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

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Fix a NULL pointer dereference in amdgpu_dm_connector_add_common_modes() 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.

References

• https://git.kernel.org/stable/c/2c729dec8c1e3e2892fde5ce8181553860914e74
• https://git.kernel.org/stable/c/57f4ad5e286fe4599c8fc63cf89f85f9eec7f9c9
• https://git.kernel.org/stable/c/19a7eba284790cfbba2945deb2363cf03ce41648
• https://git.kernel.org/stable/c/bdc7429708a0772d90c208975694f7c2133b1202
• https://git.kernel.org/stable/c/f4eaa999fec78dec2a9c2d797438e05cbffb125b
• https://git.kernel.org/stable/c/639b3b9def0a6a3f316a195d705d14113236e89c
• https://git.kernel.org/stable/c/588a70177df3b1777484267584ef38ab2ca899a2