fix: user passwords cleanup (#1202)

1. Adds benchmarks comparing bcrypt and our pbkdf2 settings
1. Changes the pbkdf2 hash iterations back to 65k. 1024 is insecure
1. Gets rid of the short circuit when the user isn't found, preventing
   timing attacks which can reveal which emails exist on a deployment

```
$ go test -bench .
goos: linux
goarch: amd64
pkg: github.com/coder/coder/coderd/userpassword
cpu: Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz
BenchmarkBcryptMinCost-16        	    1651	    702727 ns/op	    5165 B/op      10 allocs/op
BenchmarkPbkdf2MinCost-16        	    1669	    714843 ns/op	     804 B/op      10 allocs/op
BenchmarkBcryptDefaultCost-16    	      27	  42676316 ns/op	    5246 B/op      10 allocs/op
BenchmarkPbkdf2-16               	      26	  45902236 ns/op	     804 B/op      10 allocs/op
PASS
ok  	github.com/coder/coder/coderd/userpassword	5.036s
```

coderd/userpassword/hashing_bench_test.go

@@ -0,0 +1,70 @@
+package userpassword_test
+
+import (
+	"crypto/sha256"
+	"testing"
+
+	"github.com/coder/coder/cryptorand"
+	"golang.org/x/crypto/bcrypt"
+	"golang.org/x/crypto/pbkdf2"
+)
+
+var (
+	salt   = []byte(must(cryptorand.String(16)))
+	secret = []byte(must(cryptorand.String(24)))
+
+	resBcrypt []byte
+	resPbkdf2 []byte
+)
+
+func BenchmarkBcryptMinCost(b *testing.B) {
+	var r []byte
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		r, _ = bcrypt.GenerateFromPassword(secret, bcrypt.MinCost)
+	}
+
+	resBcrypt = r
+}
+
+func BenchmarkPbkdf2MinCost(b *testing.B) {
+	var r []byte
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		r = pbkdf2.Key(secret, salt, 1024, 64, sha256.New)
+	}
+
+	resPbkdf2 = r
+}
+
+func BenchmarkBcryptDefaultCost(b *testing.B) {
+	var r []byte
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		r, _ = bcrypt.GenerateFromPassword(secret, bcrypt.DefaultCost)
+	}
+
+	resBcrypt = r
+}
+
+func BenchmarkPbkdf2(b *testing.B) {
+	var r []byte
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		r = pbkdf2.Key(secret, salt, 65536, 64, sha256.New)
+	}
+
+	resPbkdf2 = r
+}
+
+func must(s string, err error) string {
+	if err != nil {
+		panic(err)
+	}
+
+	return s
+}

coderd/userpassword/userpassword.go

@@ -6,25 +6,67 @@ import (
 	"crypto/subtle"
 	"encoding/base64"
 	"fmt"
+	"os"
 	"strconv"
 	"strings"
 
 	"golang.org/x/crypto/pbkdf2"
+	"golang.org/x/exp/slices"
 	"golang.org/x/xerrors"
 )
 
-const (
-	// This is the length of our output hash.
-	// bcrypt has a hash size of 59, so we rounded up to a power of 8.
+var (
+	// The base64 encoder used when producing the string representation of
+	// hashes.
+	base64Encoding = base64.RawStdEncoding
+
+	// The number of iterations to use when generating the hash. This was chosen
+	// to make it about as fast as bcrypt hashes. Increasing this causes hashes
+	// to take longer to compute.
+	defaultHashIter = 65535
+
+	// This is the length of our output hash. bcrypt has a hash size of up to
+	// 60, so we rounded up to a power of 8.
 	hashLength = 64
+
 	// The scheme to include in our hashed password.
 	hashScheme = "pbkdf2-sha256"
+
+	// A salt size of 16 is the default in passlib. A minimum of 8 can be safely
+	// used.
+	defaultSaltSize = 16
+
+	// The simulated hash is used when trying to simulate password checks for
+	// users that don't exist.
+	simulatedHash, _ = Hash("hunter2")
 )
 
-// Compare checks the equality of passwords from a hashed pbkdf2 string.
-// This uses pbkdf2 to ensure FIPS 140-2 compliance. See:
+// Make password hashing much faster in tests.
+func init() {
+	args := os.Args[1:]
+
+	// Ensure this can never be enabled if running in server mode.
+	if slices.Contains(args, "server") {
+		return
+	}
+
+	for _, flag := range args {
+		if strings.HasPrefix(flag, "-test.") {
+			defaultHashIter = 1
+			return
+		}
+	}
+}
+
+// Compare checks the equality of passwords from a hashed pbkdf2 string. This
+// uses pbkdf2 to ensure FIPS 140-2 compliance. See:
 // https://csrc.nist.gov/csrc/media/templates/cryptographic-module-validation-program/documents/security-policies/140sp2261.pdf
 func Compare(hashed string, password string) (bool, error) {
+	// If the hased password provided is empty, simulate comparing a real hash.
+	if hashed == "" {
+		hashed = simulatedHash
+	}
+
 	if len(hashed) < hashLength {
 		return false, xerrors.Errorf("hash too short: %d", len(hashed))
 	}
@@ -42,7 +84,7 @@ func Compare(hashed string, password string) (bool, error) {
 	if err != nil {
 		return false, xerrors.Errorf("parse iter from hash: %w", err)
 	}
-	salt, err := base64.RawStdEncoding.DecodeString(parts[3])
+	salt, err := base64Encoding.DecodeString(parts[3])
 	if err != nil {
 		return false, xerrors.Errorf("decode salt: %w", err)
 	}
@@ -50,29 +92,32 @@ func Compare(hashed string, password string) (bool, error) {
 	if subtle.ConstantTimeCompare([]byte(hashWithSaltAndIter(password, salt, iter)), []byte(hashed)) != 1 {
 		return false, nil
 	}
+
 	return true, nil
 }
 
 // Hash generates a hash using pbkdf2.
 // See the Compare() comment for rationale.
 func Hash(password string) (string, error) {
-	// bcrypt uses a salt size of 16 bytes.
-	salt := make([]byte, 16)
+	salt := make([]byte, defaultSaltSize)
 	_, err := rand.Read(salt)
 	if err != nil {
 		return "", xerrors.Errorf("read random bytes for salt: %w", err)
 	}
-	// The default hash iteration is 1024 for speed.
-	// As this is increased, the password is hashed more.
-	return hashWithSaltAndIter(password, salt, 1024), nil
+
+	return hashWithSaltAndIter(password, salt, defaultHashIter), nil
 }
 
 // Produces a string representation of the hash.
 func hashWithSaltAndIter(password string, salt []byte, iter int) string {
-	hash := pbkdf2.Key([]byte(password), salt, iter, hashLength, sha256.New)
-	hash = []byte(base64.RawStdEncoding.EncodeToString(hash))
-	salt = []byte(base64.RawStdEncoding.EncodeToString(salt))
-	// This format is similar to bcrypt. See:
-	// https://en.wikipedia.org/wiki/Bcrypt#Description
-	return fmt.Sprintf("$%s$%d$%s$%s", hashScheme, iter, salt, hash)
+	var (
+		hash    = pbkdf2.Key([]byte(password), salt, iter, hashLength, sha256.New)
+		encHash = make([]byte, base64Encoding.EncodedLen(len(hash)))
+		encSalt = make([]byte, base64Encoding.EncodedLen(len(salt)))
+	)
+
+	base64Encoding.Encode(encHash, hash)
+	base64Encoding.Encode(encSalt, salt)
+
+	return fmt.Sprintf("$%s$%d$%s$%s", hashScheme, iter, encSalt, encHash)
 }

coderd/users.go

@@ -461,21 +461,19 @@ func (api *api) postLogin(rw http.ResponseWriter, r *http.Request) {
 	if !httpapi.Read(rw, r, &loginWithPassword) {
 		return
 	}
+
 	user, err := api.Database.GetUserByEmailOrUsername(r.Context(), database.GetUserByEmailOrUsernameParams{
 		Email: loginWithPassword.Email,
 	})
-	if errors.Is(err, sql.ErrNoRows) {
-		httpapi.Write(rw, http.StatusUnauthorized, httpapi.Response{
-			Message: "invalid email or password",
-		})
-		return
-	}
-	if err != nil {
+	if err != nil && !xerrors.Is(err, sql.ErrNoRows) {
 		httpapi.Write(rw, http.StatusInternalServerError, httpapi.Response{
 			Message: fmt.Sprintf("get user: %s", err.Error()),
 		})
 		return
 	}
+
+	// If the user doesn't exist, it will be a default struct.
+
 	equal, err := userpassword.Compare(string(user.HashedPassword), loginWithPassword.Password)
 	if err != nil {
 		httpapi.Write(rw, http.StatusInternalServerError, httpapi.Response{