internal/outcome: attempt nscd path-hiding if present

This avoids creating the mount point on musl setups which accomplishes nothing and can run into permission problems.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/env/env.go

@@ -1,21 +1,29 @@
-// Package env provides the [Paths] struct for efficiently building paths from the environment.
+// Package env provides the [Paths] struct for efficiently building paths from
+// the environment.
 package env
 
 import (
+	"errors"
+	"io/fs"
 	"log"
 	"os"
 	"strconv"
 
 	"hakurei.app/check"
+	"hakurei.app/fhs"
 	"hakurei.app/hst"
 )
 
+const VarRunNscd = fhs.Var + "run/nscd"
+
 // Paths holds paths copied from the environment and is used to create [hst.Paths].
 type Paths struct {
 	// TempDir is returned by [os.TempDir].
 	TempDir *check.Absolute
 	// RuntimePath is copied from $XDG_RUNTIME_DIR.
 	RuntimePath *check.Absolute
+	// Whether [VarRunNscd] is a directory.
+	HasNscd bool
 }
 
 // Copy expands [Paths] into [hst.Paths].
@@ -37,14 +45,17 @@ func (env *Paths) Copy(v *hst.Paths, userid int) {
 }
 
 // CopyPaths returns a populated [Paths].
-func CopyPaths() *Paths { return CopyPathsFunc(log.Fatalf, os.TempDir, os.Getenv) }
+func CopyPaths() *Paths {
+	return CopyPathsFunc(log.Fatalf, os.TempDir, os.Getenv, os.Stat)
+}
 
-// CopyPathsFunc returns a populated [Paths],
-// using the provided [log.Fatalf], [os.TempDir], [os.Getenv] functions.
+// CopyPathsFunc returns a populated [Paths], using the provided [log.Fatalf],
+// [os.TempDir], [os.Getenv] functions.
 func CopyPathsFunc(
 	fatalf func(format string, v ...any),
 	tempdir func() string,
 	getenv func(key string) string,
+	stat func(name string) (fs.FileInfo, error),
 ) *Paths {
 	const xdgRuntimeDir = "XDG_RUNTIME_DIR"
 
@@ -61,5 +72,14 @@ func CopyPathsFunc(
 		env.RuntimePath = a
 	}
 
+	if fi, err := stat(VarRunNscd); err != nil {
+		if !errors.Is(err, fs.ErrNotExist) {
+			fatalf("%v", err)
+			panic("unreachable")
+		}
+	} else {
+		env.HasNscd = fi.IsDir()
+	}
+
 	return &env
 }

internal/env/env_test.go

@@ -2,6 +2,7 @@ package env_test
 
 import (
 	"fmt"
+	"io/fs"
 	"reflect"
 	"testing"
 
@@ -104,7 +105,9 @@ func TestCopyPaths(t *testing.T) {
 					t.Fatalf("fatalf: %q, want %q", got, tc.fatal)
 				}
 				panic(stub.PanicExit)
-			}, func() string { return tc.tmp }, func(key string) string { return tc.env[key] })
+			}, func() string { return tc.tmp }, func(key string) string { return tc.env[key] }, func(name string) (fs.FileInfo, error) {
+				return nil, fs.ErrNotExist
+			})
 
 			if tc.fatal != "" {
 				t.Fatalf("copyPaths: expected fatal %q", tc.fatal)

internal/outcome/dispatcher_test.go

@@ -23,6 +23,7 @@ import (
 	"hakurei.app/container/seccomp"
 	"hakurei.app/container/std"
 	"hakurei.app/hst"
+	"hakurei.app/internal/env"
 	"hakurei.app/internal/stub"
 	"hakurei.app/internal/system"
 	"hakurei.app/message"
@@ -174,6 +175,7 @@ func checkOpBehaviour(t *testing.T, testCases []opBehaviourTestCase) {
 		call("cmdOutput", stub.ExpectArgs{container.Nonexistent, os.Stderr, []string{}, "/"}, []byte("0"), nil),
 		call("tempdir", stub.ExpectArgs{}, container.Nonexistent+"/tmp", nil),
 		call("lookupEnv", stub.ExpectArgs{"XDG_RUNTIME_DIR"}, wantRuntimePath, nil),
+		call("stat", stub.ExpectArgs{env.VarRunNscd}, stubFileInfoIsDir(true), nil),
 		call("getuid", stub.ExpectArgs{}, 1000, nil),
 		call("getgid", stub.ExpectArgs{}, 100, nil),
 

internal/outcome/outcome.go

@@ -110,7 +110,7 @@ func newOutcomeState(k syscallDispatcher, msg message.Msg, id *hst.ID, config *h
 		Paths: env.CopyPathsFunc(k.fatalf, k.tempdir, func(key string) string {
 			v, _ := k.lookupEnv(key)
 			return v
-		}),
+		}, k.stat),
 		Container: config.Container,
 	}
 

internal/outcome/run_test.go

@@ -710,7 +710,7 @@ func (k *stubNixOS) lookupEnv(key string) (string, bool) {
 func (k *stubNixOS) stat(name string) (fs.FileInfo, error) {
 	switch name {
 	case "/var/run/nscd":
-		return nil, nil
+		return stubFileInfoIsDir(true), nil
 	case "/run/user/1971/pulse":
 		return nil, nil
 	case "/run/user/1971/pulse/native":

internal/outcome/spcontainer.go

@@ -18,13 +18,12 @@ import (
 	"hakurei.app/hst"
 	"hakurei.app/internal/acl"
 	"hakurei.app/internal/dbus"
+	"hakurei.app/internal/env"
 	"hakurei.app/internal/system"
 	"hakurei.app/internal/validate"
 	"hakurei.app/message"
 )
 
-const varRunNscd = fhs.Var + "run/nscd"
-
 func init() { gob.Register(new(spParamsOp)) }
 
 // spParamsOp initialises unordered fields of [container.Params] and the
@@ -136,17 +135,23 @@ type spFilesystemOp struct {
 }
 
 func (s *spFilesystemOp) toSystem(state *outcomeStateSys) error {
-	/* retrieve paths and hide them if they're made available in the sandbox;
-
-	this feature tries to improve user experience of permissive defaults, and
-	to warn about issues in custom configuration; it is NOT a security feature
-	and should not be treated as such, ALWAYS be careful with what you bind */
+	// retrieve paths and hide them if they're made available in the sandbox
+	//
+	// this feature tries to improve user experience of permissive defaults, and
+	// to warn about issues in custom configuration; it is NOT a security feature
+	// and should not be treated as such, ALWAYS be careful with what you bind
 	hidePaths := []string{
 		state.sc.RuntimePath.String(),
 		state.sc.SharePath.String(),
+	}
 
-		// this causes emulated passwd database to be bypassed on some /etc/ setups
-		varRunNscd,
+	if state.Paths == nil || state.HasNscd {
+		hidePaths = append(hidePaths,
+			// this causes emulated passwd database to be bypassed on some /etc/
+			// setups, made optional to avoid needlessly creating it on
+			// non-glibc systems when invoking permissive defaults
+			env.VarRunNscd,
+		)
 	}
 
 	// dbus.Address does not go through syscallDispatcher