[PATCH 4.14.y] drm/client: Fix memory leak in drm_client_target_cloned

[Jocelyn Falempe <jfalempe@redhat.com>]

dmt_mode is allocated and never freed in this function.
It was found with the ast driver, but most drivers using generic fbdev
setup are probably affected.

This fixes the following kmemleak report:
  backtrace:
    [<00000000b391296d>] drm_mode_duplicate+0x45/0x220 [drm]
    [<00000000e45bb5b3>] drm_client_target_cloned.constprop.0+0x27b/0x480 [drm]
    [<00000000ed2d3a37>] drm_client_modeset_probe+0x6bd/0xf50 [drm]
    [<0000000010e5cc9d>] __drm_fb_helper_initial_config_and_unlock+0xb4/0x2c0 [drm_kms_helper]
    [<00000000909f82ca>] drm_fbdev_client_hotplug+0x2bc/0x4d0 [drm_kms_helper]
    [<00000000063a69aa>] drm_client_register+0x169/0x240 [drm]
    [<00000000a8c61525>] ast_pci_probe+0x142/0x190 [ast]
    [<00000000987f19bb>] local_pci_probe+0xdc/0x180
    [<000000004fca231b>] work_for_cpu_fn+0x4e/0xa0
    [<0000000000b85301>] process_one_work+0x8b7/0x1540
    [<000000003375b17c>] worker_thread+0x70a/0xed0
    [<00000000b0d43cd9>] kthread+0x29f/0x340
    [<000000008d770833>] ret_from_fork+0x1f/0x30
unreferenced object 0xff11000333089a00 (size 128):

cc: <stable@vger.kernel.org>
Fixes: 1d42bbc8f7f9 ("drm/fbdev: fix cloning on fbcon")
Reported-by: Zhang Yi <yizhan@redhat.com>
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230711092203.68157-2-jfalempe@redhat.com
(cherry picked from commit c2a88e8bdf5f6239948d75283d0ae7e0c7945b03)
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index fbf7f28d9df9..e8d0dbe92048 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -2112,6 +2112,9 @@ static bool drm_target_cloned(struct drm_fb_helper *fb_helper,
 	can_clone = true;
 	dmt_mode = drm_mode_find_dmt(fb_helper->dev, 1024, 768, 60, false);
 
+	if (!dmt_mode)
+		goto fail;
+
 	drm_fb_helper_for_each_connector(fb_helper, i) {
 		if (!enabled[i])
 			continue;
@@ -2124,11 +2127,13 @@ static bool drm_target_cloned(struct drm_fb_helper *fb_helper,
 		if (!modes[i])
 			can_clone = false;
 	}
+	kfree(dmt_mode);
 
 	if (can_clone) {
 		DRM_DEBUG_KMS("can clone using 1024x768\n");
 		return true;
 	}
+fail:
 	DRM_INFO("kms: can't enable cloning when we probably wanted to.\n");
 	return false;
 }
-- 
2.41.0