[PATCH libdrm] Fix memory leak with drmModeGetConnectorCurrent()

[Ville Syrjälä]

On Tue, Dec 15, 2015 at 02:05:45PM +0000, Chris Wilson wrote:
> On Tue, Dec 15, 2015 at 03:59:28PM +0200, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > drmModeGetConnectorCurrent() must provide temporary storage for the
> > kernel to fill in at least one mode (asking for !=0 modes is how
> > you prevent the heavyweight probe in the kernel). Currently we malloc
> > that temp storage but we fail to free it before overwriting the
> > pointer with the address of the actual storage we use to store the
> > real mode list we get from the kernel in the second ioctl call.
> > 
> > Let's just keep the temporary storage on the stack and thus we avoid the
> > leak and also eliminate some pointless mallocs.
> > 
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Fixes: 5ed5fa10600f ("mode: Retrieve only the current information for a Connector")
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >  xf86drmMode.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> > 
> > diff --git a/xf86drmMode.c b/xf86drmMode.c
> > index ab6b5195e8d3..7710061865ee 100644
> > --- a/xf86drmMode.c
> > +++ b/xf86drmMode.c
> > @@ -475,12 +475,13 @@ _drmModeGetConnector(int fd, uint32_t connector_id, int probe)
> >  {
> >  	struct drm_mode_get_connector conn, counts;
> >  	drmModeConnectorPtr r = NULL;
> > +	struct drm_mode_modeinfo stack_mode;
> >  
> >  	memclear(conn);
> >  	conn.connector_id = connector_id;
> >  	if (!probe) {
> >  		conn.count_modes = 1;
> > -		conn.modes_ptr = VOID2U64(drmMalloc(sizeof(struct drm_mode_modeinfo)));
> > +		conn.modes_ptr = VOID2U64(&stack_mode);
> >  	}
> 
> If you just made this change, we wouldn't need the hunks below (and I
> wouln't have to look at so much shouting).

That was my initial plan, but then I figured we could also skip the
other malloc for disconnected connectors.

> 
> Either way,
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre

-- 
Ville Syrjälä
Intel OTC