net: avoid unnecessary interface lookup fetching all interface addresses

InterfaceAddrs returns a list of the system's unicast interface addresses.

In order to do so, the function reuses the existing helpers and
list first all addresses with the netlink call RTM_GETADDR, then
all interfaces with RTM_GETLINK, and later it merge both lists
(each address references an interface).

However, the list of interfaces and addresses are obtained at
different times and there can be inconsistencies and, if an
address references an interface that is not present in the list
of interfaces, the function fails with an error.

Since the function InterfaceAddress is only about the system
addresses, there is no need to list all the interfaces, and we can
obtain the list of addresses directly from the netlink call RTM_GETADDR.
There is no need to correlate this list with the list of interfaces, as
the OS is the source of truth and should be the one providing the
consistency between addresses and interfaces.

Fixes #51934

Change-Id: I3b816e8146b1c07fdfe1bf6af338f001ef75734f
Reviewed-on: https://go-review.googlesource.com/c/go/+/635196
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

diff --git a/src/net/interface_linux.go b/src/net/interface_linux.go
index 9112ecc854c74ca4e272c767eb033f899aea949c..7856dae8fc878b72a5444a069b53580498418d63 100644 (file)
--- a/src/net/interface_linux.go
+++ b/src/net/interface_linux.go
@@ -129,22 +129,14 @@ func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
        if err != nil {
                return nil, os.NewSyscallError("parsenetlinkmessage", err)
        }
-       var ift []Interface
-       if ifi == nil {
-               var err error
-               ift, err = interfaceTable(0)
-               if err != nil {
-                       return nil, err
-               }
-       }
-       ifat, err := addrTable(ift, ifi, msgs)
+       ifat, err := addrTable(ifi, msgs)
        if err != nil {
                return nil, err
        }
        return ifat, nil
 }
 
-func addrTable(ift []Interface, ifi *Interface, msgs []syscall.NetlinkMessage) ([]Addr, error) {
+func addrTable(ifi *Interface, msgs []syscall.NetlinkMessage) ([]Addr, error) {
        var ifat []Addr
 loop:
        for _, m := range msgs {
@@ -153,14 +145,7 @@ loop:
                        break loop
                case syscall.RTM_NEWADDR:
                        ifam := (*syscall.IfAddrmsg)(unsafe.Pointer(&m.Data[0]))
-                       if len(ift) != 0 || ifi.Index == int(ifam.Index) {
-                               if len(ift) != 0 {
-                                       var err error
-                                       ifi, err = interfaceByIndex(ift, int(ifam.Index))
-                                       if err != nil {
-                                               return nil, err
-                                       }
-                               }
+                       if ifi == nil || ifi.Index == int(ifam.Index) {
                                attrs, err := syscall.ParseNetlinkRouteAttr(&m)
                                if err != nil {
                                        return nil, os.NewSyscallError("parsenetlinkrouteattr", err)