Resolve users and groups through NSS in a shared getent package

client/internal/elevate/trusted_unix.go

@@ -3,23 +3,18 @@
 package elevate
 
 import (
-	"bufio"
 	"errors"
 	"fmt"
 	"os"
-	"os/user"
 	"path/filepath"
 	"slices"
 	"strconv"
-	"strings"
 	"syscall"
 
 	log "github.com/sirupsen/logrus"
-)
 
-// groupFile lists which accounts are in which group, for the membership a user
+	"github.com/netbirdio/netbird/client/internal/getent"
-// private group's name does not state: see groupHasOtherMembers.
+)
-const groupFile = "/etc/group"
 
 // checkOnlyOwnerWritable reports an error unless path, and every directory leading
 // to it, is owned by either root or this user and writable by nobody who could not
@@ -89,12 +84,12 @@ func groupWriteAllowed(uid, gid uint32) bool {
 		return true
 	}
 
-	group, err := user.LookupGroupId(strconv.FormatUint(uint64(gid), 10))
+	group, err := getent.LookupGroupID(strconv.FormatUint(uint64(gid), 10))
 	if err != nil {
 		log.Debugf("cannot look up group %d, treating it as shared: %v", gid, err)
 		return false
 	}
-	owner, err := user.LookupId(strconv.FormatUint(uint64(uid), 10))
+	owner, err := getent.LookupUserID(strconv.FormatUint(uint64(uid), 10))
 	if err != nil {
 		log.Debugf("cannot look up uid %d, treating its group as shared: %v", uid, err)
 		return false
@@ -103,7 +98,7 @@ func groupWriteAllowed(uid, gid uint32) bool {
 	if group.Name != owner.Username {
 		return false
 	}
-	return !groupHasOtherMembers(groupFile, group.Name, owner.Username)
+	return !groupHasOtherMembers(group.Name, owner.Username)
 }
 
 // groupHasOtherMembers reports whether the group lists a member besides owner.
@@ -111,36 +106,14 @@ func groupWriteAllowed(uid, gid uint32) bool {
 // Sharing the owner's name is what a user private group is recognised by, and it
 // says nothing about who is in it: a group that has since gained a member is
 // still named that way, and that member can write whatever the group can. So the
-// membership is read rather than assumed. A group this file does not describe,
+// membership is read rather than assumed. A group whose members cannot be
-// because it comes from LDAP or another NSS source, cannot be answered here and
+// listed, because no source on this host describes it, leaves the name as the
-// leaves the name as the only thing to go on.
+// only thing to go on.
-func groupHasOtherMembers(path, name, owner string) bool {
+func groupHasOtherMembers(name, owner string) bool {
-	file, err := os.Open(path)
+	members, err := getent.GroupMembers(name)
 	if err != nil {
-		log.Debugf("cannot read %s for the members of group %q: %v", path, name, err)
+		log.Debugf("cannot list the members of group %q, going by its name alone: %v", name, err)
 		return false
 	}
-	defer func() {
+	return slices.ContainsFunc(members, func(member string) bool { return member != owner })
-		if err := file.Close(); err != nil {
-			log.Debugf("close %s: %v", path, err)
-		}
-	}()
-
-	scanner := bufio.NewScanner(file)
-	for scanner.Scan() {
-		// name:password:gid:member,member
-		fields := strings.Split(scanner.Text(), ":")
-		if len(fields) < 4 || fields[0] != name {
-			continue
-		}
-		for member := range strings.SplitSeq(fields[3], ",") {
-			if member != "" && member != owner {
-				return true
-			}
-		}
-	}
-	if err := scanner.Err(); err != nil {
-		log.Debugf("read %s: %v", path, err)
-	}
-	return false
 }

client/internal/elevate/trusted_unix_test.go

@@ -93,41 +93,13 @@ func TestCheckOnlyOwnerWritableAcceptsOwnPrivateGroup(t *testing.T) {
 	assert.NoError(t, err, "group write in the owner's own private group reaches nobody else")
 }
 
-// A group that shares its owner's name but has gained another member is no longer
+// A group whose membership no source can answer for leaves the name as the only
-// private, and its write access reaches an account that could not elevate.
+// thing to go on, so the private-group allowance stands rather than collapsing on
-func TestGroupHasOtherMembers(t *testing.T) {
+// every host whose groups come from an unreadable source. The membership listing
-	tests := []struct {
+// itself lives in the getent package and is tested there.
-		name  string
-		entry string
-		want  bool
-	}{
-		{name: "no members", entry: "vma:x:1000:"},
-		{name: "only the owner", entry: "vma:x:1000:vma"},
-		{name: "another member", entry: "vma:x:1000:bob", want: true},
-		{name: "the owner and another", entry: "vma:x:1000:vma,bob", want: true},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			path := filepath.Join(t.TempDir(), "group")
-			body := "root:x:0:\n" + tt.entry + "\nsudo:x:27:vma\n"
-			require.NoError(t, os.WriteFile(path, []byte(body), 0o644), "write the group file")
-
-			assert.Equal(t, tt.want, groupHasOtherMembers(path, "vma", "vma"), "entry %q", tt.entry)
-		})
-	}
-}
-
-// A group file that says nothing about the group leaves the name as the only thing
-// to go on, so the private-group allowance stands rather than collapsing on every
-// host whose groups come from LDAP.
 func TestGroupHasOtherMembersTolerantOfAnUnknownGroup(t *testing.T) {
-	path := filepath.Join(t.TempDir(), "group")
+	assert.False(t, groupHasOtherMembers("nonexistent_group_xyzzy_12345", "vma"),
-	require.NoError(t, os.WriteFile(path, []byte("root:x:0:\n"), 0o644), "write the group file")
+		"a group no source describes")
-
-	assert.False(t, groupHasOtherMembers(path, "vma", "vma"), "a group the file does not describe")
-	assert.False(t, groupHasOtherMembers(filepath.Join(t.TempDir(), "absent"), "vma", "vma"),
-		"no group file at all")
 }
 
 // A writable directory is as good as a writable file: whoever can write the
@@ -171,7 +143,7 @@ func requirePrivatePrimaryGroup(t *testing.T) {
 	if group.Name != self.Username {
 		t.Skipf("the test user's primary group is %q, not their own, so there is nothing to assert here", group.Name)
 	}
-	if groupHasOtherMembers(groupFile, group.Name, self.Username) {
+	if groupHasOtherMembers(group.Name, self.Username) {
 		t.Skipf("group %q has other members, so it is not a private group", group.Name)
 	}
 }

client/internal/getent/cgo_unix.go

@@ -0,0 +1,36 @@
+//go:build cgo && !osusergo && !windows
+
+package getent
+
+import "os/user"
+
+// Built with cgo, os/user resolves through libc (getpwnam_r and friends),
+// which goes through the host's NSS stack natively. Whatever it fails to
+// find, the getent command would not find either, so there is nothing to
+// fall back to.
+
+// LookupUser looks up a user by name.
+func LookupUser(username string) (*user.User, error) {
+	return user.Lookup(username)
+}
+
+// LookupUserID looks up a user by UID.
+func LookupUserID(uid string) (*user.User, error) {
+	return user.LookupId(uid)
+}
+
+// CurrentUser returns the user this process runs as.
+func CurrentUser() (*user.User, error) {
+	return user.Current()
+}
+
+// LookupGroupID looks up a group by GID.
+func LookupGroupID(gid string) (*user.Group, error) {
+	return user.LookupGroupId(gid)
+}
+
+// GroupIDs returns the IDs of the groups the user is a member of; libc's
+// getgrouplist handles NSS groups natively.
+func GroupIDs(u *user.User) ([]string, error) {
+	return u.GroupIds()
+}

client/internal/getent/getent.go

@@ -0,0 +1,6 @@
+// Package getent resolves users and groups through the host's NSS stack.
+// Built without cgo, os/user reads /etc/passwd and /etc/group alone and misses
+// anything LDAP, SSSD or winbind provide; the getent and id commands resolve
+// through NSS whatever the build. The lookups here try the standard library
+// first, which needs no subprocess, and fall back to those commands.
+package getent

client/internal/getent/getent_test.go

@@ -1,4 +1,4 @@
-package server
+package getent
 
 import (
 	"os/user"
@@ -10,38 +10,48 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestLookupWithGetent_CurrentUser(t *testing.T) {
+func TestLookupUser_CurrentUser(t *testing.T) {
 	// The current user should always be resolvable on any platform
 	current, err := user.Current()
 	require.NoError(t, err)
 
-	u, err := lookupWithGetent(current.Username)
+	u, err := LookupUser(current.Username)
 	require.NoError(t, err)
 	assert.Equal(t, current.Username, u.Username)
 	assert.Equal(t, current.Uid, u.Uid)
 	assert.Equal(t, current.Gid, u.Gid)
 }
 
-func TestLookupWithGetent_NonexistentUser(t *testing.T) {
+func TestLookupUser_NonexistentUser(t *testing.T) {
-	_, err := lookupWithGetent("nonexistent_user_xyzzy_12345")
+	_, err := LookupUser("nonexistent_user_xyzzy_12345")
 	require.Error(t, err, "should fail for nonexistent user")
 }
 
-func TestCurrentUserWithGetent(t *testing.T) {
+func TestLookupUserID_CurrentUser(t *testing.T) {
+	current, err := user.Current()
+	require.NoError(t, err)
+
+	u, err := LookupUserID(current.Uid)
+	require.NoError(t, err)
+	assert.Equal(t, current.Username, u.Username)
+	assert.Equal(t, current.Uid, u.Uid)
+}
+
+func TestCurrentUser(t *testing.T) {
 	stdUser, err := user.Current()
 	require.NoError(t, err)
 
-	u, err := currentUserWithGetent()
+	u, err := CurrentUser()
 	require.NoError(t, err)
 	assert.Equal(t, stdUser.Uid, u.Uid)
 	assert.Equal(t, stdUser.Username, u.Username)
 }
 
-func TestGroupIdsWithFallback_CurrentUser(t *testing.T) {
+func TestGroupIDs_CurrentUser(t *testing.T) {
 	current, err := user.Current()
 	require.NoError(t, err)
 
-	groups, err := groupIdsWithFallback(current)
+	groups, err := GroupIDs(current)
 	require.NoError(t, err)
 	require.NotEmpty(t, groups, "current user should have at least one group")
 
@@ -53,32 +63,30 @@ func TestGroupIdsWithFallback_CurrentUser(t *testing.T) {
 	}
 }
 
-func TestGetShellFromGetent_CurrentUser(t *testing.T) {
+func TestUserShell_CurrentUser(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		// Windows stub always returns empty, which is correct
-		shell := getShellFromGetent("1000")
-		assert.Empty(t, shell, "Windows stub should return empty")
-		return
-	}
-
 	current, err := user.Current()
 	require.NoError(t, err)
 
-	// getent may not be available on all systems (e.g., macOS without Homebrew getent)
+	// getent may not be available on all systems (e.g., macOS without
-	shell := getShellFromGetent(current.Uid)
+	// Homebrew getent), and Windows has no login shells at all.
+	shell, err := UserShell(current.Uid)
+	if err != nil {
+		t.Logf("UserShell failed, getent may not be available: %v", err)
+		return
+	}
 	if shell == "" {
-		t.Log("getShellFromGetent returned empty, getent may not be available")
+		t.Log("UserShell returned empty, the user has no shell set")
 		return
 	}
 	assert.True(t, shell[0] == '/', "shell should be an absolute path, got %q", shell)
 }
 
-func TestLookupWithGetent_RootUser(t *testing.T) {
+func TestLookupUser_RootUser(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("no root user on Windows")
 	}
 
-	u, err := lookupWithGetent("root")
+	u, err := LookupUser("root")
 	if err != nil {
 		t.Skip("root user not available on this system")
 	}
@@ -86,25 +94,25 @@ func TestLookupWithGetent_RootUser(t *testing.T) {
 }
 
 // TestIntegration_FullLookupChain exercises the complete user lookup chain
-// against the real system, testing that all wrappers (lookupWithGetent,
+// against the real system, testing that all wrappers (LookupUser,
-// currentUserWithGetent, groupIdsWithFallback, getShellFromGetent) produce
+// CurrentUser, GroupIDs, UserShell) produce consistent and correct results
-// consistent and correct results when composed together.
+// when composed together.
 func TestIntegration_FullLookupChain(t *testing.T) {
-	// Step 1: currentUserWithGetent must resolve the running user.
+	// Step 1: CurrentUser must resolve the running user.
-	current, err := currentUserWithGetent()
+	current, err := CurrentUser()
-	require.NoError(t, err, "currentUserWithGetent must resolve the running user")
+	require.NoError(t, err, "CurrentUser must resolve the running user")
 	require.NotEmpty(t, current.Uid)
 	require.NotEmpty(t, current.Username)
 
-	// Step 2: lookupWithGetent by the same username must return matching identity.
+	// Step 2: LookupUser by the same username must return matching identity.
-	byName, err := lookupWithGetent(current.Username)
+	byName, err := LookupUser(current.Username)
 	require.NoError(t, err)
 	assert.Equal(t, current.Uid, byName.Uid, "lookup by name should return same UID")
 	assert.Equal(t, current.Gid, byName.Gid, "lookup by name should return same GID")
 	assert.Equal(t, current.HomeDir, byName.HomeDir, "lookup by name should return same home")
 
-	// Step 3: groupIdsWithFallback must return at least the primary GID.
+	// Step 3: GroupIDs must return at least the primary GID.
-	groups, err := groupIdsWithFallback(current)
+	groups, err := GroupIDs(current)
 	require.NoError(t, err)
 	require.NotEmpty(t, groups, "user must have at least one group")
 
@@ -119,29 +127,20 @@ func TestIntegration_FullLookupChain(t *testing.T) {
 		}
 	}
 	assert.True(t, foundPrimary, "primary GID %s should appear in supplementary groups", current.Gid)
-
-	// Step 4: getShellFromGetent should either return a valid shell path or empty
-	// (empty is OK when getent is not available, e.g. macOS without Homebrew getent).
-	if runtime.GOOS != "windows" {
-		shell := getShellFromGetent(current.Uid)
-		if shell != "" {
-			assert.True(t, shell[0] == '/', "shell should be an absolute path, got %q", shell)
-		}
-	}
 }
 
 // TestIntegration_LookupAndGroupsConsistency verifies that a user resolved via
-// lookupWithGetent can have their groups resolved via groupIdsWithFallback,
+// LookupUser can have their groups resolved via GroupIDs, testing the handoff
-// testing the handoff between the two functions as used by the SSH server.
+// between the two functions as used by the SSH server.
 func TestIntegration_LookupAndGroupsConsistency(t *testing.T) {
 	current, err := user.Current()
 	require.NoError(t, err)
 
 	// Simulate the SSH server flow: lookup user, then get their groups.
-	resolved, err := lookupWithGetent(current.Username)
+	resolved, err := LookupUser(current.Username)
 	require.NoError(t, err)
 
-	groups, err := groupIdsWithFallback(resolved)
+	groups, err := GroupIDs(resolved)
 	require.NoError(t, err)
 	require.NotEmpty(t, groups, "resolved user must have groups")
 
@@ -154,19 +153,3 @@ func TestIntegration_LookupAndGroupsConsistency(t *testing.T) {
 		}
 	}
 }
-
-// TestIntegration_ShellLookupChain tests the full shell resolution chain
-// (getShellFromPasswd -> getShellFromGetent -> $SHELL -> default) on Unix.
-func TestIntegration_ShellLookupChain(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Unix shell lookup not applicable on Windows")
-	}
-
-	current, err := user.Current()
-	require.NoError(t, err)
-
-	// getUserShell is the top-level function used by the SSH server.
-	shell := getUserShell(current.Uid)
-	require.NotEmpty(t, shell, "getUserShell must always return a shell")
-	assert.True(t, shell[0] == '/', "shell should be an absolute path, got %q", shell)
-}

client/internal/getent/nocgo_unix.go

@@ -0,0 +1,110 @@
+//go:build (!cgo || osusergo) && !windows
+
+package getent
+
+import (
+	"os"
+	"os/user"
+	"strconv"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// Without cgo, os/user only reads /etc/passwd and /etc/group and misses
+// NSS-provided users and groups; the getent and id commands go through the
+// host's NSS stack.
+
+// LookupUser looks up a user by name, falling back to getent if os/user fails.
+func LookupUser(username string) (*user.User, error) {
+	u, err := user.Lookup(username)
+	if err == nil {
+		return u, nil
+	}
+
+	stdErr := err
+	log.Debugf("os/user.Lookup(%q) failed, trying getent: %v", username, err)
+
+	u, _, getentErr := passwdLookup(username)
+	if getentErr != nil {
+		log.Debugf("getent fallback for %q also failed: %v", username, getentErr)
+		return nil, stdErr
+	}
+	return u, nil
+}
+
+// LookupUserID looks up a user by UID, falling back to getent if os/user fails.
+func LookupUserID(uid string) (*user.User, error) {
+	u, err := user.LookupId(uid)
+	if err == nil {
+		return u, nil
+	}
+
+	stdErr := err
+	log.Debugf("os/user.LookupId(%q) failed, trying getent: %v", uid, err)
+
+	u, _, getentErr := passwdLookup(uid)
+	if getentErr != nil {
+		log.Debugf("getent fallback for uid %s also failed: %v", uid, getentErr)
+		return nil, stdErr
+	}
+	return u, nil
+}
+
+// CurrentUser returns the user this process runs as, falling back to getent
+// if os/user fails.
+func CurrentUser() (*user.User, error) {
+	u, err := user.Current()
+	if err == nil {
+		return u, nil
+	}
+
+	stdErr := err
+	uid := strconv.Itoa(os.Getuid())
+	log.Debugf("os/user.Current() failed, trying getent with UID %s: %v", uid, err)
+
+	u, _, getentErr := passwdLookup(uid)
+	if getentErr != nil {
+		return nil, stdErr
+	}
+	return u, nil
+}
+
+// LookupGroupID looks up a group by GID, falling back to getent if os/user
+// fails.
+func LookupGroupID(gid string) (*user.Group, error) {
+	g, err := user.LookupGroupId(gid)
+	if err == nil {
+		return g, nil
+	}
+
+	stdErr := err
+	log.Debugf("os/user.LookupGroupId(%q) failed, trying getent: %v", gid, err)
+
+	g, _, getentErr := groupLookup(gid)
+	if getentErr != nil {
+		log.Debugf("getent fallback for gid %s also failed: %v", gid, getentErr)
+		return nil, stdErr
+	}
+	return g, nil
+}
+
+// GroupIDs returns the IDs of the groups the user is a member of.
+// NOTE: unlike the lookups above, which try the standard library first, this
+// intentionally tries `id -G` first because without cgo, user.GroupIds only
+// reads /etc/group and silently returns incomplete results for NSS users
+// (no error, just missing groups). The id command goes through NSS and
+// returns the full set.
+func GroupIDs(u *user.User) ([]string, error) {
+	ids, err := idGroups(u.Username)
+	if err == nil {
+		return ids, nil
+	}
+
+	log.Debugf("id -G %q failed, falling back to user.GroupIds(): %v", u.Username, err)
+
+	ids, stdErr := u.GroupIds()
+	if stdErr != nil {
+		return nil, stdErr
+	}
+	return ids, nil
+}

client/internal/getent/unix.go

@@ -0,0 +1,224 @@
+//go:build !windows
+
+package getent
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"os/user"
+	"runtime"
+	"strings"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const commandTimeout = 5 * time.Second
+
+// groupFile lists which accounts are in which group, for hosts where the
+// getent command is not available (macOS ships without it).
+const groupFile = "/etc/group"
+
+// UserShell returns the login shell getent reports for the user with this UID.
+// It reaches shells that /etc/passwd does not list, because getent resolves
+// through the host's NSS stack.
+func UserShell(uid string) (string, error) {
+	_, shell, err := passwdLookup(uid)
+	if err != nil {
+		return "", err
+	}
+	return shell, nil
+}
+
+// GroupMembers returns the names of the group's members: from getent, which
+// resolves through NSS, or from /etc/group where getent is not available. A
+// group neither source describes is an error; an empty member list is not,
+// since accounts with the group as their primary one are not listed in it.
+func GroupMembers(name string) ([]string, error) {
+	_, members, err := groupLookup(name)
+	if err == nil {
+		return members, nil
+	}
+	log.Debugf("getent cannot list group %q, reading %s: %v", name, groupFile, err)
+	return groupMembersFromFile(groupFile, name)
+}
+
+// passwdLookup executes `getent passwd <query>`, where query is a username or
+// UID, and returns the user and login shell.
+func passwdLookup(query string) (*user.User, string, error) {
+	out, err := run("passwd", query)
+	if err != nil {
+		return nil, "", err
+	}
+	return parsePasswd(string(out))
+}
+
+// groupLookup executes `getent group <query>`, where query is a group name or
+// GID, and returns the group and its member names.
+func groupLookup(query string) (*user.Group, []string, error) {
+	out, err := run("group", query)
+	if err != nil {
+		return nil, nil, err
+	}
+	return parseGroup(string(out))
+}
+
+// run executes `getent <database> <key>` with a timeout.
+func run(database, key string) ([]byte, error) {
+	if !validateInput(key) {
+		return nil, fmt.Errorf("invalid getent input: %q", key)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), commandTimeout)
+	defer cancel()
+
+	out, err := exec.CommandContext(ctx, "getent", database, key).Output()
+	if err != nil {
+		return nil, fmt.Errorf("getent %s %s: %w", database, key, err)
+	}
+	return out, nil
+}
+
+// parsePasswd parses getent passwd output: "name:x:uid:gid:gecos:home:shell"
+func parsePasswd(output string) (*user.User, string, error) {
+	fields := strings.SplitN(strings.TrimSpace(output), ":", 8)
+	if len(fields) < 6 {
+		return nil, "", fmt.Errorf("unexpected getent output (need 6+ fields): %q", output)
+	}
+
+	if fields[0] == "" || fields[2] == "" || fields[3] == "" {
+		return nil, "", fmt.Errorf("missing required fields in getent output: %q", output)
+	}
+
+	var shell string
+	if len(fields) >= 7 {
+		shell = fields[6]
+	}
+
+	return &user.User{
+		Username: fields[0],
+		Uid:      fields[2],
+		Gid:      fields[3],
+		Name:     fields[4],
+		HomeDir:  fields[5],
+	}, shell, nil
+}
+
+// parseGroup parses getent group output: "name:x:gid:member,member"
+func parseGroup(output string) (*user.Group, []string, error) {
+	fields := strings.SplitN(strings.TrimSpace(output), ":", 4)
+	if len(fields) < 3 {
+		return nil, nil, fmt.Errorf("unexpected getent output (need 3+ fields): %q", output)
+	}
+
+	if fields[0] == "" || fields[2] == "" {
+		return nil, nil, fmt.Errorf("missing required fields in getent output: %q", output)
+	}
+
+	var members []string
+	if len(fields) >= 4 {
+		members = splitMembers(fields[3])
+	}
+	return &user.Group{Name: fields[0], Gid: fields[2]}, members, nil
+}
+
+func splitMembers(list string) []string {
+	var members []string
+	for member := range strings.SplitSeq(list, ",") {
+		if member != "" {
+			members = append(members, member)
+		}
+	}
+	return members
+}
+
+// groupMembersFromFile finds the group's member list in a file of /etc/group's
+// format. A group the file does not describe, because it comes from LDAP or
+// another NSS source, is an error rather than an empty list.
+func groupMembersFromFile(path, name string) ([]string, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("open %s: %w", path, err)
+	}
+	defer func() {
+		if err := file.Close(); err != nil {
+			log.Debugf("close %s: %v", path, err)
+		}
+	}()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		// name:password:gid:member,member
+		fields := strings.Split(scanner.Text(), ":")
+		if len(fields) < 4 || fields[0] != name {
+			continue
+		}
+		return splitMembers(fields[3]), nil
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("read %s: %w", path, err)
+	}
+	return nil, fmt.Errorf("%s does not describe group %q", path, name)
+}
+
+// validateInput checks that the input is safe to pass to getent or id.
+// Allows POSIX usernames, numeric IDs, and common NSS extensions
+// (@ for Kerberos, $ for Samba, + for NIS compat). A leading hyphen is
+// rejected so the input can never be parsed as a command-line flag.
+func validateInput(input string) bool {
+	maxLen := 32
+	if runtime.GOOS == "linux" {
+		maxLen = 256
+	}
+
+	if len(input) == 0 || len(input) > maxLen {
+		return false
+	}
+
+	if input[0] == '-' {
+		return false
+	}
+
+	for _, r := range input {
+		if isAllowedChar(r) {
+			continue
+		}
+		return false
+	}
+	return true
+}
+
+func isAllowedChar(r rune) bool {
+	if r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' {
+		return true
+	}
+	switch r {
+	case '.', '_', '-', '@', '+', '$':
+		return true
+	}
+	return false
+}
+
+// idGroups runs `id -G <username>` and returns the space-separated group IDs.
+func idGroups(username string) ([]string, error) {
+	if !validateInput(username) {
+		return nil, fmt.Errorf("invalid username for id command: %q", username)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), commandTimeout)
+	defer cancel()
+
+	out, err := exec.CommandContext(ctx, "id", "-G", username).Output()
+	if err != nil {
+		return nil, fmt.Errorf("id -G %s: %w", username, err)
+	}
+
+	trimmed := strings.TrimSpace(string(out))
+	if trimmed == "" {
+		return nil, fmt.Errorf("id -G %s: empty output", username)
+	}
+	return strings.Fields(trimmed), nil
+}

client/internal/getent/unix_test.go

@@ -1,10 +1,12 @@
 //go:build !windows
 
-package server
+package getent
 
 import (
+	"os"
 	"os/exec"
 	"os/user"
+	"path/filepath"
 	"runtime"
 	"strconv"
 	"testing"
@@ -13,7 +15,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestParseGetentPasswd(t *testing.T) {
+func TestParsePasswd(t *testing.T) {
 	tests := []struct {
 		name        string
 		input       string
@@ -128,7 +130,7 @@ func TestParseGetentPasswd(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			u, shell, err := parseGetentPasswd(tt.input)
+			u, shell, err := parsePasswd(tt.input)
 			if tt.wantErr {
 				require.Error(t, err)
 				if tt.errContains != "" {
@@ -147,7 +149,119 @@ func TestParseGetentPasswd(t *testing.T) {
 	}
 }
 
-func TestValidateGetentInput(t *testing.T) {
+func TestParseGroup(t *testing.T) {
+	tests := []struct {
+		name        string
+		input       string
+		wantGroup   *user.Group
+		wantMembers []string
+		wantErr     bool
+	}{
+		{
+			name:      "no members",
+			input:     "vma:x:1000:\n",
+			wantGroup: &user.Group{Name: "vma", Gid: "1000"},
+		},
+		{
+			name:        "one member",
+			input:       "sudo:x:27:alice",
+			wantGroup:   &user.Group{Name: "sudo", Gid: "27"},
+			wantMembers: []string{"alice"},
+		},
+		{
+			name:        "several members",
+			input:       "docker:x:998:alice,bob\n",
+			wantGroup:   &user.Group{Name: "docker", Gid: "998"},
+			wantMembers: []string{"alice", "bob"},
+		},
+		{
+			name:    "too few fields",
+			input:   "bad:x",
+			wantErr: true,
+		},
+		{
+			name:    "empty group name",
+			input:   ":x:1000:alice",
+			wantErr: true,
+		},
+		{
+			name:    "empty GID",
+			input:   "vma:x::alice",
+			wantErr: true,
+		},
+		{
+			name:    "empty input",
+			input:   "",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g, members, err := parseGroup(tt.input)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tt.wantGroup.Name, g.Name, "group name")
+			assert.Equal(t, tt.wantGroup.Gid, g.Gid, "GID")
+			assert.Equal(t, tt.wantMembers, members, "members")
+		})
+	}
+}
+
+func TestGroupMembersFromFile(t *testing.T) {
+	tests := []struct {
+		name  string
+		entry string
+		want  []string
+	}{
+		{name: "no members", entry: "vma:x:1000:"},
+		{name: "only the owner", entry: "vma:x:1000:vma", want: []string{"vma"}},
+		{name: "two members", entry: "vma:x:1000:vma,bob", want: []string{"vma", "bob"}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			path := filepath.Join(t.TempDir(), "group")
+			body := "root:x:0:\n" + tt.entry + "\nsudo:x:27:vma\n"
+			require.NoError(t, os.WriteFile(path, []byte(body), 0o644), "write the group file")
+
+			members, err := groupMembersFromFile(path, "vma")
+			require.NoError(t, err, "entry %q", tt.entry)
+			assert.Equal(t, tt.want, members, "entry %q", tt.entry)
+		})
+	}
+}
+
+// A group the file does not describe, because it comes from LDAP or another
+// NSS source, is an error rather than an empty member list: the caller must
+// be able to tell "no members" from "no answer".
+func TestGroupMembersFromFileUnknownGroup(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "group")
+	require.NoError(t, os.WriteFile(path, []byte("root:x:0:\n"), 0o644), "write the group file")
+
+	_, err := groupMembersFromFile(path, "vma")
+	assert.Error(t, err, "a group the file does not describe")
+
+	_, err = groupMembersFromFile(filepath.Join(t.TempDir(), "absent"), "vma")
+	assert.Error(t, err, "no group file at all")
+}
+
+// GroupMembers on the root group, which every Unix has, whichever source
+// answers for it.
+func TestGroupMembers_RootGroup(t *testing.T) {
+	rootGroup := "root"
+	if runtime.GOOS == "darwin" {
+		rootGroup = "wheel"
+	}
+
+	_, err := GroupMembers(rootGroup)
+	assert.NoError(t, err, "the %s group must be describable", rootGroup)
+}
+
+func TestValidateInput(t *testing.T) {
 	tests := []struct {
 		name  string
 		input string
@@ -180,7 +294,7 @@ func TestValidateGetentInput(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			assert.Equal(t, tt.want, validateGetentInput(tt.input))
+			assert.Equal(t, tt.want, validateInput(tt.input))
 		})
 	}
 }
@@ -193,12 +307,12 @@ func makeLongString(n int) string {
 	return string(b)
 }
 
-func TestRunGetent_RootUser(t *testing.T) {
+func TestPasswdLookup_RootUser(t *testing.T) {
 	if _, err := exec.LookPath("getent"); err != nil {
 		t.Skip("getent not available on this system")
 	}
 
-	u, shell, err := runGetent("root")
+	u, shell, err := passwdLookup("root")
 	require.NoError(t, err)
 	assert.Equal(t, "root", u.Username)
 	assert.Equal(t, "0", u.Uid)
@@ -206,44 +320,55 @@ func TestRunGetent_RootUser(t *testing.T) {
 	assert.NotEmpty(t, shell, "root should have a shell")
 }
 
-func TestRunGetent_ByUID(t *testing.T) {
+func TestPasswdLookup_ByUID(t *testing.T) {
 	if _, err := exec.LookPath("getent"); err != nil {
 		t.Skip("getent not available on this system")
 	}
 
-	u, _, err := runGetent("0")
+	u, _, err := passwdLookup("0")
 	require.NoError(t, err)
 	assert.Equal(t, "root", u.Username)
 	assert.Equal(t, "0", u.Uid)
 }
 
-func TestRunGetent_NonexistentUser(t *testing.T) {
+func TestPasswdLookup_NonexistentUser(t *testing.T) {
 	if _, err := exec.LookPath("getent"); err != nil {
 		t.Skip("getent not available on this system")
 	}
 
-	_, _, err := runGetent("nonexistent_user_xyzzy_12345")
+	_, _, err := passwdLookup("nonexistent_user_xyzzy_12345")
 	assert.Error(t, err)
 }
 
-func TestRunGetent_InvalidInput(t *testing.T) {
+func TestPasswdLookup_InvalidInput(t *testing.T) {
-	_, _, err := runGetent("")
+	_, _, err := passwdLookup("")
 	assert.Error(t, err)
 
-	_, _, err = runGetent("user\x00name")
+	_, _, err = passwdLookup("user\x00name")
 	assert.Error(t, err)
 }
 
-func TestRunGetent_NotAvailable(t *testing.T) {
+func TestPasswdLookup_NotAvailable(t *testing.T) {
 	if _, err := exec.LookPath("getent"); err == nil {
 		t.Skip("getent is available, can't test missing case")
 	}
 
-	_, _, err := runGetent("root")
+	_, _, err := passwdLookup("root")
 	assert.Error(t, err, "should fail when getent is not installed")
 }
 
-func TestRunIdGroups_CurrentUser(t *testing.T) {
+func TestGroupLookup_RootGroup(t *testing.T) {
+	if _, err := exec.LookPath("getent"); err != nil {
+		t.Skip("getent not available on this system")
+	}
+
+	g, _, err := groupLookup("0")
+	require.NoError(t, err)
+	assert.Equal(t, "0", g.Gid, "GID 0 resolves to the root group")
+	assert.NotEmpty(t, g.Name, "the root group has a name")
+}
+
+func TestIdGroups_CurrentUser(t *testing.T) {
 	if _, err := exec.LookPath("id"); err != nil {
 		t.Skip("id not available on this system")
 	}
@@ -251,7 +376,7 @@ func TestRunIdGroups_CurrentUser(t *testing.T) {
 	current, err := user.Current()
 	require.NoError(t, err)
 
-	groups, err := runIdGroups(current.Username)
+	groups, err := idGroups(current.Username)
 	require.NoError(t, err)
 	require.NotEmpty(t, groups, "current user should have at least one group")
 
@@ -261,20 +386,20 @@ func TestRunIdGroups_CurrentUser(t *testing.T) {
 	}
 }
 
-func TestRunIdGroups_NonexistentUser(t *testing.T) {
+func TestIdGroups_NonexistentUser(t *testing.T) {
 	if _, err := exec.LookPath("id"); err != nil {
 		t.Skip("id not available on this system")
 	}
 
-	_, err := runIdGroups("nonexistent_user_xyzzy_12345")
+	_, err := idGroups("nonexistent_user_xyzzy_12345")
 	assert.Error(t, err)
 }
 
-func TestRunIdGroups_InvalidInput(t *testing.T) {
+func TestIdGroups_InvalidInput(t *testing.T) {
-	_, err := runIdGroups("")
+	_, err := idGroups("")
 	assert.Error(t, err)
 
-	_, err = runIdGroups("user\x00name")
+	_, err = idGroups("user\x00name")
 	assert.Error(t, err)
 }
 
@@ -286,7 +411,7 @@ func TestGetentResultsMatchStdlib(t *testing.T) {
 	current, err := user.Current()
 	require.NoError(t, err)
 
-	getentUser, _, err := runGetent(current.Username)
+	getentUser, _, err := passwdLookup(current.Username)
 	require.NoError(t, err)
 
 	assert.Equal(t, current.Username, getentUser.Username, "username should match")
@@ -303,7 +428,7 @@ func TestGetentResultsMatchStdlib_ByUID(t *testing.T) {
 	current, err := user.Current()
 	require.NoError(t, err)
 
-	getentUser, _, err := runGetent(current.Uid)
+	getentUser, _, err := passwdLookup(current.Uid)
 	require.NoError(t, err)
 
 	assert.Equal(t, current.Username, getentUser.Username, "username should match when looked up by UID")
@@ -323,12 +448,12 @@ func TestIdGroupsMatchStdlib(t *testing.T) {
 		t.Skip("os/user.GroupIds() not working, likely CGO_ENABLED=0")
 	}
 
-	idGroups, err := runIdGroups(current.Username)
+	idGroupIDs, err := idGroups(current.Username)
 	require.NoError(t, err)
 
 	// Deduplicate both lists: id -G can return duplicates (e.g., root in Docker)
 	// and ElementsMatch treats duplicates as distinct.
-	assert.ElementsMatch(t, uniqueStrings(stdGroups), uniqueStrings(idGroups), "id -G should return same groups as os/user")
+	assert.ElementsMatch(t, uniqueStrings(stdGroups), uniqueStrings(idGroupIDs), "id -G should return same groups as os/user")
 }
 
 func uniqueStrings(ss []string) []string {
@@ -343,71 +468,3 @@ func uniqueStrings(ss []string) []string {
 	}
 	return out
 }
-
-// TestGetShellFromPasswd_CurrentUser verifies that getShellFromPasswd correctly
-// reads the current user's shell from /etc/passwd by comparing it against what
-// getent reports (which goes through NSS).
-func TestGetShellFromPasswd_CurrentUser(t *testing.T) {
-	current, err := user.Current()
-	require.NoError(t, err)
-
-	shell := getShellFromPasswd(current.Uid)
-	if shell == "" {
-		t.Skip("current user not found in /etc/passwd (may be an NSS-only user)")
-	}
-
-	assert.True(t, shell[0] == '/', "shell should be an absolute path, got %q", shell)
-
-	if _, err := exec.LookPath("getent"); err == nil {
-		_, getentShell, getentErr := runGetent(current.Uid)
-		if getentErr == nil && getentShell != "" {
-			assert.Equal(t, getentShell, shell, "shell from /etc/passwd should match getent")
-		}
-	}
-}
-
-// TestGetShellFromPasswd_RootUser verifies that getShellFromPasswd can read
-// root's shell from /etc/passwd. Root is guaranteed to be in /etc/passwd on
-// any standard Unix system.
-func TestGetShellFromPasswd_RootUser(t *testing.T) {
-	shell := getShellFromPasswd("0")
-	require.NotEmpty(t, shell, "root (UID 0) must be in /etc/passwd")
-	assert.True(t, shell[0] == '/', "root shell should be an absolute path, got %q", shell)
-}
-
-// TestGetShellFromPasswd_NonexistentUID verifies that getShellFromPasswd
-// returns empty for a UID that doesn't exist in /etc/passwd.
-func TestGetShellFromPasswd_NonexistentUID(t *testing.T) {
-	shell := getShellFromPasswd("4294967294")
-	assert.Empty(t, shell, "nonexistent UID should return empty shell")
-}
-
-// TestGetShellFromPasswd_MatchesGetentForKnownUsers reads /etc/passwd directly
-// and cross-validates every entry against getent to ensure parseGetentPasswd
-// and getShellFromPasswd agree on shell values.
-func TestGetShellFromPasswd_MatchesGetentForKnownUsers(t *testing.T) {
-	if _, err := exec.LookPath("getent"); err != nil {
-		t.Skip("getent not available")
-	}
-
-	// Pick a few well-known system UIDs that are virtually always in /etc/passwd.
-	uids := []string{"0"} // root
-
-	current, err := user.Current()
-	require.NoError(t, err)
-	uids = append(uids, current.Uid)
-
-	for _, uid := range uids {
-		passwdShell := getShellFromPasswd(uid)
-		if passwdShell == "" {
-			continue
-		}
-
-		_, getentShell, err := runGetent(uid)
-		if err != nil {
-			continue
-		}
-
-		assert.Equal(t, getentShell, passwdShell, "shell mismatch for UID %s", uid)
-	}
-}

client/internal/getent/windows.go

@@ -0,0 +1,36 @@
+//go:build windows
+
+package getent
+
+import (
+	"errors"
+	"os/user"
+)
+
+// Windows does not use NSS or getent; os/user resolves accounts there
+// without cgo, so everything delegates to it.
+
+// LookupUser looks up a user by name.
+func LookupUser(username string) (*user.User, error) {
+	return user.Lookup(username)
+}
+
+// LookupUserID looks up a user by UID.
+func LookupUserID(uid string) (*user.User, error) {
+	return user.LookupId(uid)
+}
+
+// CurrentUser returns the user this process runs as.
+func CurrentUser() (*user.User, error) {
+	return user.Current()
+}
+
+// GroupIDs returns the IDs of the groups the user is a member of.
+func GroupIDs(u *user.User) ([]string, error) {
+	return u.GroupIds()
+}
+
+// UserShell is unanswerable on Windows, which has no login-shell database.
+func UserShell(string) (string, error) {
+	return "", errors.ErrUnsupported
+}

client/ssh/server/getent_cgo_unix.go

@@ -1,24 +0,0 @@
-//go:build cgo && !osusergo && !windows
-
-package server
-
-import "os/user"
-
-// lookupWithGetent with CGO delegates directly to os/user.Lookup.
-// When CGO is enabled, os/user uses libc (getpwnam_r) which goes through
-// the NSS stack natively. If it fails, the user truly doesn't exist and
-// getent would also fail.
-func lookupWithGetent(username string) (*user.User, error) {
-	return user.Lookup(username)
-}
-
-// currentUserWithGetent with CGO delegates directly to os/user.Current.
-func currentUserWithGetent() (*user.User, error) {
-	return user.Current()
-}
-
-// groupIdsWithFallback with CGO delegates directly to user.GroupIds.
-// libc's getgrouplist handles NSS groups natively.
-func groupIdsWithFallback(u *user.User) ([]string, error) {
-	return u.GroupIds()
-}

client/ssh/server/getent_nocgo_unix.go

@@ -1,74 +0,0 @@
-//go:build (!cgo || osusergo) && !windows
-
-package server
-
-import (
-	"os"
-	"os/user"
-	"strconv"
-
-	log "github.com/sirupsen/logrus"
-)
-
-// lookupWithGetent looks up a user by name, falling back to getent if os/user fails.
-// Without CGO, os/user only reads /etc/passwd and misses NSS-provided users.
-// getent goes through the host's NSS stack.
-func lookupWithGetent(username string) (*user.User, error) {
-	u, err := user.Lookup(username)
-	if err == nil {
-		return u, nil
-	}
-
-	stdErr := err
-	log.Debugf("os/user.Lookup(%q) failed, trying getent: %v", username, err)
-
-	u, _, getentErr := runGetent(username)
-	if getentErr != nil {
-		log.Debugf("getent fallback for %q also failed: %v", username, getentErr)
-		return nil, stdErr
-	}
-
-	return u, nil
-}
-
-// currentUserWithGetent gets the current user, falling back to getent if os/user fails.
-func currentUserWithGetent() (*user.User, error) {
-	u, err := user.Current()
-	if err == nil {
-		return u, nil
-	}
-
-	stdErr := err
-	uid := strconv.Itoa(os.Getuid())
-	log.Debugf("os/user.Current() failed, trying getent with UID %s: %v", uid, err)
-
-	u, _, getentErr := runGetent(uid)
-	if getentErr != nil {
-		return nil, stdErr
-	}
-
-	return u, nil
-}
-
-// groupIdsWithFallback gets group IDs for a user via the id command first,
-// falling back to user.GroupIds().
-// NOTE: unlike lookupWithGetent/currentUserWithGetent which try stdlib first,
-// this intentionally tries `id -G` first because without CGO, user.GroupIds()
-// only reads /etc/group and silently returns incomplete results for NSS users
-// (no error, just missing groups). The id command goes through NSS and returns
-// the full set.
-func groupIdsWithFallback(u *user.User) ([]string, error) {
-	ids, err := runIdGroups(u.Username)
-	if err == nil {
-		return ids, nil
-	}
-
-	log.Debugf("id -G %q failed, falling back to user.GroupIds(): %v", u.Username, err)
-
-	ids, stdErr := u.GroupIds()
-	if stdErr != nil {
-		return nil, stdErr
-	}
-
-	return ids, nil
-}

client/ssh/server/getent_unix.go

@@ -1,127 +0,0 @@
-//go:build !windows
-
-package server
-
-import (
-	"context"
-	"fmt"
-	"os/exec"
-	"os/user"
-	"runtime"
-	"strings"
-	"time"
-)
-
-const getentTimeout = 5 * time.Second
-
-// getShellFromGetent gets a user's login shell via getent by UID.
-// This is needed even with CGO because getShellFromPasswd reads /etc/passwd
-// directly and won't find NSS-provided users there.
-func getShellFromGetent(userID string) string {
-	_, shell, err := runGetent(userID)
-	if err != nil {
-		return ""
-	}
-	return shell
-}
-
-// runGetent executes `getent passwd <query>` and returns the user and login shell.
-func runGetent(query string) (*user.User, string, error) {
-	if !validateGetentInput(query) {
-		return nil, "", fmt.Errorf("invalid getent input: %q", query)
-	}
-
-	ctx, cancel := context.WithTimeout(context.Background(), getentTimeout)
-	defer cancel()
-
-	out, err := exec.CommandContext(ctx, "getent", "passwd", query).Output()
-	if err != nil {
-		return nil, "", fmt.Errorf("getent passwd %s: %w", query, err)
-	}
-
-	return parseGetentPasswd(string(out))
-}
-
-// parseGetentPasswd parses getent passwd output: "name:x:uid:gid:gecos:home:shell"
-func parseGetentPasswd(output string) (*user.User, string, error) {
-	fields := strings.SplitN(strings.TrimSpace(output), ":", 8)
-	if len(fields) < 6 {
-		return nil, "", fmt.Errorf("unexpected getent output (need 6+ fields): %q", output)
-	}
-
-	if fields[0] == "" || fields[2] == "" || fields[3] == "" {
-		return nil, "", fmt.Errorf("missing required fields in getent output: %q", output)
-	}
-
-	var shell string
-	if len(fields) >= 7 {
-		shell = fields[6]
-	}
-
-	return &user.User{
-		Username: fields[0],
-		Uid:      fields[2],
-		Gid:      fields[3],
-		Name:     fields[4],
-		HomeDir:  fields[5],
-	}, shell, nil
-}
-
-// validateGetentInput checks that the input is safe to pass to getent or id.
-// Allows POSIX usernames, numeric UIDs, and common NSS extensions
-// (@ for Kerberos, $ for Samba, + for NIS compat). A leading hyphen is
-// rejected so the input can never be parsed as a command-line flag.
-func validateGetentInput(input string) bool {
-	maxLen := 32
-	if runtime.GOOS == "linux" {
-		maxLen = 256
-	}
-
-	if len(input) == 0 || len(input) > maxLen {
-		return false
-	}
-
-	if input[0] == '-' {
-		return false
-	}
-
-	for _, r := range input {
-		if isAllowedGetentChar(r) {
-			continue
-		}
-		return false
-	}
-	return true
-}
-
-func isAllowedGetentChar(r rune) bool {
-	if r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' {
-		return true
-	}
-	switch r {
-	case '.', '_', '-', '@', '+', '$':
-		return true
-	}
-	return false
-}
-
-// runIdGroups runs `id -G <username>` and returns the space-separated group IDs.
-func runIdGroups(username string) ([]string, error) {
-	if !validateGetentInput(username) {
-		return nil, fmt.Errorf("invalid username for id command: %q", username)
-	}
-
-	ctx, cancel := context.WithTimeout(context.Background(), getentTimeout)
-	defer cancel()
-
-	out, err := exec.CommandContext(ctx, "id", "-G", username).Output()
-	if err != nil {
-		return nil, fmt.Errorf("id -G %s: %w", username, err)
-	}
-
-	trimmed := strings.TrimSpace(string(out))
-	if trimmed == "" {
-		return nil, fmt.Errorf("id -G %s: empty output", username)
-	}
-	return strings.Fields(trimmed), nil
-}

client/ssh/server/getent_windows.go

@@ -1,26 +0,0 @@
-//go:build windows
-
-package server
-
-import "os/user"
-
-// lookupWithGetent on Windows just delegates to os/user.Lookup.
-// Windows does not use NSS/getent; its user lookup works without CGO.
-func lookupWithGetent(username string) (*user.User, error) {
-	return user.Lookup(username)
-}
-
-// currentUserWithGetent on Windows just delegates to os/user.Current.
-func currentUserWithGetent() (*user.User, error) {
-	return user.Current()
-}
-
-// getShellFromGetent is a no-op on Windows; shell resolution uses PowerShell detection.
-func getShellFromGetent(_ string) string {
-	return ""
-}
-
-// groupIdsWithFallback on Windows just delegates to u.GroupIds().
-func groupIdsWithFallback(u *user.User) ([]string, error) {
-	return u.GroupIds()
-}

client/ssh/server/shell.go

@@ -13,6 +13,8 @@ import (
 
 	"github.com/gliderlabs/ssh"
 	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/internal/getent"
 )
 
 const (
@@ -56,7 +58,11 @@ func getUnixUserShell(userID string) string {
 		return shell
 	}
 
-	if shell := getShellFromGetent(userID); shell != "" {
+	shell, err := getent.UserShell(userID)
+	if err != nil {
+		log.Debugf("look up the shell for uid %s through getent: %v", userID, err)
+	}
+	if shell != "" {
 		return shell
 	}
 

client/ssh/server/shell_unix_test.go

@@ -0,0 +1,94 @@
+//go:build !windows
+
+package server
+
+import (
+	"os/exec"
+	"os/user"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/netbirdio/netbird/client/internal/getent"
+)
+
+// TestGetShellFromPasswd_CurrentUser verifies that getShellFromPasswd correctly
+// reads the current user's shell from /etc/passwd by comparing it against what
+// getent reports (which goes through NSS).
+func TestGetShellFromPasswd_CurrentUser(t *testing.T) {
+	current, err := user.Current()
+	require.NoError(t, err)
+
+	shell := getShellFromPasswd(current.Uid)
+	if shell == "" {
+		t.Skip("current user not found in /etc/passwd (may be an NSS-only user)")
+	}
+
+	assert.True(t, shell[0] == '/', "shell should be an absolute path, got %q", shell)
+
+	if _, err := exec.LookPath("getent"); err == nil {
+		getentShell, getentErr := getent.UserShell(current.Uid)
+		if getentErr == nil && getentShell != "" {
+			assert.Equal(t, getentShell, shell, "shell from /etc/passwd should match getent")
+		}
+	}
+}
+
+// TestGetShellFromPasswd_RootUser verifies that getShellFromPasswd can read
+// root's shell from /etc/passwd. Root is guaranteed to be in /etc/passwd on
+// any standard Unix system.
+func TestGetShellFromPasswd_RootUser(t *testing.T) {
+	shell := getShellFromPasswd("0")
+	require.NotEmpty(t, shell, "root (UID 0) must be in /etc/passwd")
+	assert.True(t, shell[0] == '/', "root shell should be an absolute path, got %q", shell)
+}
+
+// TestGetShellFromPasswd_NonexistentUID verifies that getShellFromPasswd
+// returns empty for a UID that doesn't exist in /etc/passwd.
+func TestGetShellFromPasswd_NonexistentUID(t *testing.T) {
+	shell := getShellFromPasswd("4294967294")
+	assert.Empty(t, shell, "nonexistent UID should return empty shell")
+}
+
+// TestGetShellFromPasswd_MatchesGetentForKnownUsers reads /etc/passwd directly
+// and cross-validates every entry against getent to ensure the two shell
+// sources agree.
+func TestGetShellFromPasswd_MatchesGetentForKnownUsers(t *testing.T) {
+	if _, err := exec.LookPath("getent"); err != nil {
+		t.Skip("getent not available")
+	}
+
+	// Pick a few well-known system UIDs that are virtually always in /etc/passwd.
+	uids := []string{"0"} // root
+
+	current, err := user.Current()
+	require.NoError(t, err)
+	uids = append(uids, current.Uid)
+
+	for _, uid := range uids {
+		passwdShell := getShellFromPasswd(uid)
+		if passwdShell == "" {
+			continue
+		}
+
+		getentShell, err := getent.UserShell(uid)
+		if err != nil {
+			continue
+		}
+
+		assert.Equal(t, getentShell, passwdShell, "shell mismatch for UID %s", uid)
+	}
+}
+
+// TestIntegration_ShellLookupChain tests the full shell resolution chain
+// (getShellFromPasswd -> getent -> $SHELL -> default).
+func TestIntegration_ShellLookupChain(t *testing.T) {
+	current, err := user.Current()
+	require.NoError(t, err)
+
+	// getUserShell is the top-level function used by the SSH server.
+	shell := getUserShell(current.Uid)
+	require.NotEmpty(t, shell, "getUserShell must always return a shell")
+	assert.True(t, shell[0] == '/', "shell should be an absolute path, got %q", shell)
+}

client/ssh/server/user_utils.go

@@ -9,6 +9,8 @@ import (
 	"strings"
 
 	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/internal/getent"
 )
 
 var (
@@ -23,8 +25,8 @@ func isPlatformUnix() bool {
 
 // Dependency injection variables for testing - allows mocking dynamic runtime checks
 var (
-	getCurrentUser         = currentUserWithGetent
+	getCurrentUser         = getent.CurrentUser
-	lookupUser             = lookupWithGetent
+	lookupUser             = getent.LookupUser
 	getCurrentOS           = func() string { return runtime.GOOS }
 	getIsProcessPrivileged = isCurrentProcessPrivileged
 

client/ssh/server/userswitching_unix.go

@@ -16,6 +16,8 @@ import (
 
 	"github.com/gliderlabs/ssh"
 	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/internal/getent"
 )
 
 // POSIX portable filename character set regex: [a-zA-Z0-9._-]
@@ -160,7 +162,7 @@ func (s *Server) parseUserCredentials(localUser *user.User) (uint32, uint32, []u
 // getSupplementaryGroups retrieves supplementary group IDs for a user.
 // Uses id/getent fallback for NSS users in CGO_ENABLED=0 builds.
 func (s *Server) getSupplementaryGroups(u *user.User) ([]uint32, error) {
-	groupIDStrings, err := groupIdsWithFallback(u)
+	groupIDStrings, err := getent.GroupIDs(u)
 	if err != nil {
 		return nil, fmt.Errorf("get group IDs for user %s: %w", u.Username, err)
 	}