kernel: fix filp_open on older kernel's kworker (#205)

On older kernel, kworker missing keyring from init process , and this
keyring is related to FBE , which causes filp_open return ENOKEY or
other errors.To fix this,just install init's keyring to per
kworkers.This works on Kernel 4.4 and 4.9.

kernel/allowlist.c

@@ -22,12 +22,7 @@ struct perm_data {
 
 static struct list_head allow_list;
 
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 5, 0)
 #define KERNEL_SU_ALLOWLIST "/data/adb/ksu/.allowlist"
-#else
-// filp_open return error if under encryption dir on Kernel4.4
-#define KERNEL_SU_ALLOWLIST "/data/user_de/.ksu_allowlist"
-#endif
 
 static struct work_struct ksu_save_work;
 static struct work_struct ksu_load_work;
@@ -124,7 +119,7 @@ void do_persistent_allow_list(struct work_struct *work)
 	struct perm_data *p = NULL;
 	struct list_head *pos = NULL;
 	loff_t off = 0;
-
+	KWORKER_INSTALL_KEYRING();
 	struct file *fp =
 		filp_open(KERNEL_SU_ALLOWLIST, O_WRONLY | O_CREAT, 0644);
 
@@ -164,7 +159,7 @@ void do_load_allow_list(struct work_struct *work)
 	struct file *fp = NULL;
 	u32 magic;
 	u32 version;
-
+	KWORKER_INSTALL_KEYRING();
 	fp = filp_open("/data/adb", O_RDONLY, 0);
 	if (IS_ERR(fp)) {
 		int errno = PTR_ERR(fp);

kernel/core_hook.c

@@ -22,6 +22,7 @@
 #include "manager.h"
 #include "selinux/selinux.h"
 #include "uid_observer.h"
+#include "kernel_compat.h"
 
 extern int handle_sepolicy(unsigned long arg3, void __user *arg4);
 
@@ -356,7 +357,26 @@ static int ksu_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 	ksu_handle_prctl(option, arg2, arg3, arg4, arg5);
 	return -ENOSYS;
 }
-
+// kernel 4.4 and 4.9
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+static int ksu_key_permission(key_ref_t key_ref,
+				  const struct cred *cred,
+				  unsigned perm)
+{
+	if (init_session_keyring != NULL)
+	{
+		return 0;
+	}
+	if (strcmp(current->comm, "init"))
+	{
+		// we are only interested in `init` process
+		return 0;
+	}
+	init_session_keyring = cred->session_keyring;
+	pr_info("kernel_compat: got init_session_keyring");
+	return 0;
+}
+#endif
 static int ksu_inode_rename(struct inode *old_inode, struct dentry *old_dentry,
 			    struct inode *new_inode, struct dentry *new_dentry)
 {
@@ -366,6 +386,9 @@ static int ksu_inode_rename(struct inode *old_inode, struct dentry *old_dentry,
 static struct security_hook_list ksu_hooks[] = {
 	LSM_HOOK_INIT(task_prctl, ksu_task_prctl),
 	LSM_HOOK_INIT(inode_rename, ksu_inode_rename),
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+	LSM_HOOK_INIT(key_permission, ksu_key_permission)
+#endif
 };
 
 void __init ksu_lsm_hook_init(void)

kernel/kernel_compat.c

@@ -1,6 +1,10 @@
 #include "linux/version.h"
-#include "linux/init.h"
 #include "linux/fs.h"
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+#include "linux/key.h"
+#include "linux/errno.h"
+struct key *init_session_keyring = NULL;
+#endif
 ssize_t kernel_read_compat(struct file *p, void *buf, size_t count, loff_t *pos){
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
     return kernel_read(p, buf, count, pos);

kernel/kernel_compat.h

@@ -2,7 +2,41 @@
 #define __KSU_H_KERNEL_COMPAT
 
 #include "linux/fs.h"
+#include "linux/key.h"
+#include "linux/version.h"
+
+extern struct key *init_session_keyring;
 
 extern ssize_t kernel_read_compat(struct file *p, void *buf, size_t count, loff_t *pos);
 extern ssize_t kernel_write_compat(struct file *p, const void *buf, size_t count, loff_t *pos);
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+static inline int install_session_keyring(struct key *keyring)
+{
+	struct cred *new;
+	int ret;
+
+	new = prepare_creds();
+	if (!new)
+		return -ENOMEM;
+
+	ret = install_session_keyring_to_cred(new, keyring);
+	if (ret < 0) {
+		abort_creds(new);
+		return ret;
+	}
+
+	return commit_creds(new);
+}
+#define KWORKER_INSTALL_KEYRING()                           \
+	static bool keyring_installed = false;                  \
+	if (init_session_keyring != NULL && !keyring_installed) \
+	{                                                       \
+		install_session_keyring(init_session_keyring);      \
+		keyring_installed = true;                           \
+	}
+#else
+#define KWORKER_INSTALL_KEYRING()
+#endif
+
 #endif

kernel/uid_observer.c

@@ -39,6 +39,7 @@ static bool is_uid_exist(uid_t uid, void *data)
 
 static void do_update_uid(struct work_struct *work)
 {
+	KWORKER_INSTALL_KEYRING();
 	struct file *fp = filp_open(SYSTEM_PACKAGES_LIST_PATH, O_RDONLY, 0);
 	if (IS_ERR(fp)) {
 		pr_err("do_update_uid, open " SYSTEM_PACKAGES_LIST_PATH