attest-provider/pkg/handler/validate.go

/*
   Copyright Docker attest-provider authors

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package handler

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"runtime/debug"

	"github.com/docker/attest"
	"github.com/docker/attest-provider/pkg/utils"
	"github.com/docker/attest/mapping"
	"github.com/docker/attest/oci"
	"github.com/docker/attest/policy"
	"github.com/docker/attest/tuf"
	intoto "github.com/in-toto/in-toto-golang/in_toto"
	"github.com/open-policy-agent/frameworks/constraint/pkg/externaldata"
	"k8s.io/klog/v2"
)

type ValidationResult struct {
	Outcome    attest.Outcome     `json:"outcome"`
	Input      *policy.Input      `json:"input"`
	VSA        *intoto.Statement  `json:"vsa"`
	Violations []policy.Violation `json:"violations"`
}

type ValidateHandlerOptions struct {
	TUFRoot        string
	TUFChannel     string
	TUFOutputPath  string
	TUFMetadataURL string
	TUFTargetsURL  string

	PolicyDir      string
	PolicyCacheDir string

	AttestationStyle string
	ReferrersRepo    string
	Parameters       map[string]string
}

type validateHandler struct {
	opts *ValidateHandlerOptions
}

func NewValidateHandler(ctx context.Context, opts *ValidateHandlerOptions) (http.Handler, error) {
	handler := &validateHandler{opts: opts}

	// a TUF client can only be used once, so we need to create a new one for each request.
	// we create this one up front to ensure that the TUF root is valid and to pre-load the metadata.
	// TODO: this pre-loading works for the root, targets, snapshot, and timestamp roles, but not for delegated roles.
	_, err := handler.newVerifier(ctx)
	if err != nil {
		// if this failed, don't return an error, just log it and continue
		// this prevents the server from getting into a crash loop if the TUF repo is down or broken,
		// and we can still recover if the TUF repo comes back up.
		klog.ErrorS(err, "failed to initialize TUF client")
	}

	klog.Infof("validate handler initialized with %s TUF root", opts.TUFRoot)

	return handler, nil
}

func (h *validateHandler) newVerifier(ctx context.Context) (*attest.ImageVerifier, error) {
	root, err := tuf.GetEmbeddedRoot(h.opts.TUFRoot)
	if err != nil {
		return nil, err
	}

	policyOpts := &policy.Options{
		TUFClientOptions: &tuf.ClientOptions{
			InitialRoot:     root.Data,
			LocalStorageDir: h.opts.TUFOutputPath,
			MetadataSource:  h.opts.TUFMetadataURL,
			TargetsSource:   h.opts.TUFTargetsURL,
			PathPrefix:      h.opts.TUFChannel,
			VersionChecker:  tuf.NewDefaultVersionChecker(),
		},
		LocalTargetsDir:  h.opts.PolicyCacheDir,
		LocalPolicyDir:   h.opts.PolicyDir,
		AttestationStyle: mapping.AttestationStyle(h.opts.AttestationStyle),
		ReferrersRepo:    h.opts.ReferrersRepo,
		Debug:            true,
		Parameters:       h.opts.Parameters,
	}
	verifier, err := attest.NewImageVerifier(ctx, policyOpts)
	if err != nil {
		return nil, err
	}
	return verifier, nil
}

func (h *validateHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	defer func() {
		if r := recover(); r != nil {
			klog.Error(string(debug.Stack()))
			klog.ErrorS(fmt.Errorf("%v", r), "panic occurred")
		}
	}()

	ctx := req.Context()

	// read request body
	requestBody, err := io.ReadAll(req.Body)
	if err != nil {
		utils.SendResponse(nil, fmt.Sprintf("unable to read request body: %v", err), w)
		return
	}

	klog.InfoS("received request", "body", requestBody)

	// parse request body
	var providerRequest externaldata.ProviderRequest
	err = json.Unmarshal(requestBody, &providerRequest)
	if err != nil {
		utils.SendResponse(nil, fmt.Sprintf("unable to unmarshal request body: %v", err), w)
		return
	}

	// create a new verifier for each request
	attest, err := h.newVerifier(ctx)
	if err != nil {
		utils.SendResponse(nil, fmt.Sprintf("unable to create verifier: %v", err), w)
		return
	}

	results := make([]externaldata.Item, 0)
	for _, key := range providerRequest.Request.Keys {
		platform := "linux/amd64"
		src, err := oci.ParseImageSpec(key, oci.WithPlatform(platform))
		if err != nil {
			utils.SendResponse(nil, err.Error(), w)
			return
		}

		result, err := attest.Verify(ctx, src)
		if err != nil {
			utils.SendResponse(nil, err.Error(), w)
			return
		}

		results = append(results, externaldata.Item{
			Key: key,
			Value: ValidationResult{
				Outcome:    result.Outcome,
				Input:      result.Input,
				VSA:        result.VSA,
				Violations: result.Violations,
			},
		})
	}
	utils.SendResponse(&results, "", w)
}