On 26/8/21 5:58 pm, Daniel Vetter wrote:
On Thu, Aug 26, 2021 at 10:01:18AM +0800, Desmond Cheong Zhi Xi wrote:
In a future patch, a read lock on drm_device.master_rwsem is
held in the ioctl handler before the check for ioctl
permissions. However, this inverts the lock hierarchy of
drm_global_mutex --> master_rwsem.
To avoid this, we do some prep work to grab the drm_global_mutex
before checking for ioctl permissions.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
---
drivers/gpu/drm/drm_ioctl.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index d25713b09b80..158629d88319 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -772,19 +772,19 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata,
if (drm_dev_is_unplugged(dev))
return -ENODEV;
+ /* Enforce sane locking for modern driver ioctls. */
+ if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & DRM_UNLOCKED))
Maybe have a local bool locked_ioctl for this so it's extremely clear it's
the same condition in both?
Either way: Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Thanks for the suggestion and review. Sounds good, I'll update and send
out a new version.
(Sorry for delays, been busy with moving)
+ mutex_lock(&drm_global_mutex);
+
retcode = drm_ioctl_permit(flags, file_priv);
if (unlikely(retcode))
- return retcode;
+ goto out;
- /* Enforce sane locking for modern driver ioctls. */
- if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) ||
- (flags & DRM_UNLOCKED))
- retcode = func(dev, kdata, file_priv);
- else {
- mutex_lock(&drm_global_mutex);
- retcode = func(dev, kdata, file_priv);
+ retcode = func(dev, kdata, file_priv);
+
+out:
+ if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & DRM_UNLOCKED))
mutex_unlock(&drm_global_mutex);
- }
return retcode;
}
EXPORT_SYMBOL(drm_ioctl_kernel);
--
2.25.1
