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    Subject[PATCH 5.5 41/80] drm/mst: Fix possible NULL pointer dereference in drm_dp_mst_process_up_req()
    Date
    From: José Roberto de Souza <jose.souza@intel.com>

    commit 8ccb5bf7619c6523e7a4384a84b72e7be804298c upstream.

    According to DP specification, DP_SINK_EVENT_NOTIFY is also a
    broadcast message but as this function only handles
    DP_CONNECTION_STATUS_NOTIFY I will only make the static
    analyzer that caught this issue happy by not calling
    drm_dp_get_mst_branch_device_by_guid() with a NULL guid, causing
    drm_dp_mst_process_up_req() to return in the "if (!mstb)" right
    bellow.

    Fixes: 9408cc94eb04 ("drm/dp_mst: Handle UP requests asynchronously")
    Cc: Lyude Paul <lyude@redhat.com>
    Cc: Sean Paul <sean@poorly.run>
    Cc: <stable@vger.kernel.org> # v5.5+
    Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
    [added cc to stable]
    Signed-off-by: Lyude Paul <lyude@redhat.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20200129232448.84704-1-jose.souza@intel.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/drm_dp_mst_topology.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/gpu/drm/drm_dp_mst_topology.c
    +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
    @@ -3772,7 +3772,8 @@ drm_dp_mst_process_up_req(struct drm_dp_
    else if (msg->req_type == DP_RESOURCE_STATUS_NOTIFY)
    guid = msg->u.resource_stat.guid;

    - mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
    + if (guid)
    + mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
    } else {
    mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
    }

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