I would Cc it to stable just in case tbh. I picked up on this one since KASAN was picking up on some of the memcpy() calls around here going out of bounds. I can include some of the backtraces from that if needed.
On Wed, 2016-05-04 at 19:11 +0200, Daniel Vetter wrote:
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@vger.kernel.org Signed-off-by: Lyude cpaul@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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