eCryptfs: Make all miscdev functions use daemon ptr in file private_data

Now that a pointer to a valid struct ecryptfs_daemon is stored in the
private_data of an opened /dev/ecryptfs file, the remaining miscdev
functions can utilize the pointer rather than looking up the
ecryptfs_daemon at the beginning of each operation.

The security model of /dev/ecryptfs is simplified a little bit with this
patch. Upon opening /dev/ecryptfs, a per-user ecryptfs_daemon is
registered. Another daemon cannot be registered for that user until the
last file reference is released. During the lifetime of the
ecryptfs_daemon, access checks are not performed on the /dev/ecryptfs
operations because it is assumed that the application securely handles
the opened file descriptor and does not unintentionally leak it to
processes that are not trusted.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Cc: Sasha Levin <levinsasha928@gmail.com>

fs/ecryptfs/messaging.c

@@ -32,8 +32,8 @@ static struct mutex ecryptfs_msg_ctx_lists_mux;
 static struct hlist_head *ecryptfs_daemon_hash;
 struct mutex ecryptfs_daemon_hash_mux;
 static int ecryptfs_hash_bits;
-#define ecryptfs_uid_hash(uid) \
-        hash_long((unsigned long)uid, ecryptfs_hash_bits)
+#define ecryptfs_current_euid_hash(uid) \
+		hash_long((unsigned long)current_euid(), ecryptfs_hash_bits)
 
 static u32 ecryptfs_msg_counter;
 static struct ecryptfs_msg_ctx *ecryptfs_msg_ctx_arr;
@@ -105,26 +105,24 @@ void ecryptfs_msg_ctx_alloc_to_free(struct ecryptfs_msg_ctx *msg_ctx)
 
 /**
  * ecryptfs_find_daemon_by_euid
- * @euid: The effective user id which maps to the desired daemon id
- * @user_ns: The namespace in which @euid applies
  * @daemon: If return value is zero, points to the desired daemon pointer
  *
  * Must be called with ecryptfs_daemon_hash_mux held.
  *
- * Search the hash list for the given user id.
+ * Search the hash list for the current effective user id.
  *
  * Returns zero if the user id exists in the list; non-zero otherwise.
  */
-int ecryptfs_find_daemon_by_euid(struct ecryptfs_daemon **daemon, uid_t euid,
-				 struct user_namespace *user_ns)
+int ecryptfs_find_daemon_by_euid(struct ecryptfs_daemon **daemon)
 {
 	struct hlist_node *elem;
 	int rc;
 
 	hlist_for_each_entry(*daemon, elem,
-			     &ecryptfs_daemon_hash[ecryptfs_uid_hash(euid)],
-			     euid_chain) {
-		if ((*daemon)->euid == euid && (*daemon)->user_ns == user_ns) {
+			    &ecryptfs_daemon_hash[ecryptfs_current_euid_hash()],
+			    euid_chain) {
+		if ((*daemon)->file->f_cred->euid == current_euid() &&
+		    (*daemon)->file->f_cred->user_ns == current_user_ns()) {
 			rc = 0;
 			goto out;
 		}
@@ -137,9 +135,7 @@ out:
 /**
  * ecryptfs_spawn_daemon - Create and initialize a new daemon struct
  * @daemon: Pointer to set to newly allocated daemon struct
- * @euid: Effective user id for the daemon
- * @user_ns: The namespace in which @euid applies
- * @pid: Process id for the daemon
+ * @file: File used when opening /dev/ecryptfs
  *
  * Must be called ceremoniously while in possession of
  * ecryptfs_sacred_daemon_hash_mux
@@ -147,8 +143,7 @@ out:
  * Returns zero on success; non-zero otherwise
  */
 int
-ecryptfs_spawn_daemon(struct ecryptfs_daemon **daemon, uid_t euid,
-		      struct user_namespace *user_ns, struct pid *pid)
+ecryptfs_spawn_daemon(struct ecryptfs_daemon **daemon, struct file *file)
 {
 	int rc = 0;
 
@@ -159,16 +154,13 @@ ecryptfs_spawn_daemon(struct ecryptfs_daemon **daemon, uid_t euid,
 		       "GFP_KERNEL memory\n", __func__, sizeof(**daemon));
 		goto out;
 	}
-	(*daemon)->euid = euid;
-	(*daemon)->user_ns = get_user_ns(user_ns);
-	(*daemon)->pid = get_pid(pid);
-	(*daemon)->task = current;
+	(*daemon)->file = file;
 	mutex_init(&(*daemon)->mux);
 	INIT_LIST_HEAD(&(*daemon)->msg_ctx_out_queue);
 	init_waitqueue_head(&(*daemon)->wait);
 	(*daemon)->num_queued_msg_ctx = 0;
 	hlist_add_head(&(*daemon)->euid_chain,
-		       &ecryptfs_daemon_hash[ecryptfs_uid_hash(euid)]);
+		       &ecryptfs_daemon_hash[ecryptfs_current_euid_hash()]);
 out:
 	return rc;
 }
@@ -188,9 +180,6 @@ int ecryptfs_exorcise_daemon(struct ecryptfs_daemon *daemon)
 	if ((daemon->flags & ECRYPTFS_DAEMON_IN_READ)
 	    || (daemon->flags & ECRYPTFS_DAEMON_IN_POLL)) {
 		rc = -EBUSY;
-		printk(KERN_WARNING "%s: Attempt to destroy daemon with pid "
-		       "[0x%p], but it is in the midst of a read or a poll\n",
-		       __func__, daemon->pid);
 		mutex_unlock(&daemon->mux);
 		goto out;
 	}
@@ -203,12 +192,6 @@ int ecryptfs_exorcise_daemon(struct ecryptfs_daemon *daemon)
 		ecryptfs_msg_ctx_alloc_to_free(msg_ctx);
 	}
 	hlist_del(&daemon->euid_chain);
-	if (daemon->task)
-		wake_up_process(daemon->task);
-	if (daemon->pid)
-		put_pid(daemon->pid);
-	if (daemon->user_ns)
-		put_user_ns(daemon->user_ns);
 	mutex_unlock(&daemon->mux);
 	kzfree(daemon);
 out:
@@ -219,8 +202,6 @@ out:
  * ecryptfs_process_reponse
  * @msg: The ecryptfs message received; the caller should sanity check
  *       msg->data_len and free the memory
- * @pid: The process ID of the userspace application that sent the
- *       message
  * @seq: The sequence number of the message; must match the sequence
  *       number for the existing message context waiting for this
  *       response
@@ -239,16 +220,11 @@ out:
  *
  * Returns zero on success; non-zero otherwise
  */
-int ecryptfs_process_response(struct ecryptfs_message *msg, uid_t euid,
-			      struct user_namespace *user_ns, struct pid *pid,
-			      u32 seq)
+int ecryptfs_process_response(struct ecryptfs_daemon *daemon,
+			      struct ecryptfs_message *msg, u32 seq)
 {
-	struct ecryptfs_daemon *uninitialized_var(daemon);
 	struct ecryptfs_msg_ctx *msg_ctx;
 	size_t msg_size;
-	struct nsproxy *nsproxy;
-	struct user_namespace *tsk_user_ns;
-	uid_t ctx_euid;
 	int rc;
 
 	if (msg->index >= ecryptfs_message_buf_len) {
@@ -261,51 +237,6 @@ int ecryptfs_process_response(struct ecryptfs_message *msg, uid_t euid,
 	}
 	msg_ctx = &ecryptfs_msg_ctx_arr[msg->index];
 	mutex_lock(&msg_ctx->mux);
-	mutex_lock(&ecryptfs_daemon_hash_mux);
-	rcu_read_lock();
-	nsproxy = task_nsproxy(msg_ctx->task);
-	if (nsproxy == NULL) {
-		rc = -EBADMSG;
-		printk(KERN_ERR "%s: Receiving process is a zombie. Dropping "
-		       "message.\n", __func__);
-		rcu_read_unlock();
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
-		goto wake_up;
-	}
-	tsk_user_ns = __task_cred(msg_ctx->task)->user_ns;
-	ctx_euid = task_euid(msg_ctx->task);
-	rc = ecryptfs_find_daemon_by_euid(&daemon, ctx_euid, tsk_user_ns);
-	rcu_read_unlock();
-	mutex_unlock(&ecryptfs_daemon_hash_mux);
-	if (rc) {
-		rc = -EBADMSG;
-		printk(KERN_WARNING "%s: User [%d] received a "
-		       "message response from process [0x%p] but does "
-		       "not have a registered daemon\n", __func__,
-		       ctx_euid, pid);
-		goto wake_up;
-	}
-	if (ctx_euid != euid) {
-		rc = -EBADMSG;
-		printk(KERN_WARNING "%s: Received message from user "
-		       "[%d]; expected message from user [%d]\n", __func__,
-		       euid, ctx_euid);
-		goto unlock;
-	}
-	if (tsk_user_ns != user_ns) {
-		rc = -EBADMSG;
-		printk(KERN_WARNING "%s: Received message from user_ns "
-		       "[0x%p]; expected message from user_ns [0x%p]\n",
-		       __func__, user_ns, tsk_user_ns);
-		goto unlock;
-	}
-	if (daemon->pid != pid) {
-		rc = -EBADMSG;
-		printk(KERN_ERR "%s: User [%d] sent a message response "
-		       "from an unrecognized process [0x%p]\n",
-		       __func__, ctx_euid, pid);
-		goto unlock;
-	}
 	if (msg_ctx->state != ECRYPTFS_MSG_CTX_STATE_PENDING) {
 		rc = -EINVAL;
 		printk(KERN_WARNING "%s: Desired context element is not "
@@ -328,9 +259,8 @@ int ecryptfs_process_response(struct ecryptfs_message *msg, uid_t euid,
 	}
 	memcpy(msg_ctx->msg, msg, msg_size);
 	msg_ctx->state = ECRYPTFS_MSG_CTX_STATE_DONE;
-	rc = 0;
-wake_up:
 	wake_up_process(msg_ctx->task);
+	rc = 0;
 unlock:
 	mutex_unlock(&msg_ctx->mux);
 out:
@@ -352,14 +282,11 @@ ecryptfs_send_message_locked(char *data, int data_len, u8 msg_type,
 			     struct ecryptfs_msg_ctx **msg_ctx)
 {
 	struct ecryptfs_daemon *daemon;
-	uid_t euid = current_euid();
 	int rc;
 
-	rc = ecryptfs_find_daemon_by_euid(&daemon, euid, current_user_ns());
+	rc = ecryptfs_find_daemon_by_euid(&daemon);
 	if (rc || !daemon) {
 		rc = -ENOTCONN;
-		printk(KERN_ERR "%s: User [%d] does not have a daemon "
-		       "registered\n", __func__, euid);
 		goto out;
 	}
 	mutex_lock(&ecryptfs_msg_ctx_lists_mux);