kernel: keep legacy throne tracker as an option

This commit restores older throne tracker that uses packages.list scanning
to track app UIDs. It's intended for ultra-legacy Linux 3.X kernels that
experience deadlocks or crashes with the newer implementation due to issues
in user_data_actor().

We have to remember that the whole iterate_dir, and filldir subsystem is way
different on 3.X.

Changes:
- CONFIG_KSU_THRONE_TRACKER_LEGACY in Kconfig
- conditional compilation in Makefile
- throne_tracker_legacy.c which keeps the old implementation

Enable this option if newer throne tracker (tiann#2757) crashes on you.

Signed-off-by: backslashxx <[email protected]>

Author: backslashxx

kernel/Kconfig

@@ -7,6 +7,15 @@ config KSU
 	help
 	  Enable kernel-level root privileges on Android System.
 
+config KSU_THRONE_TRACKER_LEGACY
+	bool "Use legacy throne tracker (packages.list scanning)"
+	depends on KSU
+	default n
+	help
+	  Use legacy throne tracker that scans packages.list for app UIDs.
+	  This is kept for Ultra-Legacy Linux 3.X kernels which are prone to deadlocks.
+	  Enable this if default scanning deadlocks/crashes on you.
+
 config KSU_DEBUG
 	bool "KernelSU debug mode"
 	depends on KSU

kernel/Makefile

@@ -2,7 +2,6 @@ kernelsu-objs := ksu.o
 kernelsu-objs += allowlist.o
 kernelsu-objs += apk_sign.o
 kernelsu-objs += sucompat.o
-kernelsu-objs += throne_tracker.o
 kernelsu-objs += core_hook.o
 kernelsu-objs += ksud.o
 kernelsu-objs += embed_ksud.o
@@ -11,6 +10,21 @@ kernelsu-objs += kernel_compat.o
 kernelsu-objs += selinux/selinux.o
 kernelsu-objs += selinux/sepolicy.o
 kernelsu-objs += selinux/rules.o
+
+#ifeq ($(shell [ $(VERSION) -lt 4 ] && echo $$?),0)
+#kernelsu-objs += throne_tracker_legacy.o
+#else
+#kernelsu-objs += throne_tracker.o
+#endif
+
+ifeq ($(CONFIG_KSU_THRONE_TRACKER_LEGACY),y)
+$(info -- KernelSU/compat: using legacy throne tracker)
+kernelsu-objs += throne_tracker_legacy.o
+else
+$(info -- KernelSU/compat: using new throne tracker)
+kernelsu-objs += throne_tracker.o
+endif
+
 ccflags-y += -I$(srctree)/security/selinux -I$(srctree)/security/selinux/include
 ccflags-y += -I$(objtree)/security/selinux -include $(srctree)/include/uapi/asm-generic/errno.h