tun: freebsd: work around numerous kernel panics on shutdown

There are numerous race conditions. But even this will crash it:

while true; do ifconfig tun0 create; ifconfig tun0 destroy; done

It seems like LLv6 is related, which we're not using anyway, so
explicitly disable it on the interface.

diff --git a/tun/tun_freebsd.go b/tun/tun_freebsd.go
index 01a43486fc28be189959f20b2779247691851375..c9c89ef65b252701daf17156857ec745026a2f3b 100644 (file)
--- a/tun/tun_freebsd.go
+++ b/tun/tun_freebsd.go
@@ -19,9 +19,19 @@ import (
 
 // _TUNSIFHEAD, value derived from sys/net/{if_tun,ioccom}.h
 // const _TUNSIFHEAD = ((0x80000000) | (((4) & ((1 << 13) - 1) ) << 16) | (uint32(byte('t')) << 8) | (96))
-const _TUNSIFHEAD = 0x80047460
-const _TUNSIFMODE = 0x8004745e
-const _TUNSIFPID = 0x2000745f
+const (
+       _TUNSIFHEAD = 0x80047460
+       _TUNSIFMODE = 0x8004745e
+       _TUNSIFPID  = 0x2000745f
+)
+
+//TODO: move into x/sys/unix
+const (
+       SIOCGIFINFO_IN6        = 0xc048696c
+       SIOCSIFINFO_IN6        = 0xc048696d
+       ND6_IFF_AUTO_LINKLOCAL = 0x20
+       ND6_IFF_NO_DAD         = 0x100
+)
 
 // Iface status string max len
 const _IFSTATMAX = 800
@@ -32,7 +42,7 @@ const SIZEOF_UINTPTR = 4 << (^uintptr(0) >> 32 & 1)
 type ifreq_ptr struct {
        Name [unix.IFNAMSIZ]byte
        Data uintptr
-       Pad0 [24 - SIZEOF_UINTPTR]byte
+       Pad0 [16 - SIZEOF_UINTPTR]byte
 }
 
 // Structure for iface mtu get/set ioctls
@@ -48,6 +58,23 @@ type ifstat struct {
        Ascii   [_IFSTATMAX]byte
 }
 
+// Structures for nd6 flag manipulation
+type in6_ndireq struct {
+       Name          [unix.IFNAMSIZ]byte
+       Linkmtu       uint32
+       Maxmtu        uint32
+       Basereachable uint32
+       Reachable     uint32
+       Retrans       uint32
+       Flags         uint32
+       Recalctm      int
+       Chlim         uint8
+       Initialized   uint8
+       Randomseed0   [8]byte
+       Randomseed1   [8]byte
+       Randomid      [8]byte
+}
+
 type NativeTun struct {
        name        string
        tunFile     *os.File
@@ -191,23 +218,18 @@ func tunName(fd uintptr) (string, error) {
 
 // Destroy a named system interface
 func tunDestroy(name string) error {
-       // open control socket
+       // Open control socket.
        var fd int
-
        fd, err := unix.Socket(
                unix.AF_INET,
                unix.SOCK_DGRAM,
                0,
        )
-
        if err != nil {
                return err
        }
-
        defer unix.Close(fd)
 
-       // do ioctl call
-
        var ifr [32]byte
        copy(ifr[:], name)
        _, _, errno := unix.Syscall(
@@ -216,7 +238,6 @@ func tunDestroy(name string) error {
                uintptr(unix.SIOCIFDESTROY),
                uintptr(unsafe.Pointer(&ifr[0])),
        )
-
        if errno != 0 {
                return fmt.Errorf("failed to destroy interface %s: %s", name, errno.Error())
        }
@@ -263,33 +284,71 @@ func CreateTUN(name string, mtu int) (TUNDevice, error) {
        })
 
        if errno != 0 {
-               return nil, fmt.Errorf("error %s", errno.Error())
+               tunFile.Close()
+               tunDestroy(assignedName)
+               return nil, fmt.Errorf("Unable to put into IFHEAD mode: %v", errno)
        }
 
-       // Rename tun interface
-
-       // Open control socket
+       // Open control sockets
        confd, err := unix.Socket(
                unix.AF_INET,
                unix.SOCK_DGRAM,
                0,
        )
-
        if err != nil {
+               tunFile.Close()
+               tunDestroy(assignedName)
                return nil, err
        }
-
        defer unix.Close(confd)
+       confd6, err := unix.Socket(
+               unix.AF_INET6,
+               unix.SOCK_DGRAM,
+               0,
+       )
+       if err != nil {
+               tunFile.Close()
+               tunDestroy(assignedName)
+               return nil, err
+       }
+       defer unix.Close(confd6)
 
-       // set up struct for iface rename
+       // 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.
+       var ndireq in6_ndireq
+       copy(ndireq.Name[:], assignedName)
+       _, _, errno = unix.Syscall(
+               unix.SYS_IOCTL,
+               uintptr(confd6),
+               uintptr(SIOCGIFINFO_IN6),
+               uintptr(unsafe.Pointer(&ndireq)),
+       )
+       if errno != 0 {
+               tunFile.Close()
+               tunDestroy(assignedName)
+               return nil, fmt.Errorf("Unable to get nd6 flags for %s: %v", assignedName, errno)
+       }
+       ndireq.Flags = ndireq.Flags &^ ND6_IFF_AUTO_LINKLOCAL
+       ndireq.Flags = ndireq.Flags | ND6_IFF_NO_DAD
+       _, _, errno = unix.Syscall(
+               unix.SYS_IOCTL,
+               uintptr(confd6),
+               uintptr(SIOCSIFINFO_IN6),
+               uintptr(unsafe.Pointer(&ndireq)),
+       )
+       if errno != 0 {
+               tunFile.Close()
+               tunDestroy(assignedName)
+               return nil, fmt.Errorf("Unable to set nd6 flags for %s: %v", assignedName, errno)
+       }
+
+       // Rename the interface
        var newnp [unix.IFNAMSIZ]byte
        copy(newnp[:], name)
-
        var ifr ifreq_ptr
        copy(ifr.Name[:], assignedName)
        ifr.Data = uintptr(unsafe.Pointer(&newnp[0]))
-
-       //do actual ioctl to rename iface
        _, _, errno = unix.Syscall(
                unix.SYS_IOCTL,
                uintptr(confd),
@@ -298,8 +357,8 @@ func CreateTUN(name string, mtu int) (TUNDevice, error) {
        )
        if errno != 0 {
                tunFile.Close()
-               tunDestroy(name)
-               return nil, fmt.Errorf("failed to rename %s to %s: %s", assignedName, name, errno.Error())
+               tunDestroy(assignedName)
+               return nil, fmt.Errorf("Failed to rename %s to %s: %v", assignedName, name, errno)
        }
 
        return CreateTUNFromFile(tunFile, mtu)