From eb197f7d60f00d0f5b1b3505dfc86a7e36045a3e Mon Sep 17 00:00:00 2001 From: Danilo Krummrich Date: Sun, 28 Jun 2026 16:53:36 +0200 Subject: [PATCH] drm: fix race between partial drm_dev_register() failure and ioctl If drm_dev_register() fails after registering a minor (e.g. render minor registered, primary minor fails), userspace could have opened the first minor and entered a drm_dev_enter() critical section. Since the unplugged flag was never set, the ioctl proceeds while the error path tears down device resources. Fix this by introducing drm_dev_synchronize_unplug(), which sets the unplugged flag and waits for the SRCU barrier, ensuring all in-flight drm_dev_enter() critical sections complete before cleanup proceeds; call it on the error path of drm_dev_register(). Fixes: bee330f3d672 ("drm: Use srcu to protect drm_device.unplugged") Cc: stable@vger.kernel.org Reported-by: sashiko-bot@kernel.org Closes: https://lore.kernel.org/all/20260620190648.2E9F61F000E9@smtp.kernel.org/ Reviewed-by: Alexandre Courbot Reviewed-by: Lyude Paul Tested-by: Deborah Brouwer Link: https://patch.msgid.link/20260628145406.2107056-17-dakr@kernel.org Signed-off-by: Danilo Krummrich --- drivers/gpu/drm/drm_drv.c | 34 +++++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index 675675480da4..e890052061f3 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -473,6 +473,22 @@ void drm_dev_exit(int idx) } EXPORT_SYMBOL(drm_dev_exit); +/* + * Mark the device as unplugged and wait for any in-flight drm_dev_enter() + * critical sections to complete. + */ +static void drm_dev_synchronize_unplug(struct drm_device *dev) +{ + /* + * After synchronizing any critical read section is guaranteed to see + * the new value of ->unplugged, and any critical section which might + * still have seen the old value of ->unplugged is guaranteed to have + * finished. + */ + dev->unplugged = true; + synchronize_srcu(&drm_unplug_srcu); +} + /** * drm_dev_unplug - unplug a DRM device * @dev: DRM device @@ -485,15 +501,7 @@ EXPORT_SYMBOL(drm_dev_exit); */ void drm_dev_unplug(struct drm_device *dev) { - /* - * After synchronizing any critical read section is guaranteed to see - * the new value of ->unplugged, and any critical section which might - * still have seen the old value of ->unplugged is guaranteed to have - * finished. - */ - dev->unplugged = true; - synchronize_srcu(&drm_unplug_srcu); - + drm_dev_synchronize_unplug(dev); drm_dev_unregister(dev); /* Clear all CPU mappings pointing to this device */ @@ -1091,6 +1099,7 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags) goto err_minors; dev->registered = true; + dev->unplugged = false; if (driver->load) { ret = driver->load(dev, flags); @@ -1118,6 +1127,13 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags) if (dev->driver->unload) dev->driver->unload(dev); err_minors: + /* + * If a minor was registered before the failure, userspace could have + * opened it and entered a drm_dev_enter() critical section. Ensure all + * such sections complete before we clean up. + */ + drm_dev_synchronize_unplug(dev); + remove_compat_control_link(dev); drm_minor_unregister(dev, DRM_MINOR_ACCEL); drm_minor_unregister(dev, DRM_MINOR_PRIMARY);