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Subject[PATCH 2/3] drm/fb_helper: Fix references to dev->mode_config.num_connector
Date
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@vger.kernel.org
Signed-off-by: Lyude <cpaul@redhat.com>
---
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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