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>

1 files changed, 26 insertions, 72 deletions

diff --git a/fs/ecryptfs/miscdev.c b/fs/ecryptfs/miscdev.c
index c0038f6566d..412e6eda25f 100644
--- a/fs/ecryptfs/miscdev.c
+++ b/fs/ecryptfs/miscdev.c
@@ -33,7 +33,7 @@ static atomic_t ecryptfs_num_miscdev_opens;
 
 /**
  * ecryptfs_miscdev_poll
- * @file: dev file (ignored)
+ * @file: dev file
  * @pt: dev poll table (ignored)
  *
  * Returns the poll mask
@@ -41,20 +41,10 @@ static atomic_t ecryptfs_num_miscdev_opens;
 static unsigned int
 ecryptfs_miscdev_poll(struct file *file, poll_table *pt)
 {
-	struct ecryptfs_daemon *daemon;
+	struct ecryptfs_daemon *daemon = file->private_data;
 	unsigned int mask = 0;
-	uid_t euid = current_euid();
-	int rc;
 
-	mutex_lock(&ecryptfs_daemon_hash_mux);
-	/* TODO: Just use file->private_data? */
-	rc = ecryptfs_find_daemon_by_euid(&daemon, euid, current_user_ns());
-	if (rc || !daemon) {
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
-		return -EINVAL;
-	}
 	mutex_lock(&daemon->mux);
-	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		printk(KERN_WARNING "%s: Attempt to poll on zombified "
 		       "daemon\n", __func__);
@@ -79,7 +69,7 @@ out_unlock_daemon:
 /**
  * ecryptfs_miscdev_open
  * @inode: inode of miscdev handle (ignored)
- * @file: file for miscdev handle (ignored)
+ * @file: file for miscdev handle
  *
  * Returns zero on success; non-zero otherwise
  */
@@ -87,7 +77,6 @@ static int
 ecryptfs_miscdev_open(struct inode *inode, struct file *file)
 {
 	struct ecryptfs_daemon *daemon = NULL;
-	uid_t euid = current_euid();
 	int rc;
 
 	mutex_lock(&ecryptfs_daemon_hash_mux);
@@ -98,30 +87,20 @@ ecryptfs_miscdev_open(struct inode *inode, struct file *file)
 		       "count; rc = [%d]\n", __func__, rc);
 		goto out_unlock_daemon_list;
 	}
-	rc = ecryptfs_find_daemon_by_euid(&daemon, euid, current_user_ns());
-	if (rc || !daemon) {
-		rc = ecryptfs_spawn_daemon(&daemon, euid, current_user_ns(),
-					   task_pid(current));
-		if (rc) {
-			printk(KERN_ERR "%s: Error attempting to spawn daemon; "
-			       "rc = [%d]\n", __func__, rc);
-			goto out_module_put_unlock_daemon_list;
-		}
-	}
-	mutex_lock(&daemon->mux);
-	if (daemon->pid != task_pid(current)) {
+	rc = ecryptfs_find_daemon_by_euid(&daemon);
+	if (!rc) {
 		rc = -EINVAL;
-		printk(KERN_ERR "%s: pid [0x%p] has registered with euid [%d], "
-		       "but pid [0x%p] has attempted to open the handle "
-		       "instead\n", __func__, daemon->pid, daemon->euid,
-		       task_pid(current));
-		goto out_unlock_daemon;
+		goto out_unlock_daemon_list;
+	}
+	rc = ecryptfs_spawn_daemon(&daemon, file);
+	if (rc) {
+		printk(KERN_ERR "%s: Error attempting to spawn daemon; "
+		       "rc = [%d]\n", __func__, rc);
+		goto out_module_put_unlock_daemon_list;
 	}
+	mutex_lock(&daemon->mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_MISCDEV_OPEN) {
 		rc = -EBUSY;
-		printk(KERN_ERR "%s: Miscellaneous device handle may only be "
-		       "opened once per daemon; pid [0x%p] already has this "
-		       "handle open\n", __func__, daemon->pid);
 		goto out_unlock_daemon;
 	}
 	daemon->flags |= ECRYPTFS_DAEMON_MISCDEV_OPEN;
@@ -140,7 +119,7 @@ out_unlock_daemon_list:
 /**
  * ecryptfs_miscdev_release
  * @inode: inode of fs/ecryptfs/euid handle (ignored)
- * @file: file for fs/ecryptfs/euid handle (ignored)
+ * @file: file for fs/ecryptfs/euid handle
  *
  * This keeps the daemon registered until the daemon sends another
  * ioctl to fs/ecryptfs/ctl or until the kernel module unregisters.
@@ -150,20 +129,18 @@ out_unlock_daemon_list:
 static int
 ecryptfs_miscdev_release(struct inode *inode, struct file *file)
 {
-	struct ecryptfs_daemon *daemon = NULL;
-	uid_t euid = current_euid();
+	struct ecryptfs_daemon *daemon = file->private_data;
 	int rc;
 
-	mutex_lock(&ecryptfs_daemon_hash_mux);
-	rc = ecryptfs_find_daemon_by_euid(&daemon, euid, current_user_ns());
-	if (rc || !daemon)
-		daemon = file->private_data;
 	mutex_lock(&daemon->mux);
 	BUG_ON(!(daemon->flags & ECRYPTFS_DAEMON_MISCDEV_OPEN));
 	daemon->flags &= ~ECRYPTFS_DAEMON_MISCDEV_OPEN;
 	atomic_dec(&ecryptfs_num_miscdev_opens);
 	mutex_unlock(&daemon->mux);
+
+	mutex_lock(&ecryptfs_daemon_hash_mux);
 	rc = ecryptfs_exorcise_daemon(daemon);
+	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	if (rc) {
 		printk(KERN_CRIT "%s: Fatal error whilst attempting to "
 		       "shut down daemon; rc = [%d]. Please report this "
@@ -171,7 +148,6 @@ ecryptfs_miscdev_release(struct inode *inode, struct file *file)
 		BUG();
 	}
 	module_put(THIS_MODULE);
-	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	return rc;
 }
 
@@ -248,7 +224,7 @@ int ecryptfs_send_miscdev(char *data, size_t data_size,
 
 /**
  * ecryptfs_miscdev_read - format and send message from queue
- * @file: fs/ecryptfs/euid miscdevfs handle (ignored)
+ * @file: miscdevfs handle
  * @buf: User buffer into which to copy the next message on the daemon queue
  * @count: Amount of space available in @buf
  * @ppos: Offset in file (ignored)
@@ -262,43 +238,27 @@ static ssize_t
 ecryptfs_miscdev_read(struct file *file, char __user *buf, size_t count,
 		      loff_t *ppos)
 {
-	struct ecryptfs_daemon *daemon;
+	struct ecryptfs_daemon *daemon = file->private_data;
 	struct ecryptfs_msg_ctx *msg_ctx;
 	size_t packet_length_size;
 	char packet_length[ECRYPTFS_MAX_PKT_LEN_SIZE];
 	size_t i;
 	size_t total_length;
-	uid_t euid = current_euid();
 	int rc;
 
-	mutex_lock(&ecryptfs_daemon_hash_mux);
-	/* TODO: Just use file->private_data? */
-	rc = ecryptfs_find_daemon_by_euid(&daemon, euid, current_user_ns());
-	if (rc || !daemon) {
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
-		return -EINVAL;
-	}
 	mutex_lock(&daemon->mux);
-	if (task_pid(current) != daemon->pid) {
-		mutex_unlock(&daemon->mux);
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
-		return -EPERM;
-	}
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		rc = 0;
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
 		printk(KERN_WARNING "%s: Attempt to read from zombified "
 		       "daemon\n", __func__);
 		goto out_unlock_daemon;
 	}
 	if (daemon->flags & ECRYPTFS_DAEMON_IN_READ) {
 		rc = 0;
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
 		goto out_unlock_daemon;
 	}
 	/* This daemon will not go away so long as this flag is set */
 	daemon->flags |= ECRYPTFS_DAEMON_IN_READ;
-	mutex_unlock(&ecryptfs_daemon_hash_mux);
 check_list:
 	if (list_empty(&daemon->msg_ctx_out_queue)) {
 		mutex_unlock(&daemon->mux);
@@ -382,16 +342,12 @@ out_unlock_daemon:
  * ecryptfs_miscdev_response - miscdevess response to message previously sent to daemon
  * @data: Bytes comprising struct ecryptfs_message
  * @data_size: sizeof(struct ecryptfs_message) + data len
- * @euid: Effective user id of miscdevess sending the miscdev response
- * @user_ns: The namespace in which @euid applies
- * @pid: Miscdevess id of miscdevess sending the miscdev response
  * @seq: Sequence number for miscdev response packet
  *
  * Returns zero on success; non-zero otherwise
  */
-static int ecryptfs_miscdev_response(char *data, size_t data_size,
-				     uid_t euid, struct user_namespace *user_ns,
-				     struct pid *pid, u32 seq)
+static int ecryptfs_miscdev_response(struct ecryptfs_daemon *daemon, char *data,
+				     size_t data_size, u32 seq)
 {
 	struct ecryptfs_message *msg = (struct ecryptfs_message *)data;
 	int rc;
@@ -403,7 +359,7 @@ static int ecryptfs_miscdev_response(char *data, size_t data_size,
 		rc = -EINVAL;
 		goto out;
 	}
-	rc = ecryptfs_process_response(msg, euid, user_ns, pid, seq);
+	rc = ecryptfs_process_response(daemon, msg, seq);
 	if (rc)
 		printk(KERN_ERR
 		       "Error processing response message; rc = [%d]\n", rc);
@@ -413,7 +369,7 @@ out:
 
 /**
  * ecryptfs_miscdev_write - handle write to daemon miscdev handle
- * @file: File for misc dev handle (ignored)
+ * @file: File for misc dev handle
  * @buf: Buffer containing user data
  * @count: Amount of data in @buf
  * @ppos: Pointer to offset in file (ignored)
@@ -428,7 +384,6 @@ ecryptfs_miscdev_write(struct file *file, const char __user *buf,
 	u32 seq;
 	size_t packet_size, packet_size_length;
 	char *data;
-	uid_t euid = current_euid();
 	unsigned char packet_size_peek[ECRYPTFS_MAX_PKT_LEN_SIZE];
 	ssize_t rc;
 
@@ -488,10 +443,9 @@ memdup:
 		}
 		memcpy(&counter_nbo, &data[PKT_CTR_OFFSET], PKT_CTR_SIZE);
 		seq = be32_to_cpu(counter_nbo);
-		rc = ecryptfs_miscdev_response(
+		rc = ecryptfs_miscdev_response(file->private_data,
 				&data[PKT_LEN_OFFSET + packet_size_length],
-				packet_size, euid, current_user_ns(),
-				task_pid(current), seq);
+				packet_size, seq);
 		if (rc) {
 			printk(KERN_WARNING "%s: Failed to deliver miscdev "
 			       "response to requesting operation; rc = [%zd]\n",