The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a34a0a632dd991a371fec56431d73279f9c54029 Mon Sep 17 00:00:00 2001

From: Xin Xiong xiongx18@fudan.edu.cn Date: Sun, 19 Jul 2020 23:45:45 +0800 Subject: [PATCH] drm: fix drm_dp_mst_port refcount leaks in drm_dp_mst_allocate_vcpi MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

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-vir...

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 09b32289497e..b23cb2fec3f3 100644 --- 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",