Add a podmanSocket command with hardcoded uid 199

Add a test to validate subid generation

main.go

@@ -24,7 +24,11 @@ const (
 	G = 1024 * 1024 * 1024
 )
 
+// Setup ensures that everything needed for running podman under the given uid is setup
+// new{u,g}idmap is handled separately
+// Note: This should be called while still root (before MustDropPrivileges) and must be called after any use of the GOKRAZY_FIRST_START environment variable
 func Setup(uid int) error {
+	// Needed so that calls to to podman which in turn call new{u,g}idmap will succeed
 	os.Unsetenv("GOKRAZY_FIRST_START")
 	err := os.Mkdir("/var/run/user", 0o755)
 	if err != nil && !errors.Is(err, os.ErrExist) {
@@ -174,7 +178,7 @@ func IsMounted(mountpoint string) (bool, error) {
 		return false, err
 	}
 
-	for _, line := range strings.Split(strings.TrimSpace(string(b)), "\n") {
+	for line := range strings.SplitSeq(strings.TrimSpace(string(b)), "\n") {
 		parts := strings.Fields(line)
 		if len(parts) < 5 {
 			continue

newgidmap/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"log"
 	"os"
 
 	"gitea.narnian.us/lordwelch/Podman"
@@ -8,7 +9,14 @@ import (
 
 func main() {
 	if os.Getenv("GOKRAZY_FIRST_START") == "1" {
-		Podman.WriteSubids("/etc/subgid")
+		subidContent, err := Podman.GetSubids("/etc/subgid")
+		if err != nil {
+			log.Printf("Unable to generate /etc/subgid successfully, podman will probably not work: %s", err)
+		}
+		err = os.WriteFile("/etc/subgid", subidContent, 0o644)
+		if err != nil {
+			log.Printf("Unable to write to /etc/subgid, podman will probably not work: %s", err)
+		}
 		os.Exit(125)
 	}
 	Podman.NewIDMap("gid_map")

newidmap.go

@@ -7,6 +7,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 	"syscall"
@@ -56,34 +57,39 @@ func NewIDMap(idMapName string) {
 		log.Fatal("You aren't allowed to do that :-P")
 	}
 	var (
-		user    Passwd
-		subid   moby_user.SubID
-		passwds []Passwd = LoadAllPasswd()
+		// This will get overwritten by /etc/passwd if we read subids from files
+		user = Passwd{
+			User: os.Getenv("USER"),
+			UID:  int(fstat.Uid),
+			GID:  int(fstat.Gid),
+		}
+		subid = generateSubid(int64(fstat.Uid))
 	)
-	subidstart := subidStart
-	for _, u := range passwds {
-		if u.UID == int(fstat.Uid) {
-			user = u
-			subid = moby_user.SubID{
-				Name:  user.User,
-				SubID: subidstart,
-				Count: subidCount,
+	subid.Name = user.User
+
+	if subidUseFile {
+		passwds, err := LoadAllPasswd()
+		if err != nil {
+			// Continue because we don't actually want to fail if there is no /etc/passwd
+			// This command assumes a static mapping of subids based on the current uid. Which is already verified above
+			log.Println(err)
+		}
+		for _, u := range passwds {
+			if u.UID == int(fstat.Uid) {
+				user = u
 			}
 		}
-		subidstart += subidCount
-	}
-	if user.User == "" {
-		log.Fatalf("Unable to find user")
-	}
-	if subidUseFile {
+		if user.User == "" {
+			log.Fatalf("Unable to find user")
+		}
 		if idMapName == "uid_map" {
 			subid, err = getSubIDs("/etc/subuid", user.User, strconv.Itoa(user.UID))
 		} else {
 			subid, err = getSubIDs("/etc/subgid", user.User, strconv.Itoa(user.GID))
 		}
-	}
-	if err != nil {
-		log.Fatalf("Unable to get subid map for the user: %v", err)
+		if err != nil {
+			log.Fatalf("Unable to get subid map for the user: %v", err)
+		}
 	}
 	idmaps, err := getIDMaps(int64(user.UID), subid, args)
 	if err != nil {
@@ -118,19 +124,28 @@ func NewIDMap(idMapName string) {
 	}
 }
 
-func WriteSubids(file string) error {
+func GetSubids(passwd string) ([]byte, error) {
 	buf := &bytes.Buffer{}
-	passwds := LoadAllPasswd()
-	subidstart := subidStart
+	passwds, err := LoadAllPasswd(passwd)
+	if err != nil { // Only errors are io errors reading /etc/passwd
+		return nil, err
+	}
+	sort.Slice(passwds, func(i, j int) bool { return passwds[i].UID < passwds[j].UID })
 	for _, passwd := range passwds {
-		fmt.Fprintf(buf, "%s:%d:%d\n", passwd.User, subidstart, subidCount)
-		subidstart += subidCount
+		subid := generateSubid(int64(passwd.UID))
+		_, err := fmt.Fprintf(buf, "%s:%d:%d\n", passwd.User, subid.SubID, subid.Count)
+		if err != nil {
+			return nil, err
+		}
 	}
-	err := os.WriteFile(file, buf.Bytes(), 0o644)
-	if err != nil {
-		return err
+	return buf.Bytes(), nil
+}
+
+func generateSubid(id int64) moby_user.SubID {
+	return moby_user.SubID{
+		SubID: subidStart + (subidCount * id),
+		Count: subidCount,
 	}
-	return nil
 }
 
 func getIDMaps(id int64, subid moby_user.SubID, args []string) ([]moby_user.IDMap, error) {

newidmap_test.go

@@ -0,0 +1,38 @@
+package Podman_test
+
+import (
+	"os"
+	"testing"
+
+	"gitea.narnian.us/lordwelch/Podman"
+)
+
+// passwdContent is specifically not in order
+const passwdContent = `root:x:0:0:root:/perm/home:/perm/bin/bash
+vw:x:2:2:vw:/perm/home/vw:/bin/nologin
+jellyfin:x:1:1:jellyfin:/perm/home/jellyfin:/bin/nologin
+nzbget:x:3:3:nzbget:/perm/home/nzbget:/bin/nologin
+`
+
+// expected is always in uid order
+const expected = `root:200:65536
+jellyfin:65736:65536
+vw:131272:65536
+nzbget:196808:65536
+`
+
+func TestGetSubids(t *testing.T) {
+	tmpDir := t.TempDir()
+	passwd := tmpDir + "/passwd"
+	err := os.WriteFile(passwd, []byte(passwdContent), 0o644)
+	if err != nil {
+		t.Fatalf("Unable to write %s: %s", passwd, err)
+	}
+	ids, err := Podman.GetSubids(passwd)
+	if err != nil {
+		t.Fatal("Unable to generate subids", err)
+	}
+	if got, want := string(ids), expected; got != want {
+		t.Errorf("GetSubids: unexpected result: got %q, want %q", got, want)
+	}
+}

newuidmap/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"log"
 	"os"
 
 	"gitea.narnian.us/lordwelch/Podman"
@@ -8,7 +9,14 @@ import (
 
 func main() {
 	if os.Getenv("GOKRAZY_FIRST_START") == "1" {
-		Podman.WriteSubids("/etc/subuid")
+		subidContent, err := Podman.GetSubids("/etc/subuid")
+		if err != nil {
+			log.Printf("Unable to generate /etc/subuid successfully, podman will probably not work: %s", err)
+		}
+		err = os.WriteFile("/etc/subuid", subidContent, 0o644)
+		if err != nil {
+			log.Printf("Unable to write to /etc/subuid, podman will probably not work: %s", err)
+		}
 		os.Exit(125)
 	}
 	Podman.NewIDMap("uid_map")

podmanSocket/main.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"log"
+	"os"
+	"syscall"
+
+	"gitea.narnian.us/lordwelch/Podman"
+)
+
+func main() {
+	Podman.Setup(199) // subuids start at 200
+	Podman.MustDropPrivileges(Podman.Passwd{
+		User:  "podmanSocket",
+		UID:   199,
+		GID:   199,
+		Home:  "/perm/home/podmanSocket",
+		Shell: "/bin/sh",
+	})
+
+	args := []string{
+		"/user/podman", "system", "--log-level=debug", "service", "--time=0", "unix:///run/podman.sock",
+	}
+	err := syscall.Exec("/user/podman", args, os.Environ())
+	if err != nil {
+		log.Fatalf("failed to start podman: %v", err)
+	}
+}

privDrop.go

@@ -1,6 +1,7 @@
 package Podman
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"path/filepath"
@@ -70,8 +71,9 @@ type Passwd struct {
 func MustDropPrivileges(passwd Passwd, caps ...string) {
 	err := os.Chown(passwd.Home, passwd.UID, passwd.GID)
 	if err != nil {
-		log.Print("Failed to chown home directory", os.Getenv("HOME"))
+		log.Printf("Failed to chown home directory %s", passwd.Home)
 	}
+	os.Setenv("HOME", passwd.Home)
 	os.Setenv("USER", passwd.User)
 	c := cap.GetProc()
 	if os.Getenv("PRIVILEGES_DROPPED") == "1" {
@@ -141,11 +143,18 @@ func LoadPasswd() Passwd {
 	}
 	return passwd
 }
-func LoadAllPasswd() []Passwd {
+
+// LoadAllPasswd reads /etc/passwd by default.
+// If a string is passed the first argument is used as the path instead of /etc/passwd
+func LoadAllPasswd(passwd ...string) ([]Passwd, error) {
 	var passwds []Passwd
-	b, err := os.ReadFile("/etc/passwd")
+	var passwdFile = "/etc/passwd"
+	if len(passwd) > 0 {
+		passwdFile = passwd[0]
+	}
+	b, err := os.ReadFile(passwdFile)
 	if err != nil {
-		return passwds
+		return passwds, fmt.Errorf("Unable to read /etc/passwd: %w", err)
 	}
 	for line := range strings.SplitSeq(string(b), "\n") {
 		fields := strings.SplitN(line, ":", 7)
@@ -168,5 +177,5 @@ func LoadAllPasswd() []Passwd {
 		passwd.Shell = fields[6]
 		passwds = append(passwds, passwd)
 	}
-	return passwds
+	return passwds, nil
 }