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net/interfaces: better handle multiple interfaces in LikelyHomeRouterIP

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Currently, we get the "likely home router" gateway IP and then iterate
through all IPs for all interfaces trying to match IPs to determine the
source IP. However, on many platforms we know what interface the gateway
is through, and thus we don't need to iterate through all interfaces
checking IPs. Instead, use the IP address of the associated interface.

This better handles the case where we have multiple interfaces on a
system all connected to the same gateway, and where the first interface
that we visit (as iterated by ForeachInterfaceAddress) isn't also the
default internet route.

Updates #8992

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I8632f577f1136930f4ec60c76376527a19a47d1f
This commit is contained in:
Andrew Dunham
2023-12-19 16:27:52 -05:00
parent 7a2eb22e94
commit 01286af82b
6 changed files with 83 additions and 25 deletions
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32
net/interfaces/interfaces_linux.go
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@ -45,14 +45,14 @@ Iface Destination Gateway Flags RefCnt Use Metric Mask
ens18 00000000 0100000A 0003 0 0 0 00000000 0 0 0
ens18 0000000A 00000000 0001 0 0 0 0000FFFF 0 0 0
*/
func likelyHomeRouterIPLinux() (ret netip.Addr, ok bool) {
func likelyHomeRouterIPLinux() (ret netip.Addr, myIP netip.Addr, ok bool) {
if procNetRouteErr.Load() {
// If we failed to read /proc/net/route previously, don't keep trying.
// But if we're on Android, go into the Android path.
if runtime.GOOS == "android" {
return likelyHomeRouterIPAndroid()
}
return ret, false
return ret, myIP, false
}
lineNum := 0
var f []mem.RO
@ -99,7 +99,27 @@ func likelyHomeRouterIPLinux() (ret netip.Addr, ok bool) {
log.Printf("interfaces: failed to read /proc/net/route: %v", err)
}
if ret.IsValid() {
return ret, true
// Try to get the local IP of the interface associated with
// this route to short-circuit finding the IP associated with
// this gateway. This isn't fatal if it fails.
if len(f) > 0 && !disableLikelyHomeRouterIPSelf() {
ForeachInterface(func(ni Interface, pfxs []netip.Prefix) {
// Ensure this is the same interface
if !f[0].EqualString(ni.Name) {
return
}
// Find the first IPv4 address and use it.
for _, pfx := range pfxs {
if addr := pfx.Addr(); addr.Is4() {
myIP = addr
break
}
}
})
}
return ret, myIP, true
}
if lineNum >= maxProcNetRouteRead {
// If we went over our line limit without finding an answer, assume
@ -113,12 +133,12 @@ func likelyHomeRouterIPLinux() (ret netip.Addr, ok bool) {
// find one in the future.
procNetRouteErr.Store(true)
}
return netip.Addr{}, false
return netip.Addr{}, netip.Addr{}, false
}
// Android apps don't have permission to read /proc/net/route, at
// least on Google devices and the Android emulator.
func likelyHomeRouterIPAndroid() (ret netip.Addr, ok bool) {
func likelyHomeRouterIPAndroid() (ret netip.Addr, _ netip.Addr, ok bool) {
cmd := exec.Command("/system/bin/ip", "route", "show", "table", "0")
out, err := cmd.StdoutPipe()
if err != nil {
@ -148,7 +168,7 @@ func likelyHomeRouterIPAndroid() (ret netip.Addr, ok bool) {
})
cmd.Process.Kill()
cmd.Wait()
return ret, ret.IsValid()
return ret, netip.Addr{}, ret.IsValid()
}
func defaultRoute() (d DefaultRouteDetails, err error) {