user: skip records with invalid numeric IDs

user/user.go

@@ -56,13 +56,15 @@ type IDMap struct {
 	Count    int64
 }
 
-func parseLine(line []byte, v ...any) {
-	parseParts(bytes.Split(line, []byte(":")), v...)
+func parseLine(line []byte, v ...any) bool {
+	return parseParts(bytes.Split(line, []byte(":")), v...)
 }
 
-func parseParts(parts [][]byte, v ...any) {
+func parseParts(parts [][]byte, v ...any) bool {
+	// Report invalid numeric fields so callers do not accept them as ID zero.
+	valid := true
 	if len(parts) == 0 {
-		return
+		return true
 	}
 
 	for i, p := range parts {
@@ -78,10 +80,17 @@ func parseParts(parts [][]byte, v ...any) {
 		case *string:
 			*e = string(p)
 		case *int:
-			// "numbers", with conversion errors ignored because of some misbehaving configuration files.
-			*e, _ = strconv.Atoi(string(p))
+			id, err := strconv.Atoi(string(p))
+			*e = id
+			if err != nil {
+				valid = false
+			}
 		case *int64:
-			*e, _ = strconv.ParseInt(string(p), 10, 64)
+			id, err := strconv.ParseInt(string(p), 10, 64)
+			*e = id
+			if err != nil {
+				valid = false
+			}
 		case *[]string:
 			// Comma-separated lists.
 			if len(p) != 0 {
@@ -94,6 +103,8 @@ func parseParts(parts [][]byte, v ...any) {
 			panic(fmt.Sprintf("parseLine only accepts {*string, *int, *int64, *[]string} as arguments! %#v is not a pointer!", e))
 		}
 	}
+
+	return valid
 }
 
 func ParsePasswdFile(path string) ([]User, error) {
@@ -135,7 +146,9 @@ func ParsePasswdFilter(r io.Reader, filter func(User) bool) ([]User, error) {
 		//  root:x:0:0:root:/root:/bin/bash
 		//  adm:x:3:4:adm:/var/adm:/bin/false
 		p := User{}
-		parseLine(line, &p.Name, &p.Pass, &p.Uid, &p.Gid, &p.Gecos, &p.Home, &p.Shell)
+		if !parseLine(line, &p.Name, &p.Pass, &p.Uid, &p.Gid, &p.Gecos, &p.Home, &p.Shell) {
+			continue
+		}
 
 		if filter == nil || filter(p) {
 			out = append(out, p)
@@ -194,7 +207,9 @@ func ParseGroupFilter(r io.Reader, filter func(Group) bool) ([]Group, error) {
 		//  root:x:0:root
 		//  adm:x:4:root,adm,daemon
 		p := Group{}
-		parseLine(line, &p.Name, &p.Pass, &p.Gid, &p.List)
+		if !parseLine(line, &p.Name, &p.Pass, &p.Gid, &p.List) {
+			continue
+		}
 
 		if filter == nil || filter(p) {
 			out = append(out, p)
@@ -501,7 +516,9 @@ func ParseSubIDFilter(r io.Reader, filter func(SubID) bool) ([]SubID, error) {
 
 		// see: man 5 subuid
 		p := SubID{}
-		parseLine(line, &p.Name, &p.SubID, &p.Count)
+		if !parseLine(line, &p.Name, &p.SubID, &p.Count) {
+			continue
+		}
 
 		if filter == nil || filter(p) {
 			out = append(out, p)
@@ -549,7 +566,9 @@ func ParseIDMapFilter(r io.Reader, filter func(IDMap) bool) ([]IDMap, error) {
 
 		// see: man 7 user_namespaces
 		p := IDMap{}
-		parseParts(bytes.Fields(line), &p.ID, &p.ParentID, &p.Count)
+		if !parseParts(bytes.Fields(line), &p.ID, &p.ParentID, &p.Count) {
+			continue
+		}
 
 		if filter == nil || filter(p) {
 			out = append(out, p)

user/user_test.go

@@ -707,3 +707,32 @@ func largeGroup() (res string) {
 	}
 	return b.String()
 }
+
+func TestParsePasswdFilterSkipsInvalidIDs(t *testing.T) {
+	users, err := ParsePasswdFilter(strings.NewReader(`
+root:x:0:0:root:/root:/bin/sh
+bad-uid:x:not-a-uid:10::/:/bin/sh
+bad-gid:x:11:not-a-gid::/:/bin/sh
+overflow:x:999999999999999999999:12::/:/bin/sh
+`), nil)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if len(users) != 1 || users[0].Name != "root" || users[0].Uid != 0 || users[0].Gid != 0 {
+		t.Fatalf("Expected only the valid root entry, got %+v", users)
+	}
+}
+
+func TestParseGroupFilterSkipsInvalidIDs(t *testing.T) {
+	groups, err := ParseGroupFilter(strings.NewReader(`
+root:x:0:root
+bad-gid:x:not-a-gid:root
+overflow:x:999999999999999999999:root
+`), nil)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if len(groups) != 1 || groups[0].Name != "root" || groups[0].Gid != 0 {
+		t.Fatalf("Expected only the valid root entry, got %+v", groups)
+	}
+}