eCryptfs: Return error when lower file pointer is NULL

When an eCryptfs inode's lower file has been closed, and the pointer has
been set to NULL, return an error when trying to do a lower read or
write rather than calling BUG().

https://bugzilla.kernel.org/show_bug.cgi?id=37292

Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Cc: <stable@kernel.org>

fs/ecryptfs/read_write.c

@@ -39,15 +39,16 @@
 int ecryptfs_write_lower(struct inode *ecryptfs_inode, char *data,
 			 loff_t offset, size_t size)
 {
-	struct ecryptfs_inode_info *inode_info;
+	struct file *lower_file;
 	mm_segment_t fs_save;
 	ssize_t rc;
 
-	inode_info = ecryptfs_inode_to_private(ecryptfs_inode);
-	BUG_ON(!inode_info->lower_file);
+	lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
+	if (!lower_file)
+		return -EIO;
 	fs_save = get_fs();
 	set_fs(get_ds());
-	rc = vfs_write(inode_info->lower_file, data, size, &offset);
+	rc = vfs_write(lower_file, data, size, &offset);
 	set_fs(fs_save);
 	mark_inode_dirty_sync(ecryptfs_inode);
 	return rc;
@@ -225,15 +226,16 @@ out:
 int ecryptfs_read_lower(char *data, loff_t offset, size_t size,
 			struct inode *ecryptfs_inode)
 {
-	struct ecryptfs_inode_info *inode_info =
-		ecryptfs_inode_to_private(ecryptfs_inode);
+	struct file *lower_file;
 	mm_segment_t fs_save;
 	ssize_t rc;
 
-	BUG_ON(!inode_info->lower_file);
+	lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
+	if (!lower_file)
+		return -EIO;
 	fs_save = get_fs();
 	set_fs(get_ds());
-	rc = vfs_read(inode_info->lower_file, data, size, &offset);
+	rc = vfs_read(lower_file, data, size, &offset);
 	set_fs(fs_save);
 	return rc;
 }