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net/interfaces: improve default route detection

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Instead of treating any interface with a non-ifscope route as a
potential default gateway, now verify that a given route is
actually a default route (0.0.0.0/0 or ::/0).

Fixes #5879

Signed-off-by: Anton Tolchanov <anton@tailscale.com>
This commit is contained in:
Anton Tolchanov
2022-10-14 16:16:55 +01:00
committed by Anton Tolchanov
parent 9c2ad7086c
commit d499afac78
2 changed files with 74 additions and 38 deletions
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32
net/interfaces/interfaces_darwin_test.go
View File

@@ -17,17 +17,31 @@ import (
func TestLikelyHomeRouterIPSyscallExec(t *testing.T) {
syscallIP, syscallOK := likelyHomeRouterIPBSDFetchRIB()
netstatIP, netstatOK := likelyHomeRouterIPDarwinExec()
netstatIP, netstatIf, netstatOK := likelyHomeRouterIPDarwinExec()
if syscallOK != netstatOK || syscallIP != netstatIP {
t.Errorf("syscall() = %v, %v, netstat = %v, %v",
syscallIP, syscallOK,
netstatIP, netstatOK,
)
}
if !syscallOK {
return
}
def, err := defaultRoute()
if err != nil {
t.Errorf("defaultRoute() error: %v", err)
}
if def.InterfaceName != netstatIf {
t.Errorf("syscall default route interface %s differs from netstat %s", def.InterfaceName, netstatIf)
}
}
/*
Parse out 10.0.0.1 from:
Parse out 10.0.0.1 and en0 from:
$ netstat -r -n -f inet
Routing tables
@@ -40,12 +54,12 @@ default link#14 UCSI utun2
10.0.0.1/32 link#4 UCS en0 !
...
*/
func likelyHomeRouterIPDarwinExec() (ret netip.Addr, ok bool) {
func likelyHomeRouterIPDarwinExec() (ret netip.Addr, netif string, ok bool) {
if version.IsMobile() {
// Don't try to do subprocesses on iOS. Ends up with log spam like:
// kernel: "Sandbox: IPNExtension(86580) deny(1) process-fork"
// This is why we have likelyHomeRouterIPDarwinSyscall.
return ret, false
return ret, "", false
}
cmd := exec.Command("/usr/sbin/netstat", "-r", "-n", "-f", "inet")
stdout, err := cmd.StdoutPipe()
@@ -64,22 +78,26 @@ func likelyHomeRouterIPDarwinExec() (ret netip.Addr, ok bool) {
return nil
}
f = mem.AppendFields(f[:0], line)
if len(f) < 3 || !f[0].EqualString("default") {
if len(f) < 4 || !f[0].EqualString("default") {
return nil
}
ipm, flagsm := f[1], f[2]
ipm, flagsm, netifm := f[1], f[2], f[3]
if !mem.Contains(flagsm, mem.S("G")) {
return nil
}
if mem.Contains(flagsm, mem.S("I")) {
return nil
}
ip, err := netip.ParseAddr(string(mem.Append(nil, ipm)))
if err == nil && ip.IsPrivate() {
ret = ip
netif = netifm.StringCopy()
// We've found what we're looking for.
return errStopReadingNetstatTable
}
return nil
})
return ret, ret.IsValid()
return ret, netif, ret.IsValid()
}
func TestFetchRoutingTable(t *testing.T) {