ec2上でdocker-compose buildすると permission deniedとなる

ec2上でdocker-composeを実行してサーバーを稼働させようとしているのですが、permission deniedとなってdocker-compose buildができないという状況です。
どうやらmysqlへのアクセス権限に働いているようで、docker/dbなどは同様に削除することすらできません。とりあえず関係ありそうなファイルをのせておきました。
よろしくおねがいします！

docker-compose.yml

version : '3'
services:
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: password
      MYSQL_DATABASE: root
    volumes:
      -./tmp/db:/var/lib/mysql/data
    ports:
      - "3306:3306"

  web:
    tty: true
    stdin_open: true 
    build: .
    command: /bin/sh -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/my_song
    ports:
      - "3000:3000"
    links:
      - db

  server:
    build:
      context: containers/nginx
    volumes:
      - ./nginx/log:/var/log/nginx
      - public-data:/my_song/public
    ports:
      - 80:80 
    depends_on:
      - web
volumes:
  public-data:
  tmp-data:
  log-data:
  db-data:

database.yml

# MySQL. Versions 5.1.10 and up are supported.
#
# Install the MySQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   https://dev.mysql.com/doc/refman/5.7/en/password-hashing.html
#
default: &default
  adapter: mysql2
  encoding: utf8
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  port: 3306
  username: root
  password: password
  host: db

development:
  <<: *default
  database: my_song_development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: my_song_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: myapp_production
  username: myapp
  password: <%= ENV['MYAPP_DATABASE_PASSWORD'] %>