Política de IAM e bucket para acesso ao S3

Suporte Instalação
1

Percebi que todos os tutoriais que encontrei sobre acesso ao S3 para o Discourse concediam ao usuário autoridade absoluta sobre o bucket — eles permitem a permissão ‘s3:*’.

Essa é uma política extremamente imprudente, pois concede controle significativamente maior sobre o bucket do que o razoável. Se você estiver usando o S3 para armazenamento de backups do Discourse, um atacante desenfreado seria capaz de excluir seu bucket e seus backups ao sair.

Existem duas maneiras de combater isso: uma, uma política mais restrita…

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "s3:List*",
                "s3:Get*",
                "s3:AbortMultipartUpload",
                "s3:DeleteObject",
                "s3:PutObject"
            ],
            "Resource": [
                "arn:aws:s3:::whatever-bucket",
                "arn:aws:s3:::whatever-bucket/*"
            ]
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": [
                "s3:ListAllMyBuckets",
                "s3:HeadBucket"
            ],
            "Resource": "*"
        }
    ]
}

… e duas, aplicar algumas precauções sensatas à política do bucket. (Isso, na verdade, vai muito além do mínimo necessário, mas eu estava com pressa e não tive tempo para experimentar, e é melhor do que o que encontrei.) Recomendo ativar o versionamento e, em seguida, configurar uma regra de ciclo de vida para “versões anteriores” que as remova após um período razoável, como 21 dias. A política fornecida permitiria a rotação de logs e a exclusão de arquivos, mas não concederia ao usuário com credenciais do S3 acesso para restaurar ou eliminar versões anteriores. Isso significa que, embora eles pudessem excluir um backup, um atacante desenfreado não poderia apagá-lo do histórico de versões antes que um administrador com credenciais de root pudesse recuperá-lo.

Obrigado!

2

This is good advice, certainly, but I’m unsure Discourse should really be considered responsible for giving out advice about S3 best practices?

We could put a note / reminder in the help text for the field, if it can be kept short.

3

Oh, I’m sorry – I wasn’t trying to suggest you /should/ be; certainly I don’t know where you’d put it. I just found that when I Googled “Discourse S3 IAM” all of the example policies were the same awful wide-open one, so I’m reporting what I did instead of that.

(That’s why I seperated this thread from the other.)

4

Were those examples here on meta.discourse.org? If they’re in a howto you might be able to edit them, or you could draft your own and get it moved into #howto:sysadmin.

5

My take on this is that our responsibility for S3 advice is about the same as our advice on things like TLS configs (which we do update on occasion). We should try to stay “safe by default”, because we know that just about everyone’s going to blindly use whatever we suggest, because very few people know what any of this magic actually does. Our as-close-to-official-as-we-get guide on setting up S3 does suggest using the wide-open policy, so I’ll fix that up to be more sensible.

@Asher_Densmore-Lynn: if you find any other examples of problematic IAM policies floating around anywhere we can control (here on meta, git repos under the discourse GitHub user, that sort of thing), feel free to let us (me) know (with a specific reference to what’s problematic; everyone’s Google search results are different), and I’ll get it fixed.

6

Sure, and thanks! I hope you add the part about the bucket versioning – keeping your backups safe from catastrophe is hard to do when you have to allow rotation and deletion. If you need me to go into more detail or explain it better I’ll be happy to oblige.

7

One thing to bear in mind is that the howto I linked above is about asset upload, not backups. The policy required for that is likely to be somewhat different to one required for backups. Also, that howto assumes that Discourse will be creating the bucket, and adding instructions on manually adding versioning and rotation would significantly complicate what is already a bit of a bear of a process. If the versioning/rotation settings can be set at creation time (without opening up the IAM policy to allow an attacker to remove those attributes later), then a PR to Discourse to add that ability (even by default) wouldn’t be a bad idea. Otherwise, I think it’s best if you write a separate “Discourse S3 201: Securitay!” topic, that can be linked from the main howto.

8

I looked at that setup guide – be aware that that bucket creation will fail with those permissions. You’ll want to add s3:CreateBucket if that’s something you want to keep.

9

I already added that action.