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:
- 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.
- 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).
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.
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.price@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;