conn, device, tun: set CLOEXEC on fds

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

6 files changed, 36 insertions, 24 deletions

diff --git a/conn/bind_linux.go b/conn/bind_linux.go
index f11f031..03e8707 100644
--- a/conn/bind_linux.go
+++ b/conn/bind_linux.go
@@ -331,7 +331,7 @@ func create4(port uint16) (int, uint16, error) {
 
 	fd, err := unix.Socket(
 		unix.AF_INET,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {
@@ -373,7 +373,7 @@ func create6(port uint16) (int, uint16, error) {
 
 	fd, err := unix.Socket(
 		unix.AF_INET6,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {
diff --git a/device/sticky_linux.go b/device/sticky_linux.go
index 6193ea3..97c14b5 100644
--- a/device/sticky_linux.go
+++ b/device/sticky_linux.go
@@ -204,7 +204,7 @@ func (device *Device) routineRouteListener(bind conn.Bind, netlinkSock int, netl
 }
 
 func createNetlinkRouteSocket() (int, error) {
-	sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW, unix.NETLINK_ROUTE)
+	sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW|unix.SOCK_CLOEXEC, unix.NETLINK_ROUTE)
 	if err != nil {
 		return -1, err
 	}
diff --git a/tun/tun_darwin.go b/tun/tun_darwin.go
index 94bbfa6..1ce8a46 100644
--- a/tun/tun_darwin.go
+++ b/tun/tun_darwin.go
@@ -107,7 +107,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 		}
 	}
 
-	fd, err := unix.Socket(unix.AF_SYSTEM, unix.SOCK_DGRAM, 2)
+	fd, err := socketCloexec(unix.AF_SYSTEM, unix.SOCK_DGRAM, 2)
 	if err != nil {
 		return nil, err
 	}
@@ -173,7 +173,7 @@ func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
 		return nil, err
 	}
 
-	tun.routeSocket, err = unix.Socket(unix.AF_ROUTE, unix.SOCK_RAW, unix.AF_UNSPEC)
+	tun.routeSocket, err = socketCloexec(unix.AF_ROUTE, unix.SOCK_RAW, unix.AF_UNSPEC)
 	if err != nil {
 		tun.tunFile.Close()
 		return nil, err
@@ -276,7 +276,7 @@ func (tun *NativeTun) Close() error {
 }
 
 func (tun *NativeTun) setMTU(n int) error {
-	fd, err := unix.Socket(
+	fd, err := socketCloexec(
 		unix.AF_INET,
 		unix.SOCK_DGRAM,
 		0,
@@ -299,7 +299,7 @@ func (tun *NativeTun) setMTU(n int) error {
 }
 
 func (tun *NativeTun) MTU() (int, error) {
-	fd, err := unix.Socket(
+	fd, err := socketCloexec(
 		unix.AF_INET,
 		unix.SOCK_DGRAM,
 		0,
@@ -317,3 +317,15 @@ func (tun *NativeTun) MTU() (int, error) {
 
 	return int(ifr.MTU), nil
 }
+
+func socketCloexec(family, sotype, proto int) (fd int, err error) {
+	// See go/src/net/sys_cloexec.go for background.
+	syscall.ForkLock.RLock()
+	defer syscall.ForkLock.RUnlock()
+
+	fd, err = unix.Socket(family, sotype, proto)
+	if err == nil {
+		unix.CloseOnExec(fd)
+	}
+	return
+}
diff --git a/tun/tun_freebsd.go b/tun/tun_freebsd.go
index dc9eb3e..e1e8986 100644
--- a/tun/tun_freebsd.go
+++ b/tun/tun_freebsd.go
@@ -143,7 +143,7 @@ func tunName(fd uintptr) (string, error) {
 
 // Destroy a named system interface
 func tunDestroy(name string) error {
-	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
 	if err != nil {
 		return err
 	}
@@ -170,7 +170,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 		return nil, fmt.Errorf("interface %s already exists", name)
 	}
 
-	tunFile, err := os.OpenFile("/dev/tun", unix.O_RDWR, 0)
+	tunFile, err := os.OpenFile("/dev/tun", unix.O_RDWR|unix.O_CLOEXEC, 0)
 	if err != nil {
 		return nil, err
 	}
@@ -213,7 +213,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 	// Disable link-local v6, not just because WireGuard doesn't do that anyway, but
 	// also because there are serious races with attaching and detaching LLv6 addresses
 	// in relation to interface lifetime within the FreeBSD kernel.
-	confd6, err := unix.Socket(unix.AF_INET6, unix.SOCK_DGRAM, 0)
+	confd6, err := unix.Socket(unix.AF_INET6, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
 	if err != nil {
 		tunFile.Close()
 		tunDestroy(assignedName)
@@ -238,7 +238,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 	}
 
 	if name != "" {
-		confd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
+		confd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
 		if err != nil {
 			tunFile.Close()
 			tunDestroy(assignedName)
@@ -295,7 +295,7 @@ func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
 		return nil, err
 	}
 
-	tun.routeSocket, err = unix.Socket(unix.AF_ROUTE, unix.SOCK_RAW, unix.AF_UNSPEC)
+	tun.routeSocket, err = unix.Socket(unix.AF_ROUTE, unix.SOCK_RAW|unix.SOCK_CLOEXEC, unix.AF_UNSPEC)
 	if err != nil {
 		tun.tunFile.Close()
 		return nil, err
@@ -397,7 +397,7 @@ func (tun *NativeTun) Close() error {
 }
 
 func (tun *NativeTun) setMTU(n int) error {
-	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
 	if err != nil {
 		return err
 	}
@@ -414,7 +414,7 @@ func (tun *NativeTun) setMTU(n int) error {
 }
 
 func (tun *NativeTun) MTU() (int, error) {
-	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
 	if err != nil {
 		return 0, err
 	}
diff --git a/tun/tun_linux.go b/tun/tun_linux.go
index fbb8585..90cb2df 100644
--- a/tun/tun_linux.go
+++ b/tun/tun_linux.go
@@ -99,7 +99,7 @@ func (tun *NativeTun) routineHackListener() {
 }
 
 func createNetlinkSocket() (int, error) {
-	sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW, unix.NETLINK_ROUTE)
+	sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW|unix.SOCK_CLOEXEC, unix.NETLINK_ROUTE)
 	if err != nil {
 		return -1, err
 	}
@@ -194,7 +194,7 @@ func (tun *NativeTun) routineNetlinkListener() {
 func getIFIndex(name string) (int32, error) {
 	fd, err := unix.Socket(
 		unix.AF_INET,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {
@@ -228,7 +228,7 @@ func (tun *NativeTun) setMTU(n int) error {
 	// open datagram socket
 	fd, err := unix.Socket(
 		unix.AF_INET,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {
@@ -264,7 +264,7 @@ func (tun *NativeTun) MTU() (int, error) {
 	// open datagram socket
 	fd, err := unix.Socket(
 		unix.AF_INET,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {
@@ -400,7 +400,7 @@ func (tun *NativeTun) Close() error {
 }
 
 func CreateTUN(name string, mtu int) (Device, error) {
-	nfd, err := unix.Open(cloneDevicePath, os.O_RDWR, 0)
+	nfd, err := unix.Open(cloneDevicePath, unix.O_RDWR|unix.O_CLOEXEC, 0)
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil, fmt.Errorf("CreateTUN(%q) failed; %s does not exist", name, cloneDevicePath)
diff --git a/tun/tun_openbsd.go b/tun/tun_openbsd.go
index ff845bc..b7a33b5 100644
--- a/tun/tun_openbsd.go
+++ b/tun/tun_openbsd.go
@@ -114,10 +114,10 @@ func CreateTUN(name string, mtu int) (Device, error) {
 	var err error
 
 	if ifIndex != -1 {
-		tunfile, err = os.OpenFile(fmt.Sprintf("/dev/tun%d", ifIndex), unix.O_RDWR, 0)
+		tunfile, err = os.OpenFile(fmt.Sprintf("/dev/tun%d", ifIndex), unix.O_RDWR|unix.O_CLOEXEC, 0)
 	} else {
 		for ifIndex = 0; ifIndex < 256; ifIndex++ {
-			tunfile, err = os.OpenFile(fmt.Sprintf("/dev/tun%d", ifIndex), unix.O_RDWR, 0)
+			tunfile, err = os.OpenFile(fmt.Sprintf("/dev/tun%d", ifIndex), unix.O_RDWR|unix.O_CLOEXEC, 0)
 			if err == nil || !errors.Is(err, syscall.EBUSY) {
 				break
 			}
@@ -165,7 +165,7 @@ func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
 		return nil, err
 	}
 
-	tun.routeSocket, err = unix.Socket(unix.AF_ROUTE, unix.SOCK_RAW, unix.AF_UNSPEC)
+	tun.routeSocket, err = unix.Socket(unix.AF_ROUTE, unix.SOCK_RAW|unix.SOCK_CLOEXEC, unix.AF_UNSPEC)
 	if err != nil {
 		tun.tunFile.Close()
 		return nil, err
@@ -270,7 +270,7 @@ func (tun *NativeTun) setMTU(n int) error {
 
 	fd, err := unix.Socket(
 		unix.AF_INET,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {
@@ -304,7 +304,7 @@ func (tun *NativeTun) MTU() (int, error) {
 
 	fd, err := unix.Socket(
 		unix.AF_INET,
-		unix.SOCK_DGRAM,
+		unix.SOCK_DGRAM|unix.SOCK_CLOEXEC,
 		0,
 	)
 	if err != nil {