Say how to allow a refused private target address (closes #398)

Adding or editing an http or slack target whose address is private or
reserved was refused with no hint that the refusal is deliberate or
that it can be lifted. The refusal now adds that such addresses are
refused by default and that the server's ALLOWED_EGRESS_CIDRS setting
allows named networks, naming the README section "Allowing egress to
your own network". Metadata refusals do not get it: link-local and the
other unconditional metadata addresses cannot be opened, and Azure's
WireServer, which listing does open, serves VM credentials.

The delivery package refuses WireServer with its own error and exports
the private-or-reserved one as ErrBlockedIP, so the handler can tell
them apart.

Model: opus-5-5

README.md

@@ -157,21 +157,6 @@ public cloud metadata addresses: currently only `168.63.129.16`, Azure's
 WireServer, which serves an Azure VM its credentials. Because it is a
 public address, listing it in `ALLOWED_EGRESS_CIDRS` reopens it.
 
-That is all the default blocklist covers: the IPv4 private and reserved
-ranges; of IPv6, only loopback (`::1`), unique local addresses
-(`fc00::/7`) and link-local addresses (`fe80::/10`); and certain public
-addresses. A public address belongs on the default blocklist only if it
-hands credentials, user data or bootstrap material to whatever can reach
-it, without the caller presenting anything. A provider's other public
-addresses are not refused. IBM Cloud, for example, serves its package
-mirrors, time servers and object storage on `161.26.0.0/16`, and the
-private endpoints of its own cloud services on `166.8.0.0/14`. Neither
-range hands out credentials that way: the token service among those
-endpoints issues a token only in exchange for something the caller
-presents, such as an API key. Reaching these services can be a
-legitimate delivery, and every cloud has some, so a partial list would
-promise coverage it does not give.
-
 That default is also inconvenient for the thing webhooker is mostly
 for: taking a public webhook and forwarding it to something on your own
 network. A container on the same Docker network, a box on `10.x`, a

internal/database/export_test.go

@@ -5,7 +5,6 @@ import (
 	"io"
 	"log/slog"
 	"os"
-	"testing"
 	"time"
 
 	"go.uber.org/fx"
@@ -80,14 +79,3 @@ func (d *Database) ExportSetBannerOut(w io.Writer) {
 func DummyPasswordHashForTest() string {
 	return dummyPasswordHash()
 }
-
-// HashAtShippedCostForTest makes HashPassword hash at the shipped
-// memory cost until t ends. t must not run in parallel with other
-// tests, which would hash at that cost alongside it.
-func HashAtShippedCostForTest(t *testing.T) {
-	t.Helper()
-
-	hashAtShippedCostInTest = true
-
-	t.Cleanup(func() { hashAtShippedCostInTest = false })
-}

internal/database/password.go

@@ -9,7 +9,6 @@ import (
 	"math/big"
 	"strings"
 	"sync"
-	"testing"
 
 	"golang.org/x/crypto/argon2"
 )
@@ -64,30 +63,10 @@ func DefaultPasswordConfig() *PasswordConfig {
 	}
 }
 
-// testArgon2Memory is the Argon2id memory cost, in KiB, that a test
-// binary hashes with: 1 MB instead of the shipped 64 MB. Every test
-// that starts a database hashes the bootstrap admin password, dozens
-// of them run in parallel, and under the race detector each 64 MB hash
-// holds about 150 MB. VerifyPassword reads the cost from the hash it
-// checks, so verification follows.
-const testArgon2Memory = 1024
-
-// hashAtShippedCostInTest makes a test binary hash at the shipped
-// memory cost. Only TestHashPassword_ShippedParameters sets it.
-//
-//nolint:gochecknoglobals // set by one test, see above
-var hashAtShippedCostInTest bool
-
-// HashPassword generates an Argon2id hash of the password. A binary
-// built by go test hashes at testArgon2Memory; one built by go build
-// always hashes at the defaults.
+// HashPassword generates an Argon2id hash of the password
 func HashPassword(password string) (string, error) {
 	config := DefaultPasswordConfig()
 
-	if testing.Testing() && !hashAtShippedCostInTest {
-		config.Memory = testArgon2Memory
-	}
-
 	// Generate a salt
 	salt := make([]byte, config.SaltLen)
 

internal/database/password_test.go

@@ -192,39 +192,6 @@ func TestHashPasswordUniqueness(t *testing.T) {
 	}
 }
 
-// TestHashPassword_ShippedParameters hashes and verifies through
-// HashPassword at the shipped Argon2id parameters. Every other test
-// hashes at the lower memory cost a test binary uses, so this is the
-// one that keeps production hashing covered. One hash and one
-// verification: each costs 64 MB.
-//
-//nolint:paralleltest // changes the hashing cost for the whole binary
-func TestHashPassword_ShippedParameters(t *testing.T) {
-	database.HashAtShippedCostForTest(t)
-
-	password := "correct horse battery staple"
-
-	hash, err := database.HashPassword(password)
-	if err != nil {
-		t.Fatalf("hashing with the shipped parameters: %v", err)
-	}
-
-	const shipped = "$argon2id$v=19$m=65536,t=1,p=4$"
-
-	if !strings.HasPrefix(hash, shipped) {
-		t.Errorf("hash = %q, want prefix %q", hash, shipped)
-	}
-
-	valid, err := database.VerifyPassword(password, hash)
-	if err != nil {
-		t.Fatalf("VerifyPassword() error = %v", err)
-	}
-
-	if !valid {
-		t.Error("VerifyPassword() returned false for correct password")
-	}
-}
-
 // TestVerifyDummyPassword_DoesRealWork covers the anti-enumeration
 // path. Login charges an unknown username a verification against a
 // dummy hash so that a nonexistent account is not answered in

internal/delivery/ssrf.go

@@ -17,6 +17,10 @@ const (
 	// dnsResolutionTimeout is the maximum time to wait for
 	// DNS resolution during SSRF validation.
 	dnsResolutionTimeout = 5 * time.Second
+
+	// azureWireServer is Azure's WireServer, a public address that
+	// serves VM credentials.
+	azureWireServer = "168.63.129.16"
 )
 
 // Sentinel errors for SSRF validation.
@@ -25,8 +29,14 @@ var (
 	errNoIPs      = errors.New(
 		"hostname resolved to no IP addresses",
 	)
-	errBlockedIP = errors.New(
-		"blocked private, reserved or cloud metadata address",
+	// ErrBlockedIP reports a private or reserved address the
+	// default blocklist refuses, one that ALLOWED_EGRESS_CIDRS
+	// can open.
+	ErrBlockedIP = errors.New(
+		"blocked private or reserved address",
+	)
+	errBlockedWireServer = errors.New(
+		"blocked cloud metadata address",
 	)
 	errBlockedMetadata = errors.New(
 		"blocked link-local or cloud instance metadata " +
@@ -43,13 +53,6 @@ var (
 // permit specific blocks out of this set with
 // ALLOWED_EGRESS_CIDRS; see Guard.
 //
-// A public address belongs on the default blocklist only if it
-// hands credentials, user data or bootstrap material to whatever
-// can reach it, without the caller presenting anything. A
-// provider's other public addresses are not refused, since
-// reaching them can be legitimate and no list of them could be
-// complete.
-//
 //nolint:gochecknoglobals // package-level network list is appropriate here
 var blockedNetworks []*net.IPNet
 
@@ -130,8 +133,7 @@ func init() {
 		"::1/128",
 		"fc00::/7",
 		"fe80::/10",
-		// Azure WireServer, a public address that serves VM credentials.
-		"168.63.129.16/32",
+		azureWireServer + "/32",
 	})
 
 	// Every entry is named. The set must not grow or shrink
@@ -345,9 +347,17 @@ func (g *Guard) checkIP(ip net.IP) error {
 		return nil
 	}
 
+	// WireServer is on the default blocklist but is a public
+	// address, so its refusal does not call it private or reserved.
+	if ip.Equal(net.ParseIP(azureWireServer)) {
+		return fmt.Errorf(
+			"target IP %s: %w", ip, errBlockedWireServer,
+		)
+	}
+
 	if isBlockedIP(ip) {
 		return fmt.Errorf(
-			"target IP %s: %w", ip, errBlockedIP,
+			"target IP %s: %w", ip, ErrBlockedIP,
 		)
 	}
 

internal/handlers/source_management.go

@@ -1577,11 +1577,22 @@ func (h *Handlers) validateTargetURL(
 			"url", delivery.MaskURL(targetURL),
 			"error", err,
 		)
-		http.Error(
-			w,
-			"Invalid target URL: "+err.Error(),
-			http.StatusBadRequest,
-		)
+
+		msg := "Invalid target URL: " + err.Error()
+
+		// Only a private or reserved address's refusal says how
+		// to allow it. Metadata refusals never do: link-local and
+		// the other unconditional metadata addresses cannot be
+		// opened, and Azure's WireServer, which listing does
+		// open, hands out VM credentials.
+		if errors.Is(err, delivery.ErrBlockedIP) {
+			msg += ". Private and reserved addresses are refused " +
+				"by default; the server's ALLOWED_EGRESS_CIDRS " +
+				"setting allows named networks (see \"Allowing " +
+				"egress to your own network\" in the README)."
+		}
+
+		http.Error(w, msg, http.StatusBadRequest)
 
 		return err
 	}

internal/handlers/target_private_refusal_test.go

@@ -0,0 +1,116 @@
+package handlers_test
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// privateRefusalHint is the sentence that tells an operator a private
+// destination is refused on purpose, and how to allow one.
+const privateRefusalHint = "Private and reserved addresses are " +
+	"refused by default; the server's ALLOWED_EGRESS_CIDRS setting " +
+	"allows named networks (see \"Allowing egress to your own " +
+	"network\" in the README)."
+
+// TestTargetRefusal_PrivateDestinationSaysHowToAllowIt covers both
+// target types that take a URL, on add and on edit.
+func TestTargetRefusal_PrivateDestinationSaysHowToAllowIt(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	targetTypes := []database.TargetType{
+		database.TargetTypeHTTP,
+		database.TargetTypeSlack,
+	}
+
+	for _, targetType := range targetTypes {
+		t.Run(string(targetType), func(t *testing.T) {
+			t.Parallel()
+
+			webhook := seedWebhookWithRetention(t, env.db, 30)
+			targetsPath := "/source/" + webhook.ID + "/targets"
+
+			form := url.Values{}
+			form.Set("name", "private")
+			form.Set("type", string(targetType))
+			form.Set("url", editBlockedURL)
+
+			added := serveTarget(
+				env, http.MethodPost, targetsPath, form,
+			)
+			assert.Equal(t, http.StatusBadRequest, added.Code)
+			assert.Contains(
+				t, added.Body.String(), privateRefusalHint,
+			)
+
+			form.Set("url", editOriginalURL)
+
+			created := serveTarget(
+				env, http.MethodPost, targetsPath, form,
+			)
+			require.Equal(
+				t, http.StatusSeeOther, created.Code,
+				created.Body.String(),
+			)
+
+			targets := targetsForWebhook(t, env.db, webhook.ID)
+			require.Len(t, targets, 1)
+
+			form.Set("url", editBlockedURL)
+
+			edited := submitTargetEdit(
+				env, webhook.ID, targets[0].ID, form,
+			)
+			assert.Equal(t, http.StatusBadRequest, edited.Code)
+			assert.Contains(
+				t, edited.Body.String(), privateRefusalHint,
+			)
+		})
+	}
+}
+
+// TestTargetRefusal_MetadataDestinationDoesNotSayHowToAllowIt: no
+// setting opens a link-local address, and Azure's WireServer hands out
+// VM credentials, so neither refusal points at the setting.
+func TestTargetRefusal_MetadataDestinationDoesNotSayHowToAllowIt(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	metadataURLs := map[string]string{
+		"link-local": "http://169.254.169.254/latest/meta-data/",
+		"wireserver": "http://168.63.129.16/?comp=versions",
+	}
+
+	for name, metadataURL := range metadataURLs {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			webhook := seedWebhookWithRetention(t, env.db, 30)
+
+			form := url.Values{}
+			form.Set("name", "metadata")
+			form.Set("type", string(database.TargetTypeHTTP))
+			form.Set("url", metadataURL)
+
+			w := serveTarget(
+				env, http.MethodPost,
+				"/source/"+webhook.ID+"/targets", form,
+			)
+			assert.Equal(t, http.StatusBadRequest, w.Code)
+			assert.NotContains(
+				t, w.Body.String(), privateRefusalHint,
+			)
+		})
+	}
+}

internal/resetpw/resetpw_test.go

@@ -140,7 +140,7 @@ func (n *noopEvictor) EvictWebhook(string) {}
 // and the database, exactly as internal/handlers builds them.
 //
 // One application per test function, not per case: every start that
-// finds no account seeds one with an Argon2id hash, and this package's
+// finds no account seeds one at 64 MB of Argon2id, and this package's
 // budget is not the place to spend that repeatedly.
 func newServerApp(
 	t *testing.T, dir string,

script/test

@@ -22,11 +22,6 @@
 # The one figure above 90s is GOMAXPROCS 1, a synthetic core floor rather than
 # a condition CI runs under. If a CPU-limited runner ever puts a real run near
 # 67s, that is the datum to revisit the org figure with.
-#
-# -p 4 -parallel 8 keep the run under 2 GB of memory: at most four test
-# binaries build or run at once, each with at most eight parallel tests. Under
-# -race every test binary and every link costs a few hundred MB, so the
-# defaults (one per core) add up to several GB on a many-core host.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -34,7 +29,7 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 main() {
     cd "$ROOT"
     "$ROOT/script/assets"
-    go test -v -race -p 4 -parallel 8 -timeout 90s ./...
+    go test -v -race -timeout 90s ./...
 }
 
 main "$@"