[PATCH] drm/vmwgfx: Fix possible null pointer derefence with invalid contexts

[Zack Rusin]

vmw_context_cotable can return either an error or a null pointer and its
usage sometimes went unchecked. Subsequent code would then try to access
either a null pointer or an error value.

The invalid dereferences were only possible with malformed userspace
apps which never properly initialized the rendering contexts.

Check the results of vmw_context_cotable to fix the invalid derefs.

Thanks:
ziming zhang(@ezrak1e) from Ant Group Light-Year Security Lab
who was the first person to discover it.
Niels De Graef who reported it and helped to track down the poc.

Fixes: 9c079b8ce8bf ("drm/vmwgfx: Adapt execbuf to the new validation api")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.20+
Reported-by: Niels De Graef  <ndegraef@xxxxxxxxxx>
Signed-off-by: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
Cc: Martin Krastev <martin.krastev@xxxxxxxxxxxx>
Cc: Maaz Mombasawala <maaz.mombasawala@xxxxxxxxxxxx>
Cc: Ian Forbes <ian.forbes@xxxxxxxxxxxx>
Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Maaz Mombasawala <maaz.mombasawala@xxxxxxxxxxxx>
Reviewed-by: Martin Krastev <martin.krastev@xxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20240110200305.94086-1-zack.rusin@xxxxxxxxxxxx
---
 drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index 4c22fe7ec79b7..cc3086e649eb5 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -447,7 +447,7 @@ static int vmw_resource_context_res_add(struct vmw_private *dev_priv,
 	    vmw_res_type(ctx) == vmw_res_dx_context) {
 		for (i = 0; i < cotable_max; ++i) {
 			res = vmw_context_cotable(ctx, i);
-			if (IS_ERR(res))
+			if (IS_ERR_OR_NULL(res))
 				continue;
 
 			ret = vmw_execbuf_res_val_add(sw_context, res,
@@ -1266,6 +1266,8 @@ static int vmw_cmd_dx_define_query(struct vmw_private *dev_priv,
 		return -EINVAL;
 
 	cotable_res = vmw_context_cotable(ctx_node->ctx, SVGA_COTABLE_DXQUERY);
+	if (IS_ERR_OR_NULL(cotable_res))
+		return cotable_res ? PTR_ERR(cotable_res) : -EINVAL;
 	ret = vmw_cotable_notify(cotable_res, cmd->body.queryId);
 
 	return ret;
@@ -2484,6 +2486,8 @@ static int vmw_cmd_dx_view_define(struct vmw_private *dev_priv,
 		return ret;
 
 	res = vmw_context_cotable(ctx_node->ctx, vmw_view_cotables[view_type]);
+	if (IS_ERR_OR_NULL(res))
+		return res ? PTR_ERR(res) : -EINVAL;
 	ret = vmw_cotable_notify(res, cmd->defined_id);
 	if (unlikely(ret != 0))
 		return ret;
@@ -2569,8 +2573,8 @@ static int vmw_cmd_dx_so_define(struct vmw_private *dev_priv,
 
 	so_type = vmw_so_cmd_to_type(header->id);
 	res = vmw_context_cotable(ctx_node->ctx, vmw_so_cotables[so_type]);
-	if (IS_ERR(res))
-		return PTR_ERR(res);
+	if (IS_ERR_OR_NULL(res))
+		return res ? PTR_ERR(res) : -EINVAL;
 	cmd = container_of(header, typeof(*cmd), header);
 	ret = vmw_cotable_notify(res, cmd->defined_id);
 
@@ -2689,6 +2693,8 @@ static int vmw_cmd_dx_define_shader(struct vmw_private *dev_priv,
 		return -EINVAL;
 
 	res = vmw_context_cotable(ctx_node->ctx, SVGA_COTABLE_DXSHADER);
+	if (IS_ERR_OR_NULL(res))
+		return res ? PTR_ERR(res) : -EINVAL;
 	ret = vmw_cotable_notify(res, cmd->body.shaderId);
 	if (ret)
 		return ret;
@@ -3010,6 +3016,8 @@ static int vmw_cmd_dx_define_streamoutput(struct vmw_private *dev_priv,
 	}
 
 	res = vmw_context_cotable(ctx_node->ctx, SVGA_COTABLE_STREAMOUTPUT);
+	if (IS_ERR_OR_NULL(res))
+		return res ? PTR_ERR(res) : -EINVAL;
 	ret = vmw_cotable_notify(res, cmd->body.soid);
 	if (ret)
 		return ret;
-- 
2.43.0