Grant access to a single s3 bucket and nothing else.

s3.json

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "Stmt1475614069000",
      "Effect": "Allow",
      "Action": [
        "s3:*"
      ],
      "Resource": [
        "arn:aws:s3:::bucket/*"
      ]
    },
    {
      "Sid": "Stmt1475614105000",
      "Effect": "Allow",
      "Action": [
        "s3:ListBucket"
      ],
      "Resource": [
        "arn:aws:s3:::bucket"
      ]
    }
  ]
}