On Wed, May 04, 2016 at 11:28:52AM -0400, Lyude wrote:
> During boot, MST hotplugs are generally expected (even if no physical
> hotplugging occurs) and result in DRM's connector topology changing.
> This means that using num_connector from the current mode configuration
> can lead to the number of connectors changing under us. This can lead to
> some nasty scenarios in fbcon:
>
> - We allocate an array to the size of dev->mode_config.num_connectors.
> - MST hotplug occurs, dev->mode_config.num_connectors gets incremented.
> - We try to loop through each element in the array using the new value
> of dev->mode_config.num_connectors, and end up going out of bounds
> since dev->mode_config.num_connectors is now larger then the array we
> allocated.
>
> fb_helper->connector_count however, will always remain consistent while
> we do a modeset in fb_helper.
>
> Cc: stable at vger.kernel.org
> Signed-off-by: Lyude <cpaul at redhat.com>
Ok, this one looks like it's indeed in the same critical section (within
drm_setup_outputs) as where we allocate the fb helper connector array. So
I think this one here is not needed to fix a bug?
Still makes sense as a patch, but not with cc: stable I think.
-Daniel
> ---
> drivers/gpu/drm/drm_fb_helper.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 855108e..15204c0 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1914,7 +1914,7 @@ static int drm_pick_crtcs(struct drm_fb_helper
> *fb_helper,
> if (modes[n] == NULL)
> return best_score;
>
> - crtcs = kzalloc(dev->mode_config.num_connector *
> + crtcs = kzalloc(fb_helper->connector_count *
> sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
> if (!crtcs)
> return best_score;
> @@ -1960,7 +1960,7 @@ static int drm_pick_crtcs(struct drm_fb_helper
> *fb_helper,
> if (score > best_score) {
> best_score = score;
> memcpy(best_crtcs, crtcs,
> - dev->mode_config.num_connector *
> + fb_helper->connector_count *
> sizeof(struct drm_fb_helper_crtc *));
> }
> }
> --
> 2.5.5
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
