drm/vmwgfx: avoid null pointer dereference at failure paths

vmw_takedown_otable_base() and vmw_mob_unbind() check for
potential vmw_fifo_reserve() failure and print error message,
but then immediately dereference NULL pointer.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>

1 files changed, 19 insertions, 16 deletions

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c b/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
index d4a5a19cb8c3..04a64b8cd3cd 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
@@ -188,18 +188,20 @@ static void vmw_takedown_otable_base(struct vmw_private *dev_priv,
 
         bo = otable->page_table->pt_bo;
         cmd = vmw_fifo_reserve(dev_priv, sizeof(*cmd));
-        if (unlikely(cmd == NULL))
-                DRM_ERROR("Failed reserving FIFO space for OTable setup.\n");
-
-        memset(cmd, 0, sizeof(*cmd));
-        cmd->header.id = SVGA_3D_CMD_SET_OTABLE_BASE;
-        cmd->header.size = sizeof(cmd->body);
-        cmd->body.type = type;
-        cmd->body.baseAddress = 0;
-        cmd->body.sizeInBytes = 0;
-        cmd->body.validSizeInBytes = 0;
-        cmd->body.ptDepth = SVGA3D_MOBFMT_INVALID;
-        vmw_fifo_commit(dev_priv, sizeof(*cmd));
+        if (unlikely(cmd == NULL)) {
+                DRM_ERROR("Failed reserving FIFO space for OTable "
+                          "takedown.\n");
+        } else {
+                memset(cmd, 0, sizeof(*cmd));
+                cmd->header.id = SVGA_3D_CMD_SET_OTABLE_BASE;
+                cmd->header.size = sizeof(cmd->body);
+                cmd->body.type = type;
+                cmd->body.baseAddress = 0;
+                cmd->body.sizeInBytes = 0;
+                cmd->body.validSizeInBytes = 0;
+                cmd->body.ptDepth = SVGA3D_MOBFMT_INVALID;
+                vmw_fifo_commit(dev_priv, sizeof(*cmd));
+        }
 
         if (bo) {
                 int ret;
@@ -562,11 +564,12 @@ void vmw_mob_unbind(struct vmw_private *dev_priv,
         if (unlikely(cmd == NULL)) {
                 DRM_ERROR("Failed reserving FIFO space for Memory "
                           "Object unbinding.\n");
+        } else {
+                cmd->header.id = SVGA_3D_CMD_DESTROY_GB_MOB;
+                cmd->header.size = sizeof(cmd->body);
+                cmd->body.mobid = mob->id;
+                vmw_fifo_commit(dev_priv, sizeof(*cmd));
         }
-        cmd->header.id = SVGA_3D_CMD_DESTROY_GB_MOB;
-        cmd->header.size = sizeof(cmd->body);
-        cmd->body.mobid = mob->id;
-        vmw_fifo_commit(dev_priv, sizeof(*cmd));
         if (bo) {
                 vmw_fence_single_bo(bo, NULL);
                 ttm_bo_unreserve(bo);