drm/amd/display: Fix null check for pipe_ctx->plane_state in hwss_setup_dpp

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Fix null check for pipe_ctx->plane_state in hwss_setup_dpp This commit addresses a null pointer dereference issue in hwss_setup_dpp(). The issue could occur when pipe_ctx->plane_state is null. The fix adds a check to ensure `pipe_ctx->plane_state` is not null before accessing. This prevents a null pointer dereference.

References

• https://git.kernel.org/stable/c/020002c76147ecfdafe95c44abd3240e216b6316
• https://git.kernel.org/stable/c/0dd3d1de7a5957804ccd58c1b252f9e34710e3f6
• https://git.kernel.org/stable/c/95792a18da0795300e15075ac05d1915e9066999
• https://git.kernel.org/stable/c/2bc96c95070571c6c824e0d4c7783bee25a37876