drm: fix drm_dp_mst_port refcount leaks in drm_dp_mst_allocate_vcpi

drm_dp_mst_allocate_vcpi() invokes
drm_dp_mst_topology_get_port_validated(), which increases the refcount
of the "port".

These reference counting issues take place in two exception handling
paths separately. Either when “slots” is less than 0 or when
drm_dp_init_vcpi() returns a negative value, the function forgets to
reduce the refcnt increased drm_dp_mst_topology_get_port_validated(),
which results in a refcount leak.

Fix these issues by pulling up the error handling when "slots" is less
than 0, and calling drm_dp_mst_topology_put_port() before termination
when drm_dp_init_vcpi() returns a negative value.

Fixes: 1e797f556c61 ("drm/dp: Split drm_dp_mst_allocate_vcpi")
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Signed-off-by: Xin Xiong <xiongx18@fudan.edu.cn>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200719154545.GA41231@xin-virtual-machine

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 09b3228..b23cb2f 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -4308,11 +4308,11 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 {
        int ret;
 
-       port = drm_dp_mst_topology_get_port_validated(mgr, port);
-       if (!port)
+       if (slots < 0)
                return false;
 
-       if (slots < 0)
+       port = drm_dp_mst_topology_get_port_validated(mgr, port);
+       if (!port)
                return false;
 
        if (port->vcpi.vcpi > 0) {
@@ -4328,6 +4328,7 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
        if (ret) {
                DRM_DEBUG_KMS("failed to init vcpi slots=%d max=63 ret=%d\n",
                              DIV_ROUND_UP(pbn, mgr->pbn_div), ret);
+               drm_dp_mst_topology_put_port(port);
                goto out;
        }
        DRM_DEBUG_KMS("initing vcpi for pbn=%d slots=%d\n",