TOMOYO: Allow domain transition without execve().

To be able to split permissions for Apache's CGI programs which are executed
without execve(), add special domain transition which is performed by writing
a TOMOYO's domainname to /sys/kernel/security/tomoyo/self_domain interface.

This is an API for TOMOYO-aware userland applications. However, since I expect
TOMOYO and other LSM modules to run in parallel, this patch does not use
/proc/self/attr/ interface in order to avoid conflicts with other LSM modules
when it became possible to run multiple LSM modules in parallel.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 120 insertions, 2 deletions

diff --git a/security/tomoyo/securityfs_if.c b/security/tomoyo/securityfs_if.c
index a49c3bfd4dd..d08296a4882 100644
--- a/security/tomoyo/securityfs_if.c
+++ b/security/tomoyo/securityfs_if.c
@@ -8,6 +8,124 @@
 #include "common.h"
 
 /**
+ * tomoyo_check_task_acl - Check permission for task operation.
+ *
+ * @r:   Pointer to "struct tomoyo_request_info".
+ * @ptr: Pointer to "struct tomoyo_acl_info".
+ *
+ * Returns true if granted, false otherwise.
+ */
+static bool tomoyo_check_task_acl(struct tomoyo_request_info *r,
+				  const struct tomoyo_acl_info *ptr)
+{
+	const struct tomoyo_task_acl *acl = container_of(ptr, typeof(*acl),
+							 head);
+	return !tomoyo_pathcmp(r->param.task.domainname, acl->domainname);
+}
+
+/**
+ * tomoyo_write_self - write() for /sys/kernel/security/tomoyo/self_domain interface.
+ *
+ * @file:  Pointer to "struct file".
+ * @buf:   Domainname to transit to.
+ * @count: Size of @buf.
+ * @ppos:  Unused.
+ *
+ * Returns @count on success, negative value otherwise.
+ *
+ * If domain transition was permitted but the domain transition failed, this
+ * function returns error rather than terminating current thread with SIGKILL.
+ */
+static ssize_t tomoyo_write_self(struct file *file, const char __user *buf,
+			      size_t count, loff_t *ppos)
+{
+	char *data;
+	int error;
+	if (!count || count >= TOMOYO_EXEC_TMPSIZE - 10)
+		return -ENOMEM;
+	data = kzalloc(count + 1, GFP_NOFS);
+	if (!data)
+		return -ENOMEM;
+	if (copy_from_user(data, buf, count)) {
+		error = -EFAULT;
+		goto out;
+	}
+	tomoyo_normalize_line(data);
+	if (tomoyo_correct_domain(data)) {
+		const int idx = tomoyo_read_lock();
+		struct tomoyo_path_info name;
+		struct tomoyo_request_info r;
+		name.name = data;
+		tomoyo_fill_path_info(&name);
+		/* Check "task manual_domain_transition" permission. */
+		tomoyo_init_request_info(&r, NULL, TOMOYO_MAC_FILE_EXECUTE);
+		r.param_type = TOMOYO_TYPE_MANUAL_TASK_ACL;
+		r.param.task.domainname = &name;
+		tomoyo_check_acl(&r, tomoyo_check_task_acl);
+		if (!r.granted)
+			error = -EPERM;
+		else {
+			struct tomoyo_domain_info *new_domain =
+				tomoyo_assign_domain(data, true);
+			if (!new_domain) {
+				error = -ENOENT;
+			} else {
+				struct cred *cred = prepare_creds();
+				if (!cred) {
+					error = -ENOMEM;
+				} else {
+					struct tomoyo_domain_info *old_domain =
+						cred->security;
+					cred->security = new_domain;
+					atomic_inc(&new_domain->users);
+					atomic_dec(&old_domain->users);
+					commit_creds(cred);
+					error = 0;
+				}
+			}
+		}
+		tomoyo_read_unlock(idx);
+	} else
+		error = -EINVAL;
+out:
+	kfree(data);
+	return error ? error : count;
+}
+
+/**
+ * tomoyo_read_self - read() for /sys/kernel/security/tomoyo/self_domain interface.
+ *
+ * @file:  Pointer to "struct file".
+ * @buf:   Domainname which current thread belongs to.
+ * @count: Size of @buf.
+ * @ppos:  Bytes read by now.
+ *
+ * Returns read size on success, negative value otherwise.
+ */
+static ssize_t tomoyo_read_self(struct file *file, char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	const char *domain = tomoyo_domain()->domainname->name;
+	loff_t len = strlen(domain);
+	loff_t pos = *ppos;
+	if (pos >= len || !count)
+		return 0;
+	len -= pos;
+	if (count < len)
+		len = count;
+	if (copy_to_user(buf, domain + pos, len))
+		return -EFAULT;
+	*ppos += len;
+	return len;
+}
+
+/* Operations for /sys/kernel/security/tomoyo/self_domain interface. */
+static const struct file_operations tomoyo_self_operations = {
+	.write = tomoyo_write_self,
+	.read  = tomoyo_read_self,
+};
+
+/**
  * tomoyo_open - open() for /sys/kernel/security/tomoyo/ interface.
  *
  * @inode: Pointer to "struct inode".
@@ -135,8 +253,6 @@ static int __init tomoyo_initerface_init(void)
 			    TOMOYO_EXCEPTIONPOLICY);
 	tomoyo_create_entry("audit",            0400, tomoyo_dir,
 			    TOMOYO_AUDIT);
-	tomoyo_create_entry("self_domain",      0400, tomoyo_dir,
-			    TOMOYO_SELFDOMAIN);
 	tomoyo_create_entry(".process_status",  0600, tomoyo_dir,
 			    TOMOYO_PROCESS_STATUS);
 	tomoyo_create_entry("stat",             0644, tomoyo_dir,
@@ -147,6 +263,8 @@ static int __init tomoyo_initerface_init(void)
 			    TOMOYO_MANAGER);
 	tomoyo_create_entry("version",          0400, tomoyo_dir,
 			    TOMOYO_VERSION);
+	securityfs_create_file("self_domain", 0666, tomoyo_dir, NULL,
+			       &tomoyo_self_operations);
 	return 0;
 }