[PATCH] drm/vmwgfx: Fix possible invalid drm gem put calls

[Zack Rusin]

From: Zack Rusin <zackr at vmware.com>

vmw_bo_unreference sets the input buffer to null on exit, resulting in
null ptr deref's on the subsequent drm gem put calls.

This went unnoticed because only very old userspace would be exercising
those paths but it wouldn't be hard to hit on old distros with brand
new kernels.

Introduce a new function that abstracts unrefing of user bo's to make
the code cleaner and more explicit.

Signed-off-by: Zack Rusin <zackr at vmware.com>
Reported-by: Ian Forbes <iforbes at vmware.com>
Fixes: 9ef8d83e8e25 ("drm/vmwgfx: Do not drop the reference to the handle too soon")
Cc: <stable at vger.kernel.org> # v6.4+
---
 drivers/gpu/drm/vmwgfx/vmwgfx_bo.c      | 6 ++----
 drivers/gpu/drm/vmwgfx/vmwgfx_bo.h      | 8 ++++++++
 drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 6 ++----
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c     | 6 ++----
 drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c | 3 +--
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c  | 3 +--
 6 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
index 82094c137855..c43853597776 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
@@ -497,10 +497,9 @@ static int vmw_user_bo_synccpu_release(struct drm_file *filp,
 		if (!(flags & drm_vmw_synccpu_allow_cs)) {
 			atomic_dec(&vmw_bo->cpu_writers);
 		}
-		ttm_bo_put(&vmw_bo->tbo);
+		vmw_user_bo_unref(vmw_bo);
 	}
 
-	drm_gem_object_put(&vmw_bo->tbo.base);
 	return ret;
 }
 
@@ -540,8 +539,7 @@ int vmw_user_bo_synccpu_ioctl(struct drm_device *dev, void *data,
 			return ret;
 
 		ret = vmw_user_bo_synccpu_grab(vbo, arg->flags);
-		vmw_bo_unreference(&vbo);
-		drm_gem_object_put(&vbo->tbo.base);
+		vmw_user_bo_unref(vbo);
 		if (unlikely(ret != 0)) {
 			if (ret == -ERESTARTSYS || ret == -EBUSY)
 				return -EBUSY;
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.h b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.h
index 50a836e70994..1d433fceed3d 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.h
@@ -195,6 +195,14 @@ static inline struct vmw_bo *vmw_bo_reference(struct vmw_bo *buf)
 	return buf;
 }
 
+static inline void vmw_user_bo_unref(struct vmw_bo *vbo)
+{
+	if (vbo) {
+		ttm_bo_put(&vbo->tbo);
+		drm_gem_object_put(&vbo->tbo.base);
+	}
+}
+
 static inline struct vmw_bo *to_vmw_bo(struct drm_gem_object *gobj)
 {
 	return container_of((gobj), struct vmw_bo, tbo.base);
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index 6b9aa2b4ef54..25b96821df0f 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -1164,8 +1164,7 @@ static int vmw_translate_mob_ptr(struct vmw_private *dev_priv,
 	}
 	vmw_bo_placement_set(vmw_bo, VMW_BO_DOMAIN_MOB, VMW_BO_DOMAIN_MOB);
 	ret = vmw_validation_add_bo(sw_context->ctx, vmw_bo);
-	ttm_bo_put(&vmw_bo->tbo);
-	drm_gem_object_put(&vmw_bo->tbo.base);
+	vmw_user_bo_unref(vmw_bo);
 	if (unlikely(ret != 0))
 		return ret;
 
@@ -1221,8 +1220,7 @@ static int vmw_translate_guest_ptr(struct vmw_private *dev_priv,
 	vmw_bo_placement_set(vmw_bo, VMW_BO_DOMAIN_GMR | VMW_BO_DOMAIN_VRAM,
 			     VMW_BO_DOMAIN_GMR | VMW_BO_DOMAIN_VRAM);
 	ret = vmw_validation_add_bo(sw_context->ctx, vmw_bo);
-	ttm_bo_put(&vmw_bo->tbo);
-	drm_gem_object_put(&vmw_bo->tbo.base);
+	vmw_user_bo_unref(vmw_bo);
 	if (unlikely(ret != 0))
 		return ret;
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index b62207be3363..1489ad73c103 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -1665,10 +1665,8 @@ static struct drm_framebuffer *vmw_kms_fb_create(struct drm_device *dev,
 
 err_out:
 	/* vmw_user_lookup_handle takes one ref so does new_fb */
-	if (bo) {
-		vmw_bo_unreference(&bo);
-		drm_gem_object_put(&bo->tbo.base);
-	}
+	if (bo)
+		vmw_user_bo_unref(bo);
 	if (surface)
 		vmw_surface_unreference(&surface);
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c b/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c
index 7e112319a23c..fb85f244c3d0 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c
@@ -451,8 +451,7 @@ int vmw_overlay_ioctl(struct drm_device *dev, void *data,
 
 	ret = vmw_overlay_update_stream(dev_priv, buf, arg, true);
 
-	vmw_bo_unreference(&buf);
-	drm_gem_object_put(&buf->tbo.base);
+	vmw_user_bo_unref(buf);
 
 out_unlock:
 	mutex_unlock(&overlay->mutex);
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
index e7226db8b242..1e81ff2422cf 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
@@ -809,8 +809,7 @@ static int vmw_shader_define(struct drm_device *dev, struct drm_file *file_priv,
 				    shader_type, num_input_sig,
 				    num_output_sig, tfile, shader_handle);
 out_bad_arg:
-	vmw_bo_unreference(&buffer);
-	drm_gem_object_put(&buffer->tbo.base);
+	vmw_user_bo_unref(buffer);
 	return ret;
 }
 
-- 
2.39.2