signals'. In the end while clearing up, this
> > function is called. So if memory allocation failed then a NULL is
> > passed to this function. Hence adding code to check for the NULL.
> 
> Hi,
> 
> I think we should be fixing the caller instead of
wl_event_source_remove(). I
> do not believe NULL is a valid argument for it, so the bug is in the
caller.
> 
> If any wl_event_loop_add_signal() in Weston fails, it would be a reason to
> exit with an error.
> 

Oh... k... Will fix that and send the patch...

In general isn't it fine to check for NULL before dereferencing? 

Thank-you,
Hebbar
> 
> Thanks,
> pq