ueventd: allow reading kernel cmdline

This is needed when ueventd needs to read device tree files
(/proc/device-tree). Prior to acccess, it tries to read
"androidboot.android_dt_dir" from kernel cmdline for a custom
Android DT path.

Bug: 78613232
Test: boot a device without unknown SELinux denials
Change-Id: Iff9c882b4fcad5e384757a1e42e4a1d1259bb574

public/ueventd.te

@@ -36,6 +36,9 @@ allow ueventd file_contexts_file:file r_file_perms;
 # Use setfscreatecon() to label /dev directories and files.
 allow ueventd self:process setfscreate;
 
+# Allow ueventd to read androidboot.android_dt_dir from kernel cmdline.
+allow ueventd proc_cmdline:file r_file_perms;
+
 #####
 ##### neverallow rules
 #####