Hi Steven, On Mon, Jul 12, 2021 at 10:31:52PM +0100, Steven Price wrote: > On 12/07/2021 17:50, Laurent Pinchart wrote: > > On Mon, Jul 12, 2021 at 04:57:58PM +0100, Steven Price wrote: > >> When bailing out due to the sanity check the iterator value needs to be > >> freed because the early return prevents for_each_child_of_node() from > >> doing the dereference itself. > >> > >> Fixes: 4ee48cc5586b ("drm: of: Fix double-free bug") > > > > I don't think the Fixes tag is correct, the issue was already present > > before 4ee48cc5586b. The fix looks right though. > > I'm not sure quite what you mean by "already present". As I understand > it the timeline was: > > 1. 6529007522de drm: of: Add drm_of_lvds_get_dual_link_pixel_order > The function was originally added. This made the mistake twice of > calling of_node_put() on the wrong variable (remote_port rather than > endpoint).
Correct. > 2. 4ee48cc5586b drm: of: Fix double-free bug > One of the of_node_put() calls was removed as it was a double-free. > This left the first incorrect of_node_put() in place, and the second > is now a straight leak. That's right, but this commit didn't introduce the leak, it was already there in 6529007522de (in addition to the double-free). > 3. b557a5f8da57 drm/of: free the right object > This (correctly) fixes the first of_node_put() to free endpoint. And > the post from Daniel was what caused me to look. > > 4. This patch > Reintroduces the of_node_put() removed in (2) but putting endpoint > rather than remote_port. > > I've put (2) in the Fixes line as this patch is fixing the leak > introduced by that patch, but that in itself was of course 'fixing' the > double free of the original patch. > > >> Signed-off-by: Steven Price <steven.pr...@arm.com> > >> --- > >> drivers/gpu/drm/drm_of.c | 4 +++- > >> 1 file changed, 3 insertions(+), 1 deletion(-) > >> > >> Daniel's email[1] made me take a look at this function and it appears > >> that for_each_child_of_node()'s interface had caused a bad bug fix due > >> to the hidden reference counting in the iterator. > >> > >> [1] https://lore.kernel.org/r/YOxQ5TbkNrqCGBDJ%40phenom.ffwll.local > >> > >> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c > >> index 197c57477344..997b8827fed2 100644 > >> --- a/drivers/gpu/drm/drm_of.c > >> +++ b/drivers/gpu/drm/drm_of.c > >> @@ -331,8 +331,10 @@ static int drm_of_lvds_get_remote_pixels_type( > >> * configurations by passing the endpoints explicitly to > >> * drm_of_lvds_get_dual_link_pixel_order(). > >> */ > >> - if (!current_pt || pixels_type != current_pt) > >> + if (!current_pt || pixels_type != current_pt) { > >> + of_node_put(endpoint); > >> return -EINVAL; > >> + } > >> } > >> > >> return pixels_type; -- Regards, Laurent Pinchart