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    Subject[PATCH 5.7 201/204] drm: fix drm_dp_mst_port refcount leaks in drm_dp_mst_allocate_vcpi
    Date
    From: Xin Xiong <xiongx18@fudan.edu.cn>

    commit a34a0a632dd991a371fec56431d73279f9c54029 upstream.

    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
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/drm_dp_mst_topology.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/drivers/gpu/drm/drm_dp_mst_topology.c
    +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
    @@ -4319,11 +4319,11 @@ bool drm_dp_mst_allocate_vcpi(struct drm
    {
    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) {
    @@ -4339,6 +4339,7 @@ bool drm_dp_mst_allocate_vcpi(struct drm
    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",

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