cmdline

system/core/init/selinux.cpp

StatusFromCmdline 從cmdline獲取selinux資訊：

EnforcingStatus StatusFromCmdline() {
    EnforcingStatus status = SELINUX_ENFORCING;

    ImportKernelCmdline([&](const std::string& key, const std::string& value) {
        if (key == "androidboot.selinux"
 
 && value == "permissive") {
            status = SELINUX_PERMISSIVE;
        }
    });

    return status;
}

bool IsEnforcing() {
    if (ALLOW_PERMISSIVE_SELINUX) {
        return StatusFromCmdline() == SELINUX_ENFORCING;
    }
    return true;
}

SelinuxInitialize selinux初始化，呼叫security_setenforce方法設定selinux狀態

void SelinuxInitialize() {
    LOG(INFO) << "Loading SELinux policy";
    if (!LoadPolicy()) {
        LOG(FATAL) << "Unable to load SELinux policy";
    }

    bool kernel_enforcing = (security_getenforce() == 1);
    bool is_enforcing = IsEnforcing();
    if (kernel_enforcing !=
 
 is_enforcing) {
        if (security_setenforce(is_enforcing)) {
            PLOG(FATAL) << "security_setenforce(" << (is_enforcing ? "true" : "false")
                        << ") failed";
        }
    }

    if (auto result = WriteFile("/sys/fs/selinux/checkreqprot", "0"); !result.ok()) {
        LOG(FATAL) << "Unable to write to /sys/fs/selinux/checkreqprot: " << result.error();
    }
}

external/selinux/libselinux/src/setenforce.c

selinux_mnt 節點：

• external/selinux/libselinux/src/policy.h:24:#define SELINUXMNT “/sys/fs/selinux”
• external/selinux/libselinux/src/policy.h:25:#define OLDSELINUXMNT “/selinux”

int security_setenforce(int value)
{
	int fd, ret;
	char path[PATH_MAX];
	char buf[20];

	if (!selinux_mnt) {
		errno = ENOENT;
		return -1;
	}

	snprintf(path, sizeof path, "%s/enforce", selinux_mnt);
	fd = open(path, O_RDWR | O_CLOEXEC);
	if (fd < 0)
		return -1;

	snprintf(buf, sizeof buf, "%d", value);
	ret = write(fd, buf, strlen(buf));
	close(fd);
	if (ret < 0)
		return -1;

	return 0;
}

通過write()方法在enforce節點寫入對應的值，改變selinux狀態。

節點

selinux相關節點：

節點建立檔案:

kernel/security/selinux/selinuxfs.c

static int sel_fill_super(struct super_block *sb, struct fs_context *fc)
{
	struct selinux_fs_info *fsi;
	int ret;
	struct dentry *dentry;
	struct inode *inode;
	struct inode_security_struct *isec;

	static const struct tree_descr selinux_files[] = {
		[SEL_LOAD] = {"load", &sel_load_ops, S_IRUSR|S_IWUSR},
		[SEL_ENFORCE] = {"enforce", &sel_enforce_ops, S_IRUGO|S_IWUSR},
		[SEL_CONTEXT] = {"context", &transaction_ops, S_IRUGO|S_IWUGO},
		[SEL_ACCESS] = {"access", &transaction_ops, S_IRUGO|S_IWUGO},
		[SEL_CREATE] = {"create", &transaction_ops, S_IRUGO|S_IWUGO},
		[SEL_RELABEL] = {"relabel", &transaction_ops, S_IRUGO|S_IWUGO},
		[SEL_USER] = {"user", &transaction_ops, S_IRUGO|S_IWUGO},
		[SEL_POLICYVERS] = {"policyvers", &sel_policyvers_ops, S_IRUGO},
		[SEL_COMMIT_BOOLS] = {"commit_pending_bools", &sel_commit_bools_ops, S_IWUSR},
		[SEL_MLS] = {"mls", &sel_mls_ops, S_IRUGO},
		[SEL_DISABLE] = {"disable", &sel_disable_ops, S_IWUSR},
		[SEL_MEMBER] = {"member", &transaction_ops, S_IRUGO|S_IWUGO},
		[SEL_CHECKREQPROT] = {"checkreqprot", &sel_checkreqprot_ops, S_IRUGO|S_IWUSR},
		[SEL_REJECT_UNKNOWN] = {"reject_unknown", &sel_handle_unknown_ops, S_IRUGO},
		[SEL_DENY_UNKNOWN] = {"deny_unknown", &sel_handle_unknown_ops, S_IRUGO},
		[SEL_STATUS] = {"status", &sel_handle_status_ops, S_IRUGO},
		[SEL_POLICY] = {"policy", &sel_policy_ops, S_IRUGO},
		[SEL_VALIDATE_TRANS] = {"validatetrans", &sel_transition_ops,
					S_IWUGO},
		/* last one */ {""}
	};
	...
	...

檢視 enforce節點的 write 方法 sel_write_enforce():

static ssize_t sel_write_enforce(struct file *file, const char __user *buf,
				 size_t count, loff_t *ppos)

{
	struct selinux_fs_info *fsi = file_inode(file)->i_sb->s_fs_info;
	struct selinux_state *state = fsi->state;
	...
	if (new_value != old_value) {
		...
		enforcing_set(state, new_value);
		...
	}
	length = count;
out:
	kfree(page);
	return length;
}

呼叫了 enforcing_set(state, new_value)方法，同樣也是在enforce節點寫入對應值。

kernel/security/selinux/include/secruity.h

static inline void enforcing_set(struct selinux_state *state, bool value)
{
	state->enforcing = value;
}