Virus Scanning of Files

This is the Design document for PLFM-4930

Since Synapse hosts files uploaded by users, we must scan user uploaded content to mitigate spread of malware. ClamAV is the recommended open-source antivirus solution.

We are using a fork of an existing Github Project created by Upside Travel.

How it works

A brief overview of the system is listed below (diagram created using https://cloudcraft.co/):

Once a file is tagged as INFECTED, a S3 bucket policy prevents the file from being downloaded. Users attempting to download it will get an HTTP 403 Access Denied from Amazon S3.

There is currently nothing checking the Dead Letter SQS. Its purpose is to catch SNS messages that were unable to be delivered to the Scanner Lambda so that undelivered messages do not fail silently.

Building/installing the scanner

1. git clone https://github.com/Sage-Bionetworks/bucket-antivirus-function
   On Windows make sure you have cloned it with Unix-style line endings (LF) instead of Windows-style line endings (CRLF). You may do this by changing your git config or just run the dos2unix utility on the folder.
2. Download Docker Community Edition: https://www.docker.com/community-edition#/download

3. On Mac/Linux enter the following commands your cloned bucket-antivirus-function folder

   make

   On Windows using Command Prompt while inside the bucket-antivirus-function folder(In File Explorer hold down Shift key and right-click then select "Open command window here"). This is just the same command that is run by make but pwd does not work on Windows and must be substituted with %CD%.

   docker run --rm -ti -v %CD%:/opt/app amazonlinux:latest /bin/bash -c "cd /opt/app && ./build_lambda.sh"

   If you did not check out the git repository with Unix-style line endings on Windows you may get an error: ": No such file or directory"

4. The build should have created a file called /build/lambda.zip
5. Upload the zip file to an S3 Bucket that you own. This is how the CloudFormation stack will access your built lambda.zip
6. Create a CloudFormation Stack with using virus-scan-cloudformation.json located in the git repository.

Triggering the scanner manually:

Normally, files will be automatically scanned upload. However, it may be beneficial to rescan files when new virus definitions are added. To trigger the Scanner Lambda manually, a JSON message that mimics the S3 Event Notification JSON format must be written to the Scanner Trigger SNS. Below is a stripped down JSON example that contains all the information that the scanner will need from the JSON:

{
  "Records": [
    {
      "eventSource": "aws:s3",
      "eventName": "ObjectCreated:Put",
      "s3": {
        "bucket": {
          "name": "test.scan.bucket.sagebase.org"
        },
        "object": {
          "key": "eicar.com",
        }
      }
    }
  ]
}

Limitations

• We can only scan files up to a certain size (25MB). It is very time/resource consuming to scan very large files (if we scan every file uploaded) and most files containing virus are small in size.