[PATCH 3/5] drm: Possible lock priority escalation.

[Peter Antoine]

If an application that has a driver lock created, wants the lock the
kernel context, it is not allowed to. If the call to drm_lock has a
context of 0, it is rejected. If you set the context to _DRM_LOCK_CONT
then call drm lock, it will pass the context == DRM_KERNEL_CONTEXT checks.
But as the DRM_LOCK_CONT bits are not part of the context id this allows
operations on the DRM_KERNEL_CONTEXT.

Issue: VIZ-5485
Signed-off-by: Peter Antoine <peter.antoine at intel.com>
---
 drivers/gpu/drm/drm_context.c | 6 +++---
 drivers/gpu/drm/drm_lock.c    | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_context.c b/drivers/gpu/drm/drm_context.c
index 96350d1..1febcd3 100644
--- a/drivers/gpu/drm/drm_context.c
+++ b/drivers/gpu/drm/drm_context.c
@@ -123,7 +123,7 @@ void drm_legacy_ctxbitmap_flush(struct drm_device *dev, struct drm_file *file)
 
 	list_for_each_entry_safe(pos, tmp, &dev->ctxlist, head) {
 		if (pos->tag == file &&
-		    pos->handle != DRM_KERNEL_CONTEXT) {
+		    _DRM_LOCKING_CONTEXT(pos->handle) != DRM_KERNEL_CONTEXT) {
 			if (dev->driver->context_dtor)
 				dev->driver->context_dtor(dev, pos->handle);
 
@@ -342,7 +342,7 @@ int drm_legacy_addctx(struct drm_device *dev, void *data,
 	struct drm_ctx *ctx = data;
 
 	ctx->handle = drm_legacy_ctxbitmap_next(dev);
-	if (ctx->handle == DRM_KERNEL_CONTEXT) {
+	if (_DRM_LOCKING_CONTEXT(ctx->handle) == DRM_KERNEL_CONTEXT) {
 		/* Skip kernel's context and get a new one. */
 		ctx->handle = drm_legacy_ctxbitmap_next(dev);
 	}
@@ -449,7 +449,7 @@ int drm_legacy_rmctx(struct drm_device *dev, void *data,
 	struct drm_ctx *ctx = data;
 
 	DRM_DEBUG("%d\n", ctx->handle);
-	if (ctx->handle != DRM_KERNEL_CONTEXT) {
+	if (_DRM_LOCKING_CONTEXT(ctx->handle) != DRM_KERNEL_CONTEXT) {
 		if (dev->driver->context_dtor)
 			dev->driver->context_dtor(dev, ctx->handle);
 		drm_legacy_ctxbitmap_free(dev, ctx->handle);
diff --git a/drivers/gpu/drm/drm_lock.c b/drivers/gpu/drm/drm_lock.c
index 070dd5d..94500930 100644
--- a/drivers/gpu/drm/drm_lock.c
+++ b/drivers/gpu/drm/drm_lock.c
@@ -63,7 +63,7 @@ int drm_legacy_lock(struct drm_device *dev, void *data,
 
 	++file_priv->lock_count;
 
-	if (lock->context == DRM_KERNEL_CONTEXT) {
+	if (_DRM_LOCKING_CONTEXT(lock->context) == DRM_KERNEL_CONTEXT) {
 		DRM_ERROR("Process %d using kernel context %d\n",
 			  task_pid_nr(current), lock->context);
 		return -EINVAL;
@@ -153,7 +153,7 @@ int drm_legacy_unlock(struct drm_device *dev, void *data, struct drm_file *file_
 	struct drm_lock *lock = data;
 	struct drm_master *master = file_priv->master;
 
-	if (lock->context == DRM_KERNEL_CONTEXT) {
+	if (_DRM_LOCKING_CONTEXT(lock->context) == DRM_KERNEL_CONTEXT) {
 		DRM_ERROR("Process %d using kernel context %d\n",
 			  task_pid_nr(current), lock->context);
 		return -EINVAL;
-- 
1.9.1