Necessary s3cmd S3 permissions for PUT/Sync - amazon-s3

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.

Answer 2

bwight's answer is almost right (it probably used to be for older versions of s3cmd), but I need to add a s3:PutObjectAcl to get it to work:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "Stmt123456",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets"
],
"Resource": [
"arn:aws:s3:::*"
]
},
{
"Sid": "Stmt123457",
"Effect": "Allow",
"Action": [
"s3:ListBucket",
"s3:PutObject",
"s3:PutObjectAcl"
],
"Resource": [
"arn:aws:s3:::bucketname",
"arn:aws:s3:::bucketname/*"
]
}
]
}

Answer 3

I was trying to do big file uploads and the policy wasn't working well for me, I ended adding the next policy to the user:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "Stmt1397834652000",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets"
],
"Resource": [
"arn:aws:s3:::*"
]
},
{
"Sid": "Stmt1397834745000",
"Effect": "Allow",
"Action": [
"s3:ListBucket",
"s3:ListBucketMultipartUploads",
"s3:GetBucketLocation",
"s3:AbortMultipartUpload",
"s3:GetObjectAcl",
"s3:GetObjectVersion",
"s3:DeleteObject",
"s3:DeleteObjectVersion",
"s3:GetObject",
"s3:PutObjectAcl",
"s3:PutObject",
"s3:GetObjectVersionAcl"
],
"Resource": [
"arn:aws:s3:::my_bucket",
"arn:aws:s3:::my_bucket/*"
]
}
]
}
where my_bucket is the bucket where I need to manage files though s3cmd

Answer 4

In case you are giving access to a subfolder (as in the original answer of /bucket-name/path/) and not the entire bucket, the ListBucket action requires a bit more specificity:
{
"Sid": "AllowListingOfFilesInFolder",
"Effect": "Allow",
"Action": [
"s3:ListBucket"
],
"Resource": [
"arn:aws:s3:::bucket-name"
],
"Condition": {
"StringLike": {
"s3:prefix": [
"path/*"
]
}
}
}
I believe it works also with the original answer in case you provide access to the entire bucket.