drm/amd/display: Fix a NULL pointer dereference in amdgpu_dm_connector_add_common_modes()

stable inclusion
from stable-v5.10.110
commit 19a7eba284790cfbba2945deb2363cf03ce41648
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=19a7eba284790cfbba2945deb2363cf03ce41648

--------------------------------

[ Upstream commit 588a7017 ]

In amdgpu_dm_connector_add_common_modes(), amdgpu_dm_create_common_mode()
is assigned to mode and is passed to drm_mode_probed_add() directly after
that. drm_mode_probed_add() passes &mode->head to list_add_tail(), and
there is a dereference of it in list_add_tail() without recoveries, which
could lead to NULL pointer dereference on failure of
amdgpu_dm_create_common_mode().

Fix this by adding a NULL check of mode.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: e7b07cee ("drm/amd/display: Merge amdgpu_dm_types and amdgpu_dm")
Signed-off-by: NZhou Qingyang <zhou1615@umn.edu>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -6396,6 +6396,9 @@ static void amdgpu_dm_connector_add_common_modes(struct drm_encoder *encoder,
 		mode = amdgpu_dm_create_common_mode(encoder,
 				common_modes[i].name, common_modes[i].w,
 				common_modes[i].h);
+		if (!mode)
+			continue;
+
 		drm_mode_probed_add(connector, mode);
 		amdgpu_dm_connector->num_modes++;
 	}