kernel: safe and small changes for UL support

Safe Ultra-Legacy changes that don't deserve their own commit

d_is_reg requires 4.0
 - torvalds/linux@e36cb0b
IS_REG is still there on 6.15 so I do NOT see any issues forcing it for all.

strscpy requires 4.3
strscpy on this usage can be replaced with strncpy + null term.
kernel gives us an option though.
strlcpy is fast af, hotrod fast. It’s just memcpy + null term, so lets go with that.
it got dropped in 6.8 due to risk concerns, so for those, lets use og strscpy.
ref: openwrt/packages #26453

cred->session_keyring -> cred->tgcred->session_keyring
ref:
https://elixir.bootlin.com/linux/v3.8/source/include/linux/cred.h
https://elixir.bootlin.com/linux/v3.7/source/include/linux/cred.h

Makefile: remove overlayfs dependency
- not needed with magic mount

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

Author: backslashxx

kernel/Kconfig

@@ -2,7 +2,6 @@ menu "KernelSU"
 
 config KSU
 	bool "KernelSU function support"
-	depends on OVERLAY_FS
 	default y
 	help
 	  Enable kernel-level root privileges on Android System.

kernel/core_hook.c

@@ -703,7 +703,11 @@ LSM_HANDLER_TYPE ksu_key_permission(key_ref_t key_ref, const struct cred *cred,
 		// we are only interested in `init` process
 		return 0;
 	}
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 8, 0)
 	init_session_keyring = cred->session_keyring;
+#else
+	init_session_keyring = cred->tgcred->session_keyring;
+#endif
 	pr_info("kernel_compat: got init_session_keyring\n");
 	return 0;
 }

kernel/kernel_compat.c

@@ -79,7 +79,12 @@ void ksu_android_ns_fs_check()
 struct file *ksu_filp_open_compat(const char *filename, int flags, umode_t mode)
 {
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0) || defined(CONFIG_KSU_ALLOWLIST_WORKAROUND)
-	if (init_session_keyring != NULL && !current_cred()->session_keyring &&
+	if (init_session_keyring != NULL && 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 8, 0)
+	!current_cred()->session_keyring &&
+#else
+	!current_cred()->tgcred->session_keyring &&
+#endif
 	    (current->flags & PF_WQ_WORKER)) {
 		pr_info("installing init session keyring for older kernel\n");
 		install_session_keyring(init_session_keyring);

kernel/ksud.c

@@ -352,7 +352,7 @@ int ksu_handle_vfs_read(struct file **file_ptr, char __user **buf_ptr,
 		return 0;
 	}
 
-	if (!d_is_reg(file->f_path.dentry)) {
+	if (!S_ISREG(file->f_path.dentry->d_inode->i_mode)) {
 		return 0;
 	}
 

kernel/throne_tracker.c

@@ -174,7 +174,11 @@ FILLDIR_RETURN_TYPE my_actor(struct dir_context *ctx, const char *name,
 			return FILLDIR_ACTOR_CONTINUE;
 		}
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 8, 0)
+		strlcpy(data->dirpath, dirpath, DATA_PATH_LEN);
+#else
 		strscpy(data->dirpath, dirpath, DATA_PATH_LEN);
+#endif
 		data->depth = my_ctx->depth - 1;
 		list_add_tail(&data->list, my_ctx->data_path_list);
 	} else {
@@ -230,7 +234,11 @@ void search_manager(const char *path, int depth, struct list_head *uid_data)
 
 	// First depth
 	struct data_path data;
+#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 8, 0)
+	strlcpy(data.dirpath, path, DATA_PATH_LEN);
+#else
 	strscpy(data.dirpath, path, DATA_PATH_LEN);
+#endif
 	data.depth = depth;
 	list_add_tail(&data.list, &data_path_list);