Necessary s3cmd S3 permissions for PUT/Sync

Question

In moving to AWS EC2, I want to restrict my instances' user permissions for good reason. One thing the instances need to do is access files on S3 and write files there. However, I cannot find any way to achieve this without giving all permissions to that user.

s3cmd allows me to call "ls" and "du" on the s3 buckets I gave the policy permission to, but always fails with a 403 error when trying to PUT/sync with one of these folders. If I use my root credentials, the transfer goes right through.

So, I don't get why if I give all permissions to the user for said buckets, it cannot PUT, but if I give it arn:aws:s3:::* (all buckets) then it can. Makes no sense to me.

Anyone else ever dealt with this before?

Answer 1

Try something like this. I think the problem is that you need s3:ListAllMyBuckets and s3:ListBuckets for the s3cmd to work. Not sure why but it wont work unless it can get a list of the buckets. I had the same problem the first time i tried to use permissions with s3cmd and this was the solution.

{
  "Statement": [
    {
      "Action": [
        "s3:ListAllMyBuckets"
      ],
      "Effect": "Allow",
      "Resource": "arn:aws:s3:::*"
    },
    {
      "Action": [ 
          "s3:ListBucket", 
          "s3:PutObject",
          "s3:PutObjectAcl"
      ],
      "Effect": "Allow",
      "Resource": [
          "arn:aws:s3:::bucket/path", 
          "arn:aws:s3:::bucket/path/*"
      ]
    }
  ]
}

Edit I've added the s3:PutObjectAcl action which is required for newer versions of s3cmd as stated by Will Jessop below.