files/passwd: don't shell out to id

Use the user lookup logic we already have instead of shelling out to id
to see if users exist.

Fix up the existing logic to handle lookup errors and finding nothing
differently.

internal/distro/distro.go

@@ -33,9 +33,7 @@ var (
 	systemConfigDir = "/usr/lib/ignition"
 
 	// Helper programs
-	chrootCmd   = "chroot"
 	groupaddCmd = "groupadd"
-	idCmd       = "id"
 	mdadmCmd    = "mdadm"
 	mountCmd    = "mount"
 	sgdiskCmd   = "sgdisk"
@@ -71,9 +69,7 @@ func DiskByPartUUIDDir() string { return diskByPartUUIDDir }
 func KernelCmdlinePath() string { return kernelCmdlinePath }
 func SystemConfigDir() string   { return fromEnv("SYSTEM_CONFIG_DIR", systemConfigDir) }
 
-func ChrootCmd() string     { return chrootCmd }
 func GroupaddCmd() string   { return groupaddCmd }
-func IdCmd() string         { return idCmd }
 func MdadmCmd() string      { return mdadmCmd }
 func MountCmd() string      { return mountCmd }
 func SgdiskCmd() string     { return sgdiskCmd }

internal/exec/util/passwd.go

@@ -26,7 +26,6 @@ import (
 	"github.com/coreos/ignition/v2/config/v3_1_experimental/types"
 	"github.com/coreos/ignition/v2/internal/as_user"
 	"github.com/coreos/ignition/v2/internal/distro"
-	"github.com/coreos/ignition/v2/internal/log"
 )
 
 func appendIfTrue(args []string, test *bool, newargs string) []string {
@@ -111,18 +110,11 @@ func (u Util) EnsureUser(c types.PasswdUser) error {
 
 // CheckIfUserExists will return Info log when user is empty
 func (u Util) CheckIfUserExists(c types.PasswdUser) (bool, error) {
-	code := -1
-	cmd := exec.Command(distro.ChrootCmd(), u.DestDir, distro.IdCmd(), c.Name)
-	stdout, err := cmd.CombinedOutput()
+	_, err := u.userLookup(c.Name)
+	if _, ok := err.(user.UnknownUserError); ok {
+		return false, nil
+	}
 	if err != nil {
-		if exitErr, ok := err.(*exec.ExitError); ok {
-			code = exitErr.Sys().(syscall.WaitStatus).ExitStatus()
-		}
-		if code == 1 {
-			u.Info("checking if user \"%s\" exists: %s", c.Name, fmt.Errorf("[Attention] %v: Cmd: %s Stdout: %s", err, log.QuotedCmd(cmd), stdout))
-			return false, nil
-		}
-		u.Logger.Info("error encountered (%T): %v", err, err)
 		return false, err
 	}
 	return true, nil

internal/exec/util/user_group_lookup.c

@@ -62,10 +62,16 @@ static int user_lookup_fn(lookup_ctxt_t *ctxt) {
 		goto out_err;
 	}
 
-	if(getpwnam_r(ctxt->name, &p, buf, sizeof(buf), &pptr) != 0 || !pptr) {
+	if(getpwnam_r(ctxt->name, &p, buf, sizeof(buf), &pptr) != 0) {
 		goto out_err;
 	}
 
+	if (!pptr) {
+		// successfully found nothing
+		ctxt->res->name = NULL;
+		return 0;
+	}
+
 	if(!(ctxt->res->name = strdup(p.pw_name))) {
 		goto out_err;
 	}
@@ -98,10 +104,16 @@ static int group_lookup_fn(lookup_ctxt_t *ctxt) {
 		goto out_err;
 	}
 
-	if(getgrnam_r(ctxt->name, &g, buf, sizeof(buf), &gptr) != 0 || !gptr) {
+	if(getgrnam_r(ctxt->name, &g, buf, sizeof(buf), &gptr) != 0) {
 		goto out_err;
 	}
 
+	if (!gptr) {
+		// successfully found nothing
+		ctxt->res->name = NULL;
+		return 0;
+	}
+
 	if(!(ctxt->res->name = strdup(g.gr_name))) {
 		goto out_err;
 	}

internal/exec/util/user_group_lookup.go

@@ -37,7 +37,7 @@ func (u Util) userLookup(name string) (*user.User, error) {
 	}
 
 	if res.name == nil {
-		return nil, fmt.Errorf("user %q not found", name)
+		return nil, user.UnknownUserError(fmt.Sprintf("user %q not found", name))
 	}
 
 	homedir, err := u.JoinPath(C.GoString(res.home))
@@ -67,7 +67,7 @@ func (u Util) groupLookup(name string) (*user.Group, error) {
 	}
 
 	if res.name == nil {
-		return nil, fmt.Errorf("user %q not found", name)
+		return nil, user.UnknownGroupError(fmt.Sprintf("group %q not found", name))
 	}
 
 	grp := &user.Group{