eCryptfs: Add reference counting to lower files

For any given lower inode, eCryptfs keeps only one lower file open and
multiplexes all eCryptfs file operations through that lower file. The
lower file was considered "persistent" and stayed open from the first
lookup through the lifetime of the inode.

This patch keeps the notion of a single, per-inode lower file, but adds
reference counting around the lower file so that it is closed when not
currently in use. If the reference count is at 0 when an operation (such
as open, create, etc.) needs to use the lower file, a new lower file is
opened. Since the file is no longer persistent, all references to the
term persistent file are changed to lower file.

Locking is added around the sections of code that opens the lower file
and assign the pointer in the inode info, as well as the code the fputs
the lower file when all eCryptfs users are done with it.

This patch is needed to fix issues, when mounted on top of the NFSv3
client, where the lower file is left silly renamed until the eCryptfs
inode is destroyed.

Signed-off-by: Tyler Hicks <[e-mail]>

fs/ecryptfs/ecryptfs_kernel.h

···
 struct ecryptfs_inode_info {
 	struct inode vfs_inode;
 	struct inode *wii_inode;
+	struct mutex lower_file_mutex;
+	atomic_t lower_file_count;
 	struct file *lower_file;
 	struct ecryptfs_crypt_stat crypt_stat;
 };
···
 			     struct dentry *lower_dentry,
 			     struct vfsmount *lower_mnt,
 			     const struct cred *cred);
-int ecryptfs_init_persistent_file(struct dentry *ecryptfs_dentry);
+int ecryptfs_get_lower_file(struct dentry *ecryptfs_dentry);
+void ecryptfs_put_lower_file(struct inode *inode);
 int
 ecryptfs_write_tag_70_packet(char *dest, size_t *remaining_bytes,
 			     size_t *packet_size,

fs/ecryptfs/file.c

···
 				      | ECRYPTFS_ENCRYPTED);
 	}
 	mutex_unlock(&crypt_stat->cs_mutex);
-	rc = ecryptfs_init_persistent_file(ecryptfs_dentry);
+	rc = ecryptfs_get_lower_file(ecryptfs_dentry);
 	if (rc) {
 		printk(KERN_ERR "%s: Error attempting to initialize "
-			"the persistent file for the dentry with name "
+			"the lower file for the dentry with name "
 			"[%s]; rc = [%d]\n", __func__,
 			ecryptfs_dentry->d_name.name, rc);
 		goto out_free;
···
 	if ((ecryptfs_inode_to_private(inode)->lower_file->f_flags & O_ACCMODE)
 	    == O_RDONLY && (file->f_flags & O_ACCMODE) != O_RDONLY) {
 		rc = -EPERM;
-		printk(KERN_WARNING "%s: Lower persistent file is RO; eCryptfs "
+		printk(KERN_WARNING "%s: Lower file is RO; eCryptfs "
 		       "file must hence be opened RO\n", __func__);
-		goto out_free;
+		goto out_put;
 	}
 	ecryptfs_set_file_lower(
 		file, ecryptfs_inode_to_private(inode)->lower_file);
···
 				       "Plaintext passthrough mode is not "
 				       "enabled; returning -EIO\n");
 				mutex_unlock(&crypt_stat->cs_mutex);
-				goto out_free;
+				goto out_put;
 			}
 			rc = 0;
 			crypt_stat->flags &= ~(ECRYPTFS_ENCRYPTED);
···
 			"[0x%.16lx] size: [0x%.16llx]\n", inode, inode->i_ino,
 			(unsigned long long)i_size_read(inode));
 	goto out;
+out_put:
+	ecryptfs_put_lower_file(inode);
 out_free:
 	kmem_cache_free(ecryptfs_file_info_cache,
 			ecryptfs_file_to_private(file));
···
 
 static int ecryptfs_flush(struct file *file, fl_owner_t td)
 {
-	int rc = 0;
-	struct file *lower_file = NULL;
-
-	lower_file = ecryptfs_file_to_lower(file);
-	if (lower_file->f_op && lower_file->f_op->flush)
-		rc = lower_file->f_op->flush(lower_file, td);
-	return rc;
+	return file->f_mode & FMODE_WRITE
+	       ? filemap_write_and_wait(file->f_mapping) : 0;
 }
 
 static int ecryptfs_release(struct inode *inode, struct file *file)
 {
+	ecryptfs_put_lower_file(inode);
 	kmem_cache_free(ecryptfs_file_info_cache,
 			ecryptfs_file_to_private(file));
 	return 0;

fs/ecryptfs/inode.c

···
 				"context; rc = [%d]\n", rc);
 		goto out;
 	}
-	rc = ecryptfs_init_persistent_file(ecryptfs_dentry);
+	rc = ecryptfs_get_lower_file(ecryptfs_dentry);
 	if (rc) {
 		printk(KERN_ERR "%s: Error attempting to initialize "
-			"the persistent file for the dentry with name "
+			"the lower file for the dentry with name "
 			"[%s]; rc = [%d]\n", __func__,
 			ecryptfs_dentry->d_name.name, rc);
 		goto out;
 	}
 	rc = ecryptfs_write_metadata(ecryptfs_dentry);
-	if (rc) {
+	if (rc)
 		printk(KERN_ERR "Error writing headers; rc = [%d]\n", rc);
-		goto out;
-	}
+	ecryptfs_put_lower_file(ecryptfs_dentry->d_inode);
 out:
 	return rc;
 }
···
 	struct ecryptfs_crypt_stat *crypt_stat;
 	char *page_virt = NULL;
 	u64 file_size;
-	int rc = 0;
+	int put_lower = 0, rc = 0;
 
 	lower_dir_dentry = lower_dentry->d_parent;
 	lower_mnt = mntget(ecryptfs_dentry_to_lower_mnt(
···
 		rc = -ENOMEM;
 		goto out;
 	}
-	rc = ecryptfs_init_persistent_file(ecryptfs_dentry);
+	rc = ecryptfs_get_lower_file(ecryptfs_dentry);
 	if (rc) {
 		printk(KERN_ERR "%s: Error attempting to initialize "
-			"the persistent file for the dentry with name "
+			"the lower file for the dentry with name "
 			"[%s]; rc = [%d]\n", __func__,
 			ecryptfs_dentry->d_name.name, rc);
 		goto out_free_kmem;
 	}
+	put_lower = 1;
 	crypt_stat = &ecryptfs_inode_to_private(
 					ecryptfs_dentry->d_inode)->crypt_stat;
 	/* TODO: lock for crypt_stat comparison */
···
 	mntput(lower_mnt);
 	d_drop(ecryptfs_dentry);
 out:
+	if (put_lower)
+		ecryptfs_put_lower_file(ecryptfs_dentry->d_inode);
 	return rc;
 }
 
···
 
 	if (unlikely((ia->ia_size == i_size))) {
 		lower_ia->ia_valid &= ~ATTR_SIZE;
-		goto out;
+		return 0;
 	}
+	rc = ecryptfs_get_lower_file(dentry);
+	if (rc)
+		return rc;
 	crypt_stat = &ecryptfs_inode_to_private(dentry->d_inode)->crypt_stat;
 	/* Switch on growing or shrinking file */
 	if (ia->ia_size > i_size) {
···
 			lower_ia->ia_valid &= ~ATTR_SIZE;
 	}
 out:
+	ecryptfs_put_lower_file(inode);
 	return rc;
 }
 
···
 
 		mount_crypt_stat = &ecryptfs_superblock_to_private(
 			dentry->d_sb)->mount_crypt_stat;
+		rc = ecryptfs_get_lower_file(dentry);
+		if (rc) {
+			mutex_unlock(&crypt_stat->cs_mutex);
+			goto out;
+		}
 		rc = ecryptfs_read_metadata(dentry);
+		ecryptfs_put_lower_file(inode);
 		if (rc) {
 			if (!(mount_crypt_stat->flags
 			      & ECRYPTFS_PLAINTEXT_PASSTHROUGH_ENABLED)) {

fs/ecryptfs/kthread.c

···
  * @ignored: ignored
  *
  * The eCryptfs kernel thread that has the responsibility of getting
- * the lower persistent file with RW permissions.
+ * the lower file with RW permissions.
  *
  * Returns zero on success; non-zero otherwise
  */
···
 	int rc = 0;
 
 	/* Corresponding dput() and mntput() are done when the
-	 * persistent file is fput() when the eCryptfs inode is
-	 * destroyed. */
+	 * lower file is fput() when all eCryptfs files for the inode are
+	 * released. */
 	dget(lower_dentry);
 	mntget(lower_mnt);
 	flags |= IS_RDONLY(lower_dentry->d_inode) ? O_RDONLY : O_RDWR;

fs/ecryptfs/main.c

···
 }
 
 /**
- * ecryptfs_init_persistent_file
+ * ecryptfs_init_lower_file
  * @ecryptfs_dentry: Fully initialized eCryptfs dentry object, with
  *                   the lower dentry and the lower mount set
  *
···
  * inode. All I/O operations to the lower inode occur through that
  * file. When the first eCryptfs dentry that interposes with the first
  * lower dentry for that inode is created, this function creates the
- * persistent file struct and associates it with the eCryptfs
- * inode. When the eCryptfs inode is destroyed, the file is closed.
+ * lower file struct and associates it with the eCryptfs
+ * inode. When all eCryptfs files associated with the inode are released, the
+ * file is closed.
  *
- * The persistent file will be opened with read/write permissions, if
+ * The lower file will be opened with read/write permissions, if
  * possible. Otherwise, it is opened read-only.
  *
- * This function does nothing if a lower persistent file is already
+ * This function does nothing if a lower file is already
  * associated with the eCryptfs inode.
  *
  * Returns zero on success; non-zero otherwise
  */
-int ecryptfs_init_persistent_file(struct dentry *ecryptfs_dentry)
+static int ecryptfs_init_lower_file(struct dentry *dentry,
+				    struct file **lower_file)
 {
 	const struct cred *cred = current_cred();
-	struct ecryptfs_inode_info *inode_info =
-		ecryptfs_inode_to_private(ecryptfs_dentry->d_inode);
-	int rc = 0;
+	struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
+	struct vfsmount *lower_mnt = ecryptfs_dentry_to_lower_mnt(dentry);
+	int rc;
 
-	if (!inode_info->lower_file) {
-		struct dentry *lower_dentry;
-		struct vfsmount *lower_mnt =
-			ecryptfs_dentry_to_lower_mnt(ecryptfs_dentry);
-
-		lower_dentry = ecryptfs_dentry_to_lower(ecryptfs_dentry);
-		rc = ecryptfs_privileged_open(&inode_info->lower_file,
-					      lower_dentry, lower_mnt, cred);
-		if (rc) {
-			printk(KERN_ERR "Error opening lower persistent file "
-			       "for lower_dentry [0x%p] and lower_mnt [0x%p]; "
-			       "rc = [%d]\n", lower_dentry, lower_mnt, rc);
-			inode_info->lower_file = NULL;
-		}
+	rc = ecryptfs_privileged_open(lower_file, lower_dentry, lower_mnt,
+				      cred);
+	if (rc) {
+		printk(KERN_ERR "Error opening lower file "
+		       "for lower_dentry [0x%p] and lower_mnt [0x%p]; "
+		       "rc = [%d]\n", lower_dentry, lower_mnt, rc);
+		(*lower_file) = NULL;
 	}
 	return rc;
+}
+
+int ecryptfs_get_lower_file(struct dentry *dentry)
+{
+	struct ecryptfs_inode_info *inode_info =
+		ecryptfs_inode_to_private(dentry->d_inode);
+	int count, rc = 0;
+
+	mutex_lock(&inode_info->lower_file_mutex);
+	count = atomic_inc_return(&inode_info->lower_file_count);
+	if (WARN_ON_ONCE(count < 1))
+		rc = -EINVAL;
+	else if (count == 1) {
+		rc = ecryptfs_init_lower_file(dentry,
+					      &inode_info->lower_file);
+		if (rc)
+			atomic_set(&inode_info->lower_file_count, 0);
+	}
+	mutex_unlock(&inode_info->lower_file_mutex);
+	return rc;
+}
+
+void ecryptfs_put_lower_file(struct inode *inode)
+{
+	struct ecryptfs_inode_info *inode_info;
+
+	inode_info = ecryptfs_inode_to_private(inode);
+	if (atomic_dec_and_mutex_lock(&inode_info->lower_file_count,
+				      &inode_info->lower_file_mutex)) {
+		fput(inode_info->lower_file);
+		inode_info->lower_file = NULL;
+		mutex_unlock(&inode_info->lower_file_mutex);
+	}
 }
 
 static struct inode *ecryptfs_get_inode(struct inode *lower_inode,

fs/ecryptfs/super.c

···
 	if (unlikely(!inode_info))
 		goto out;
 	ecryptfs_init_crypt_stat(&inode_info->crypt_stat);
+	mutex_init(&inode_info->lower_file_mutex);
+	atomic_set(&inode_info->lower_file_count, 0);
 	inode_info->lower_file = NULL;
 	inode = &inode_info->vfs_inode;
 out:
···
  *
  * This is used during the final destruction of the inode.  All
  * allocation of memory related to the inode, including allocated
- * memory in the crypt_stat struct, will be released here. This
- * function also fput()'s the persistent file for the lower inode.
+ * memory in the crypt_stat struct, will be released here.
  * There should be no chance that this deallocation will be missed.
  */
 static void ecryptfs_destroy_inode(struct inode *inode)
···
 	struct ecryptfs_inode_info *inode_info;
 
 	inode_info = ecryptfs_inode_to_private(inode);
-	if (inode_info->lower_file) {
-		struct dentry *lower_dentry =
-			inode_info->lower_file->f_dentry;
-
-		BUG_ON(!lower_dentry);
-		if (lower_dentry->d_inode) {
-			fput(inode_info->lower_file);
-			inode_info->lower_file = NULL;
-		}
-	}
+	BUG_ON(inode_info->lower_file);
 	ecryptfs_destroy_crypt_stat(&inode_info->crypt_stat);
 	call_rcu(&inode->i_rcu, ecryptfs_i_callback);
 }