[PATCH wireguard-go] tun: avoid leaking sock fd in CreateTUN error cases

[PATCH wireguard-go] tun: avoid leaking sock fd in CreateTUN error cases

[Tobias Klauser]

At these points, the socket file descriptor is not yet wrapped in an
*os.File, so it needs to be closed explicitly on error.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
---
 tun/tun_darwin.go |  6 ++++--
 tun/tun_linux.go  | 11 +++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/tun/tun_darwin.go b/tun/tun_darwin.go
index a703c8c34eac..35d3085747cc 100644
--- a/tun/tun_darwin.go
+++ b/tun/tun_darwin.go
@@ -108,7 +108,6 @@ func CreateTUN(name string, mtu int) (Device, error) {
 	}
 
 	fd, err := unix.Socket(unix.AF_SYSTEM, unix.SOCK_DGRAM, 2)
-
 	if err != nil {
 		return nil, err
 	}
@@ -117,6 +116,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 	copy(ctlInfo.Name[:], []byte(utunControlName))
 	err = unix.IoctlCtlInfo(fd, ctlInfo)
 	if err != nil {
+		unix.Close(fd)
 		return nil, fmt.Errorf("IoctlGetCtlInfo: %w", err)
 	}
 
@@ -127,11 +127,13 @@ func CreateTUN(name string, mtu int) (Device, error) {
 
 	err = unix.Connect(fd, sc)
 	if err != nil {
+		unix.Close(fd)
 		return nil, err
 	}
 
-	err = syscall.SetNonblock(fd, true)
+	err = unix.SetNonblock(fd, true)
 	if err != nil {
+		unix.Close(fd)
 		return nil, err
 	}
 	tun, err := CreateTUNFromFile(os.NewFile(uintptr(fd), ""), mtu)
diff --git a/tun/tun_linux.go b/tun/tun_linux.go
index 466a805671c1..1cc84cba0ee5 100644
--- a/tun/tun_linux.go
+++ b/tun/tun_linux.go
@@ -419,6 +419,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 	var flags uint16 = unix.IFF_TUN // | unix.IFF_NO_PI (disabled for TUN status hack)
 	nameBytes := []byte(name)
 	if len(nameBytes) >= unix.IFNAMSIZ {
+		unix.Close(nfd)
 		return nil, fmt.Errorf("interface name too long: %w", unix.ENAMETOOLONG)
 	}
 	copy(ifr[:], nameBytes)
@@ -431,17 +432,19 @@ func CreateTUN(name string, mtu int) (Device, error) {
 		uintptr(unsafe.Pointer(&ifr[0])),
 	)
 	if errno != 0 {
+		unix.Close(nfd)
 		return nil, errno
 	}
-	err = unix.SetNonblock(nfd, true)
-
-	// Note that the above -- open,ioctl,nonblock -- must happen prior to handing it to netpoll as below this line.
 
-	fd := os.NewFile(uintptr(nfd), cloneDevicePath)
+	err = unix.SetNonblock(nfd, true)
 	if err != nil {
+		unix.Close(nfd)
 		return nil, err
 	}
 
+	// Note that the above -- open,ioctl,nonblock -- must happen prior to handing it to netpoll as below this line.
+
+	fd := os.NewFile(uintptr(nfd), cloneDevicePath)
 	return CreateTUNFromFile(fd, mtu)
 }
 
-- 
2.33.0

Re: [PATCH wireguard-go] tun: avoid leaking sock fd in CreateTUN error cases

[Jason A. Donenfeld]

Applied, thanks! I'm curious: is this a bug you ran into somewhere?

Re: [PATCH wireguard-go] tun: avoid leaking sock fd in CreateTUN error cases

[Tobias Klauser]

On 2021-09-23 at 17:54:20 +0200, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> Applied, thanks! I'm curious: is this a bug you ran into somewhere?

I've not seen this causing problems with wireguard-go specifically, but
have seen issues with leaked fds elsewhere. So by now I'm attentive of
the pattern and send fixes where I notice it :)