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gs: allow backend creation without storage.buckets.get

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If the service account used with restic does not have the
storage.buckets.get permission (in the "Storage Admin" role), Create
cannot use Get to determine if the bucket is accessible.

Rather than always trying to create the bucket on Get error, gracefully
fall back to assuming the bucket is accessible. If it is, restic init
will complete successfully. If it is not, it will fail on a later call.

Here is what init looks like now in different cases.

Service account without "Storage Admin":

Bucket exists and is accessible (this is the case that didn't work
before):

$ ./restic init -r gs:this-bucket-does-exist:/
enter password for new backend:
enter password again:
created restic backend c02e2edb67 at gs:this-bucket-does-exist:/

Please note that knowledge of your password is required to access
the repository. Losing your password means that your data is
irrecoverably lost.

Bucket exists but is not accessible:

$ ./restic init -r gs:this-bucket-does-exist:/
enter password for new backend:
enter password again:
create key in backend at gs:this-bucket-does-exist:/ failed:
service.Objects.Insert: googleapi: Error 403:
my-service-account@myproject.iam.gserviceaccount.com does not have
storage.objects.create access to object this-bucket-exists/keys/0fa714e695c8ecd58cb467cdeb04d36f3b710f883496a90f23cae0315daf0b93., forbidden

Bucket does not exist:

$ ./restic init -r gs:this-bucket-does-not-exist:/
create backend at gs:this-bucket-does-not-exist:/ failed:
service.Buckets.Insert: googleapi: Error 403:
my-service-account@myproject.iam.gserviceaccount.com does not have storage.buckets.create access to bucket this-bucket-does-not-exist., forbidden

Service account with "Storage Admin":

Bucket exists and is accessible: Same

Bucket exists but is not accessible: Same. Previously this would fail
when Create tried to create the bucket. Now it fails when trying to
create the keys.

Bucket does not exist:

$ ./restic init -r gs:this-bucket-does-not-exist:/
enter password for new backend:
enter password again:
created restic backend c3c48b481d at gs:this-bucket-does-not-exist:/

Please note that knowledge of your password is required to access
the repository. Losing your password means that your data is
irrecoverably lost.
This commit is contained in:
Michael Pratt
2017-09-25 21:53:21 -07:00
parent 7e8bc8d362
commit fa0be82da8
3 changed files with 59 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

53
internal/backend/gs/gs.go
View File

@@ -99,27 +99,58 @@ func Open(cfg Config) (restic.Backend, error) {
return open(cfg)
}
// Create opens the gs backend at the specified bucket and creates the bucket
// if it does not exist yet.
// Create opens the gs backend at the specified bucket and attempts to creates
// the bucket if it does not exist yet.
//
// In addition to the permissions required by Backend, Create requires these
// permissions:
// * storage.buckets.get
// * storage.buckets.create (if the bucket doesn't exist)
// The service account must have the "storage.buckets.create" permission to
// create a bucket the does not yet exist.
func Create(cfg Config) (restic.Backend, error) {
be, err := open(cfg)
if err != nil {
return nil, errors.Wrap(err, "open")
}
// Create bucket if it doesn't exist.
// Try to determine if the bucket exists. If it does not, try to create it.
//
// A Get call has three typical error cases:
//
// * nil: Bucket exists and we have access to the metadata (returned).
//
// * 403: Bucket exists and we do not have access to the metadata. We
// don't have storage.buckets.get permission to the bucket, but we may
// still be able to access objects in the bucket.
//
// * 404: Bucket doesn't exist.
//
// Determining if the bucket is accessible is best-effort because the
// 403 case is ambiguous.
if _, err := be.service.Buckets.Get(be.bucketName).Do(); err != nil {
bucket := &storage.Bucket{
Name: be.bucketName,
gerr, ok := err.(*googleapi.Error)
if !ok {
// Don't know what to do with this error.
return nil, errors.Wrap(err, "service.Buckets.Get")
}
if _, err := be.service.Buckets.Insert(be.projectID, bucket).Do(); err != nil {
return nil, errors.Wrap(err, "service.Buckets.Insert")
switch gerr.Code {
case 403:
// Bucket exists, but we don't know if it is
// accessible. Optimistically assume it is; if not,
// future Backend calls will fail.
debug.Log("Unable to determine if bucket %s is accessible (err %v). Continuing as if it is.", be.bucketName, err)
case 404:
// Bucket doesn't exist, try to create it.
bucket := &storage.Bucket{
Name: be.bucketName,
}
if _, err := be.service.Buckets.Insert(be.projectID, bucket).Do(); err != nil {
// Always an error, as the bucket definitely
// doesn't exist.
return nil, errors.Wrap(err, "service.Buckets.Insert")
}
default:
// Don't know what to do with this error.
return nil, errors.Wrap(err, "service.Buckets.Get")
}
}