internal/worker/update.go - vulndb - Git at Google

 // Copyright 2021 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package worker

 import (
 	"context"
 	"errors"
 	"fmt"
 	"path"
 	"strings"
 	"time"

 	"github.com/go-git/go-git/v5"
 	"github.com/go-git/go-git/v5/plumbing/object"
 	"golang.org/x/exp/event"
 	"golang.org/x/vulndb/internal/cvelistrepo"
 	"golang.org/x/vulndb/internal/cveschema"
 	"golang.org/x/vulndb/internal/derrors"
 	"golang.org/x/vulndb/internal/worker/log"
 	"golang.org/x/vulndb/internal/worker/store"
 )

 // A triageFunc triages a CVE: it decides whether an issue needs to be filed.
 // If so, it returns a non-empty string indicating the possibly
 // affected module.
 type triageFunc func(*cveschema.CVE) (*triageResult, error)

 // A cveUpdater performs an update operation on the DB.
 type cveUpdater struct {
 	repo           *git.Repository
 	commit         *object.Commit
 	st             store.Store
 	knownIDs       map[string]bool
 	affectedModule triageFunc
 }

 type updateStats struct {
 	skipped                             bool // directory skipped because hashes match
 	numProcessed, numAdded, numModified int
 }

 // newCVEUpdater creates an updater for updating the store with information from
 // the repo commit.
 // needsIssue determines whether a CVE needs an issue to be filed for it.
 func newCVEUpdater(repo *git.Repository, commit *object.Commit, st store.Store, knownVulnIDs []string, needsIssue triageFunc) *cveUpdater {
 	u := &cveUpdater{
 		repo:           repo,
 		commit:         commit,
 		st:             st,
 		knownIDs:       map[string]bool{},
 		affectedModule: needsIssue,
 	}
 	for _, k := range knownVulnIDs {
 		u.knownIDs[k] = true
 	}
 	return u
 }

 // update updates the DB to match the repo at the given commit.
 // It also triages new or changed issues.
 func (u *cveUpdater) update(ctx context.Context) (ur *store.CommitUpdateRecord, err error) {
 	// We want the action of reading the old DB record, updating it and
 	// writing it back to be atomic. It would be too expensive to do that one
 	// record at a time. Ideally we'd process the whole repo commit in one
 	// transaction, but Firestore has a limit on how many writes one
 	// transaction can do, so the CVE files in the repo are processed in
 	// batches, one transaction per batch.
 	defer derrors.Wrap(&err, "cveUpdater.update(%s)", u.commit.Hash)
 	ctx = event.Start(ctx, "cveUpdater.update")
 	defer event.End(ctx)

 	defer func() {
 		if err != nil {
 			log.Errorf(ctx, "update failed: %v", err)
 		} else {
 			var nAdded, nModified int64
 			if ur != nil {
 				nAdded = int64(ur.NumAdded)
 				nModified = int64(ur.NumModified)
 			}
 			log.Infof(ctx, "update succeeded on %s: added %d, modified %d",
 				u.commit.Hash, nAdded, nModified)
 		}
 	}()

 	log.Infof(ctx, "CVE update starting on %s", u.commit.Hash)

 	// Get all the CVE files.
 	// It is cheaper to read all the files from the repo and compare
 	// them to the DB in bulk, than to walk the repo and process
 	// each file individually.
 	files, err := cvelistrepo.Files(u.repo, u.commit)
 	if err != nil {
 		return nil, err
 	}
 	// Process files in the same directory together, so we can easily skip
 	// the entire directory if it hasn't changed.
 	filesByDir, err := groupFilesByDirectory(files)
 	if err != nil {
 		return nil, err
 	}

 	// Create a new CommitUpdateRecord to describe this run of doUpdate.
 	ur = &store.CommitUpdateRecord{
 		StartedAt:  time.Now(),
 		CommitHash: u.commit.Hash.String(),
 		CommitTime: u.commit.Committer.When,
 		NumTotal:   len(files),
 	}
 	if err := u.st.CreateCommitUpdateRecord(ctx, ur); err != nil {
 		return ur, err
 	}

 	var skippedDirs []string
 	const logSkippedEvery = 20 // Log a message every this many skipped directories.
 	for _, dirFiles := range filesByDir {
 		stats, err := u.updateDirectory(ctx, dirFiles)
 		// Change the CommitUpdateRecord in the Store to reflect the results of the directory update.
 		if err != nil {
 			ur.Error = err.Error()
 			if err2 := u.st.SetCommitUpdateRecord(ctx, ur); err2 != nil {
 				return ur, fmt.Errorf("update failed with %w, could not set update record: %v", err, err2)
 			}
 		}
 		if stats.skipped {
 			skippedDirs = append(skippedDirs, dirFiles[0].DirPath)
 			if len(skippedDirs) >= logSkippedEvery {
 				log.Infof(ctx, "skipping directory %s and %d others because the hashes match",
 					skippedDirs[0], len(skippedDirs)-1)
 				skippedDirs = nil
 			}
 		}
 		ur.NumProcessed += stats.numProcessed
 		ur.NumAdded += stats.numAdded
 		ur.NumModified += stats.numModified
 		if err := u.st.SetCommitUpdateRecord(ctx, ur); err != nil {
 			return ur, err
 		}
 	}
 	ur.EndedAt = time.Now()
 	return ur, u.st.SetCommitUpdateRecord(ctx, ur)
 }

 // Firestore supports a maximum of 500 writes per transaction.
 // See https://cloud.google.com/firestore/quotas.
 const maxTransactionWrites = 500

 func (u *cveUpdater) updateDirectory(ctx context.Context, dirFiles []cvelistrepo.File) (_ updateStats, err error) {
 	dirPath := dirFiles[0].DirPath
 	dirHash := dirFiles[0].TreeHash.String()

 	// A non-empty directory hash means that we have fully processed the directory
 	// with that hash. If the stored hash matches the current one, we can skip
 	// this directory.
 	dbHash, err := u.st.GetDirectoryHash(ctx, dirPath)
 	if err != nil {
 		return updateStats{}, err
 	}
 	if dirHash == dbHash {
 		return updateStats{skipped: true}, nil
 	}
 	// Set the hash to something that can't match, until we fully process this directory.
 	if err := u.st.SetDirectoryHash(ctx, dirPath, "in progress"); err != nil {
 		return updateStats{}, err
 	}
 	// It's okay if we crash now; the directory hashes are just an optimization.
 	// At worst we'll redo this directory next time.

 	// Update files in batches.

 	var stats updateStats
 	for i := 0; i < len(dirFiles); i += maxTransactionWrites {
 		j := i + maxTransactionWrites
 		if j > len(dirFiles) {
 			j = len(dirFiles)
 		}
 		numBatchAdds, numBatchMods, err := u.updateBatch(ctx, dirFiles[i:j])
 		if err != nil {
 			return updateStats{}, err
 		}
 		stats.numProcessed += j - i
 		// Add in these two numbers here, instead of in the function passed to
 		// RunTransaction, because that function may be executed multiple times.
 		stats.numAdded += numBatchAdds
 		stats.numModified += numBatchMods
 	} // end batch loop

 	// We're done with this directory, so we can remember its hash.
 	if err := u.st.SetDirectoryHash(ctx, dirPath, dirHash); err != nil {
 		return updateStats{}, err
 	}
 	return stats, nil
 }

 func (u *cveUpdater) updateBatch(ctx context.Context, batch []cvelistrepo.File) (numAdds, numMods int, err error) {
 	startID := idFromFilename(batch[0].Filename)
 	endID := idFromFilename(batch[len(batch)-1].Filename)
 	defer derrors.Wrap(&err, "updateBatch(%s-%s)", startID, endID)

 	err = u.st.RunTransaction(ctx, func(ctx context.Context, tx store.Transaction) error {
 		numAdds = 0
 		numMods = 0

 		// Read information about the existing state in the store that's
 		// relevant to this batch. Since the entries are sorted, we can read
 		// a range of IDS.
 		crs, err := tx.GetCVERecords(startID, endID)
 		if err != nil {
 			return err
 		}
 		idToRecord := map[string]*store.CVERecord{}
 		for _, cr := range crs {
 			idToRecord[cr.ID] = cr
 		}
 		// Determine what needs to be added and modified.
 		for _, f := range batch {
 			id := idFromFilename(f.Filename)
 			old := idToRecord[id]
 			if old != nil && old.BlobHash == f.BlobHash.String() {
 				// No change; do nothing.
 				continue
 			}
 			added, err := u.handleCVE(f, old, tx)
 			if err != nil {
 				return err
 			}
 			if added {
 				numAdds++
 			} else {
 				numMods++
 			}
 		}
 		return nil
 	})
 	if err != nil {
 		return 0, 0, err
 	}
 	log.Debugf(ctx, "update transaction %s=%s: added %d, modified %d", startID, endID, numAdds, numMods)
 	return numAdds, numMods, nil
 }

 // handleCVE determines how to change the store for a single CVE.
 // The CVE will definitely be either added, if it's new, or modified, if it's
 // already in the DB.
 func (u *cveUpdater) handleCVE(f cvelistrepo.File, old *store.CVERecord, tx store.Transaction) (added bool, err error) {
 	defer derrors.Wrap(&err, "handleCVE(%s)", f.Filename)
 	cve, err := cvelistrepo.ParseCVE(u.repo, f)
 	if err != nil {
 		return false, err
 	}
 	var result *triageResult
 	if cve.State == cveschema.StatePublic && !u.knownIDs[cve.ID] {
 		c := cve
 		// If a false positive has changed, we only care about
 		// whether new reference URLs refer to a Go module.
 		// We know some old ones do. So remove the old ones
 		// before checking.
 		if old != nil && old.TriageState == store.TriageStateFalsePositive {
 			c = copyRemoving(cve, old.ReferenceURLs)
 		}
 		result, err = u.affectedModule(c)
 		if err != nil {
 			return false, err
 		}
 	}

 	pathname := path.Join(f.DirPath, f.Filename)
 	// If the CVE is not in the database, add it.
 	if old == nil {
 		cr := store.NewCVERecord(cve, pathname, f.BlobHash.String(), u.commit)
 		switch {
 		case result != nil:
 			cr.TriageState = store.TriageStateNeedsIssue
 			cr.Module = result.modulePath
 			cr.Package = result.packagePath
 			cr.TriageStateReason = result.reason
 			cr.CVE = cve
 		case u.knownIDs[cve.ID]:
 			cr.TriageState = store.TriageStateHasVuln
 		default:
 			cr.TriageState = store.TriageStateNoActionNeeded
 		}
 		if err := tx.CreateCVERecord(cr); err != nil {
 			return false, err
 		}
 		return true, nil
 	}
 	// Change to an existing record.
 	mod := *old // copy the old one
 	mod.Path = pathname
 	mod.BlobHash = f.BlobHash.String()
 	mod.CVEState = cve.State
 	mod.CommitHash = u.commit.Hash.String()
 	mod.CommitTime = u.commit.Committer.When.In(time.UTC)
 	switch old.TriageState {
 	case store.TriageStateNoActionNeeded, store.TriageStateFalsePositive:
 		if result != nil {
 			// Didn't need an issue before, does now.
 			mod.TriageState = store.TriageStateNeedsIssue
 			mod.Module = result.modulePath
 			mod.Package = result.packagePath
 			mod.TriageStateReason = result.reason
 			mod.CVE = cve
 		}
 		// Else don't change the triage state, but we still want
 		// to update the other changed fields.

 	case store.TriageStateNeedsIssue:
 		if result == nil {
 			// Needed an issue, no longer does.
 			mod.TriageState = store.TriageStateNoActionNeeded
 			mod.Module = ""
 			mod.CVE = nil
 		}
 		// Else don't change the triage state, but we still want
 		// to update the other changed fields.

 	case store.TriageStateIssueCreated, store.TriageStateUpdatedSinceIssueCreation:
 		// An issue was filed, so a person should revisit this CVE.
 		mod.TriageState = store.TriageStateUpdatedSinceIssueCreation
 		var mp string
 		if result != nil {
 			mp = result.modulePath
 		}
 		mod.TriageStateReason = fmt.Sprintf("CVE changed; affected module = %q", mp)
 	case store.TriageStateHasVuln:
 		// There is already a Go vuln report for this CVE, so
 		// nothing to do.
 	default:
 		return false, fmt.Errorf("unknown TriageState: %q", old.TriageState)
 	}
 	// If the triage state changed, add the old state to the history at the beginning.
 	if old.TriageState != mod.TriageState {
 		mod.History = append([]*store.CVERecordSnapshot{old.Snapshot()}, mod.History...)
 	}
 	// If we're here, then mod is a modification to the DB.
 	if err := tx.SetCVERecord(&mod); err != nil {
 		return false, err
 	}
 	if mod.TriageState == store.TriageStateNeedsIssue && mod.CVE == nil {
 		return false, errors.New("needs issue but CVE is nil")
 	}
 	return false, nil
 }

 // copyRemoving returns a copy of cve with any reference that has a given URL removed.
 func copyRemoving(cve *cveschema.CVE, refURLs []string) *cveschema.CVE {
 	remove := map[string]bool{}
 	for _, u := range refURLs {
 		remove[u] = true
 	}
 	c := *cve
 	var rs []cveschema.Reference
 	for _, r := range cve.References.Data {
 		if !remove[r.URL] {
 			rs = append(rs, r)
 		}
 	}
 	c.References.Data = rs
 	return &c
 }

 // Collect files by directory, verifying that directories are contiguous in
 // the list of files. Our directory hash optimization depends on that.
 func groupFilesByDirectory(files []cvelistrepo.File) ([][]cvelistrepo.File, error) {
 	if len(files) == 0 {
 		return nil, nil
 	}
 	var (
 		result [][]cvelistrepo.File
 		curDir []cvelistrepo.File
 	)
 	for _, f := range files {
 		if len(curDir) > 0 && f.DirPath != curDir[0].DirPath {
 			result = append(result, curDir)
 			curDir = nil
 		}
 		curDir = append(curDir, f)
 	}
 	if len(curDir) > 0 {
 		result = append(result, curDir)
 	}
 	seen := map[string]bool{}
 	for _, dir := range result {
 		if seen[dir[0].DirPath] {
 			return nil, fmt.Errorf("directory %s is not contiguous in the sorted list of files", dir[0].DirPath)
 		}
 		seen[dir[0].DirPath] = true
 	}
 	return result, nil
 }

 // idFromFilename extracts the CVE ID from  a filename.
 func idFromFilename(name string) string {
 	return strings.TrimSuffix(path.Base(name), path.Ext(name))
 }

 type UpdateGHSAStats struct {
 	// Number of GitHub security advisories seen.
 	NumProcessed int
 	// Number of GHSARecords added to the store.
 	NumAdded int
 	// Number of GHSARecords already in the store that were modified.
 	NumModified int
 }

 func updateGHSAs(ctx context.Context, listSAs GHSAListFunc, since time.Time, st store.Store) (stats UpdateGHSAStats, err error) {
 	defer derrors.Wrap(&err, "updateGHSAs(%s)", since)
 	ctx = event.Start(ctx, "updateGHSAs")
 	defer event.End(ctx)

 	defer func() {
 		if err != nil {
 			log.Errorf(ctx, "GHSA update failed: %v", err)
 		} else {
 			log.Infof(ctx, "GHSA update succeeded with since=%s: %+v", since, stats)
 		}
 	}()

 	log.Infof(ctx, "GHSA update starting with since=%s", since)

 	// Get all of the GHSAs since the given time from GitHub.
 	sas, err := listSAs(ctx, since)
 	if err != nil {
 		return stats, err
 	}
 	stats.NumProcessed = len(sas)
 	if len(sas) > maxTransactionWrites {
 		return stats, errors.New("number of advisories exceeds maxTransactionWrites")
 	}
 	numAdded := 0
 	numModified := 0
 	err = st.RunTransaction(ctx, func(ctx context.Context, tx store.Transaction) error {
 		numAdded = 0
 		numModified = 0
 		// Read the existing records from the store.
 		sars, err := tx.GetGHSARecords()
 		if err != nil {
 			return err
 		}
 		idToRecord := map[string]*store.GHSARecord{}
 		for _, r := range sars {
 			idToRecord[r.GHSA.ID] = r
 		}

 		// Determine what needs to be added and modified.
 		for _, sa := range sas {
 			old := idToRecord[sa.ID]
 			if old == nil {
 				// Add record.
 				r := &store.GHSARecord{
 					GHSA: sa,
 					// All new records need an issue, since ghsa.List already
 					// filters for vulns in the Go ecosystem.
 					TriageState: store.TriageStateNeedsIssue,
 				}
 				if err := tx.CreateGHSARecord(r); err != nil {
 					return err
 				}
 				numAdded++
 			} else if !old.GHSA.UpdatedAt.Equal(sa.UpdatedAt) {
 				// Modify record.
 				mod := *old
 				mod.GHSA = sa
 				switch old.TriageState {
 				case store.TriageStateNoActionNeeded:
 					mod.TriageState = store.TriageStateNeedsIssue
 					mod.TriageStateReason = "advisory was updated"
 				case store.TriageStateIssueCreated:
 					mod.TriageState = store.TriageStateUpdatedSinceIssueCreation
 				default:
 					// Don't change the TriageState.
 				}
 				if err := tx.SetGHSARecord(&mod); err != nil {
 					return err
 				}
 				numModified++
 			}
 		}
 		return nil
 	})
 	stats.NumAdded = numAdded
 	stats.NumModified = numModified
 	return stats, nil
 }
	// Copyright 2021 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package worker

	import (
	"context"
	"errors"
	"fmt"
	"path"
	"strings"
	"time"

	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing/object"
	"golang.org/x/exp/event"
	"golang.org/x/vulndb/internal/cvelistrepo"
	"golang.org/x/vulndb/internal/cveschema"
	"golang.org/x/vulndb/internal/derrors"
	"golang.org/x/vulndb/internal/worker/log"
	"golang.org/x/vulndb/internal/worker/store"
	)

	// A triageFunc triages a CVE: it decides whether an issue needs to be filed.
	// If so, it returns a non-empty string indicating the possibly
	// affected module.
	type triageFunc func(cveschema.CVE) (triageResult, error)

	// A cveUpdater performs an update operation on the DB.
	type cveUpdater struct {
	repo *git.Repository
	commit *object.Commit
	st store.Store
	knownIDs map[string]bool
	affectedModule triageFunc
	}

	type updateStats struct {
	skipped bool // directory skipped because hashes match
	numProcessed, numAdded, numModified int
	}

	// newCVEUpdater creates an updater for updating the store with information from
	// the repo commit.
	// needsIssue determines whether a CVE needs an issue to be filed for it.
	func newCVEUpdater(repo git.Repository, commit object.Commit, st store.Store, knownVulnIDs []string, needsIssue triageFunc) *cveUpdater {
	u := &cveUpdater{
	repo: repo,
	commit: commit,
	st: st,
	knownIDs: map[string]bool{},
	affectedModule: needsIssue,
	}
	for _, k := range knownVulnIDs {
	u.knownIDs[k] = true
	}
	return u
	}

	// update updates the DB to match the repo at the given commit.
	// It also triages new or changed issues.
	func (u cveUpdater) update(ctx context.Context) (ur store.CommitUpdateRecord, err error) {
	// We want the action of reading the old DB record, updating it and
	// writing it back to be atomic. It would be too expensive to do that one
	// record at a time. Ideally we'd process the whole repo commit in one
	// transaction, but Firestore has a limit on how many writes one
	// transaction can do, so the CVE files in the repo are processed in
	// batches, one transaction per batch.
	defer derrors.Wrap(&err, "cveUpdater.update(%s)", u.commit.Hash)
	ctx = event.Start(ctx, "cveUpdater.update")
	defer event.End(ctx)

	defer func() {
	if err != nil {
	log.Errorf(ctx, "update failed: %v", err)
	} else {
	var nAdded, nModified int64
	if ur != nil {
	nAdded = int64(ur.NumAdded)
	nModified = int64(ur.NumModified)
	}
	log.Infof(ctx, "update succeeded on %s: added %d, modified %d",
	u.commit.Hash, nAdded, nModified)
	}
	}()

	log.Infof(ctx, "CVE update starting on %s", u.commit.Hash)

	// Get all the CVE files.
	// It is cheaper to read all the files from the repo and compare
	// them to the DB in bulk, than to walk the repo and process
	// each file individually.
	files, err := cvelistrepo.Files(u.repo, u.commit)
	if err != nil {
	return nil, err
	}
	// Process files in the same directory together, so we can easily skip
	// the entire directory if it hasn't changed.
	filesByDir, err := groupFilesByDirectory(files)
	if err != nil {
	return nil, err
	}

	// Create a new CommitUpdateRecord to describe this run of doUpdate.
	ur = &store.CommitUpdateRecord{
	StartedAt: time.Now(),
	CommitHash: u.commit.Hash.String(),
	CommitTime: u.commit.Committer.When,
	NumTotal: len(files),
	}
	if err := u.st.CreateCommitUpdateRecord(ctx, ur); err != nil {
	return ur, err
	}

	var skippedDirs []string
	const logSkippedEvery = 20 // Log a message every this many skipped directories.
	for _, dirFiles := range filesByDir {
	stats, err := u.updateDirectory(ctx, dirFiles)
	// Change the CommitUpdateRecord in the Store to reflect the results of the directory update.
	if err != nil {
	ur.Error = err.Error()
	if err2 := u.st.SetCommitUpdateRecord(ctx, ur); err2 != nil {
	return ur, fmt.Errorf("update failed with %w, could not set update record: %v", err, err2)
	}
	}
	if stats.skipped {
	skippedDirs = append(skippedDirs, dirFiles[0].DirPath)
	if len(skippedDirs) >= logSkippedEvery {
	log.Infof(ctx, "skipping directory %s and %d others because the hashes match",
	skippedDirs[0], len(skippedDirs)-1)
	skippedDirs = nil
	}
	}
	ur.NumProcessed += stats.numProcessed
	ur.NumAdded += stats.numAdded
	ur.NumModified += stats.numModified
	if err := u.st.SetCommitUpdateRecord(ctx, ur); err != nil {
	return ur, err
	}
	}
	ur.EndedAt = time.Now()
	return ur, u.st.SetCommitUpdateRecord(ctx, ur)
	}

	// Firestore supports a maximum of 500 writes per transaction.
	// See https://cloud.google.com/firestore/quotas.
	const maxTransactionWrites = 500

	func (u *cveUpdater) updateDirectory(ctx context.Context, dirFiles []cvelistrepo.File) (_ updateStats, err error) {
	dirPath := dirFiles[0].DirPath
	dirHash := dirFiles[0].TreeHash.String()

	// A non-empty directory hash means that we have fully processed the directory
	// with that hash. If the stored hash matches the current one, we can skip
	// this directory.
	dbHash, err := u.st.GetDirectoryHash(ctx, dirPath)
	if err != nil {
	return updateStats{}, err
	}
	if dirHash == dbHash {
	return updateStats{skipped: true}, nil
	}
	// Set the hash to something that can't match, until we fully process this directory.
	if err := u.st.SetDirectoryHash(ctx, dirPath, "in progress"); err != nil {
	return updateStats{}, err
	}
	// It's okay if we crash now; the directory hashes are just an optimization.
	// At worst we'll redo this directory next time.

	// Update files in batches.

	var stats updateStats
	for i := 0; i < len(dirFiles); i += maxTransactionWrites {
	j := i + maxTransactionWrites
	if j > len(dirFiles) {
	j = len(dirFiles)
	}
	numBatchAdds, numBatchMods, err := u.updateBatch(ctx, dirFiles[i:j])
	if err != nil {
	return updateStats{}, err
	}
	stats.numProcessed += j - i
	// Add in these two numbers here, instead of in the function passed to
	// RunTransaction, because that function may be executed multiple times.
	stats.numAdded += numBatchAdds
	stats.numModified += numBatchMods
	} // end batch loop

	// We're done with this directory, so we can remember its hash.
	if err := u.st.SetDirectoryHash(ctx, dirPath, dirHash); err != nil {
	return updateStats{}, err
	}
	return stats, nil
	}

	func (u *cveUpdater) updateBatch(ctx context.Context, batch []cvelistrepo.File) (numAdds, numMods int, err error) {
	startID := idFromFilename(batch[0].Filename)
	endID := idFromFilename(batch[len(batch)-1].Filename)
	defer derrors.Wrap(&err, "updateBatch(%s-%s)", startID, endID)

	err = u.st.RunTransaction(ctx, func(ctx context.Context, tx store.Transaction) error {
	numAdds = 0
	numMods = 0

	// Read information about the existing state in the store that's
	// relevant to this batch. Since the entries are sorted, we can read
	// a range of IDS.
	crs, err := tx.GetCVERecords(startID, endID)
	if err != nil {
	return err
	}
	idToRecord := map[string]*store.CVERecord{}
	for _, cr := range crs {
	idToRecord[cr.ID] = cr
	}
	// Determine what needs to be added and modified.
	for _, f := range batch {
	id := idFromFilename(f.Filename)
	old := idToRecord[id]
	if old != nil && old.BlobHash == f.BlobHash.String() {
	// No change; do nothing.
	continue
	}
	added, err := u.handleCVE(f, old, tx)
	if err != nil {
	return err
	}
	if added {
	numAdds++
	} else {
	numMods++
	}
	}
	return nil
	})
	if err != nil {
	return 0, 0, err
	}
	log.Debugf(ctx, "update transaction %s=%s: added %d, modified %d", startID, endID, numAdds, numMods)
	return numAdds, numMods, nil
	}

	// handleCVE determines how to change the store for a single CVE.
	// The CVE will definitely be either added, if it's new, or modified, if it's
	// already in the DB.
	func (u cveUpdater) handleCVE(f cvelistrepo.File, old store.CVERecord, tx store.Transaction) (added bool, err error) {
	defer derrors.Wrap(&err, "handleCVE(%s)", f.Filename)
	cve, err := cvelistrepo.ParseCVE(u.repo, f)
	if err != nil {
	return false, err
	}
	var result *triageResult
	if cve.State == cveschema.StatePublic && !u.knownIDs[cve.ID] {
	c := cve
	// If a false positive has changed, we only care about
	// whether new reference URLs refer to a Go module.
	// We know some old ones do. So remove the old ones
	// before checking.
	if old != nil && old.TriageState == store.TriageStateFalsePositive {
	c = copyRemoving(cve, old.ReferenceURLs)
	}
	result, err = u.affectedModule(c)
	if err != nil {
	return false, err
	}
	}

	pathname := path.Join(f.DirPath, f.Filename)
	// If the CVE is not in the database, add it.
	if old == nil {
	cr := store.NewCVERecord(cve, pathname, f.BlobHash.String(), u.commit)
	switch {
	case result != nil:
	cr.TriageState = store.TriageStateNeedsIssue
	cr.Module = result.modulePath
	cr.Package = result.packagePath
	cr.TriageStateReason = result.reason
	cr.CVE = cve
	case u.knownIDs[cve.ID]:
	cr.TriageState = store.TriageStateHasVuln
	default:
	cr.TriageState = store.TriageStateNoActionNeeded
	}
	if err := tx.CreateCVERecord(cr); err != nil {
	return false, err
	}
	return true, nil
	}
	// Change to an existing record.
	mod := *old // copy the old one
	mod.Path = pathname
	mod.BlobHash = f.BlobHash.String()
	mod.CVEState = cve.State
	mod.CommitHash = u.commit.Hash.String()
	mod.CommitTime = u.commit.Committer.When.In(time.UTC)
	switch old.TriageState {
	case store.TriageStateNoActionNeeded, store.TriageStateFalsePositive:
	if result != nil {
	// Didn't need an issue before, does now.
	mod.TriageState = store.TriageStateNeedsIssue
	mod.Module = result.modulePath
	mod.Package = result.packagePath
	mod.TriageStateReason = result.reason
	mod.CVE = cve
	}
	// Else don't change the triage state, but we still want
	// to update the other changed fields.

	case store.TriageStateNeedsIssue:
	if result == nil {
	// Needed an issue, no longer does.
	mod.TriageState = store.TriageStateNoActionNeeded
	mod.Module = ""
	mod.CVE = nil
	}
	// Else don't change the triage state, but we still want
	// to update the other changed fields.

	case store.TriageStateIssueCreated, store.TriageStateUpdatedSinceIssueCreation:
	// An issue was filed, so a person should revisit this CVE.
	mod.TriageState = store.TriageStateUpdatedSinceIssueCreation
	var mp string
	if result != nil {
	mp = result.modulePath
	}
	mod.TriageStateReason = fmt.Sprintf("CVE changed; affected module = %q", mp)
	case store.TriageStateHasVuln:
	// There is already a Go vuln report for this CVE, so
	// nothing to do.
	default:
	return false, fmt.Errorf("unknown TriageState: %q", old.TriageState)
	}
	// If the triage state changed, add the old state to the history at the beginning.
	if old.TriageState != mod.TriageState {
	mod.History = append([]*store.CVERecordSnapshot{old.Snapshot()}, mod.History...)
	}
	// If we're here, then mod is a modification to the DB.
	if err := tx.SetCVERecord(&mod); err != nil {
	return false, err
	}
	if mod.TriageState == store.TriageStateNeedsIssue && mod.CVE == nil {
	return false, errors.New("needs issue but CVE is nil")
	}
	return false, nil
	}

	// copyRemoving returns a copy of cve with any reference that has a given URL removed.
	func copyRemoving(cve cveschema.CVE, refURLs []string) cveschema.CVE {
	remove := map[string]bool{}
	for _, u := range refURLs {
	remove[u] = true
	}
	c := *cve
	var rs []cveschema.Reference
	for _, r := range cve.References.Data {
	if !remove[r.URL] {
	rs = append(rs, r)
	}
	}
	c.References.Data = rs
	return &c
	}

	// Collect files by directory, verifying that directories are contiguous in
	// the list of files. Our directory hash optimization depends on that.
	func groupFilesByDirectory(files []cvelistrepo.File) ([][]cvelistrepo.File, error) {
	if len(files) == 0 {
	return nil, nil
	}
	var (
	result [][]cvelistrepo.File
	curDir []cvelistrepo.File
	)
	for _, f := range files {
	if len(curDir) > 0 && f.DirPath != curDir[0].DirPath {
	result = append(result, curDir)
	curDir = nil
	}
	curDir = append(curDir, f)
	}
	if len(curDir) > 0 {
	result = append(result, curDir)
	}
	seen := map[string]bool{}
	for _, dir := range result {
	if seen[dir[0].DirPath] {
	return nil, fmt.Errorf("directory %s is not contiguous in the sorted list of files", dir[0].DirPath)
	}
	seen[dir[0].DirPath] = true
	}
	return result, nil
	}

	// idFromFilename extracts the CVE ID from a filename.
	func idFromFilename(name string) string {
	return strings.TrimSuffix(path.Base(name), path.Ext(name))
	}

	type UpdateGHSAStats struct {
	// Number of GitHub security advisories seen.
	NumProcessed int
	// Number of GHSARecords added to the store.
	NumAdded int
	// Number of GHSARecords already in the store that were modified.
	NumModified int
	}

	func updateGHSAs(ctx context.Context, listSAs GHSAListFunc, since time.Time, st store.Store) (stats UpdateGHSAStats, err error) {
	defer derrors.Wrap(&err, "updateGHSAs(%s)", since)
	ctx = event.Start(ctx, "updateGHSAs")
	defer event.End(ctx)

	defer func() {
	if err != nil {
	log.Errorf(ctx, "GHSA update failed: %v", err)
	} else {
	log.Infof(ctx, "GHSA update succeeded with since=%s: %+v", since, stats)
	}
	}()

	log.Infof(ctx, "GHSA update starting with since=%s", since)

	// Get all of the GHSAs since the given time from GitHub.
	sas, err := listSAs(ctx, since)
	if err != nil {
	return stats, err
	}
	stats.NumProcessed = len(sas)
	if len(sas) > maxTransactionWrites {
	return stats, errors.New("number of advisories exceeds maxTransactionWrites")
	}
	numAdded := 0
	numModified := 0
	err = st.RunTransaction(ctx, func(ctx context.Context, tx store.Transaction) error {
	numAdded = 0
	numModified = 0
	// Read the existing records from the store.
	sars, err := tx.GetGHSARecords()
	if err != nil {
	return err
	}
	idToRecord := map[string]*store.GHSARecord{}
	for _, r := range sars {
	idToRecord[r.GHSA.ID] = r
	}

	// Determine what needs to be added and modified.
	for _, sa := range sas {
	old := idToRecord[sa.ID]
	if old == nil {
	// Add record.
	r := &store.GHSARecord{
	GHSA: sa,
	// All new records need an issue, since ghsa.List already
	// filters for vulns in the Go ecosystem.
	TriageState: store.TriageStateNeedsIssue,
	}
	if err := tx.CreateGHSARecord(r); err != nil {
	return err
	}
	numAdded++
	} else if !old.GHSA.UpdatedAt.Equal(sa.UpdatedAt) {
	// Modify record.
	mod := *old
	mod.GHSA = sa
	switch old.TriageState {
	case store.TriageStateNoActionNeeded:
	mod.TriageState = store.TriageStateNeedsIssue
	mod.TriageStateReason = "advisory was updated"
	case store.TriageStateIssueCreated:
	mod.TriageState = store.TriageStateUpdatedSinceIssueCreation
	default:
	// Don't change the TriageState.
	}
	if err := tx.SetGHSARecord(&mod); err != nil {
	return err
	}
	numModified++
	}
	}
	return nil
	})
	stats.NumAdded = numAdded
	stats.NumModified = numModified
	return stats, nil
	}