Do not resolve remote link address at transport layer

Link address resolution is performed at the link layer (if required) so
we can defer it from the transport layer. When link resolution is
required, packets will be queued and sent once link resolution
completes. If link resolution fails, the transport layer will receive a
control message indicating that the stack failed to route the packet.

tcpip.Endpoint.Write no longer returns a channel now that writes do not
wait for link resolution at the transport layer.

tcpip.ErrNoLinkAddress is no longer used so it is removed.

Removed calls to stack.Route.ResolveWith from the transport layer so
that link resolution is performed when a route is created in response
to an incoming packet (e.g. to complete TCP handshakes or send a RST).

Tests:
- integration_test.TestForwarding
- integration_test.TestTCPLinkResolutionFailure

Fixes #4458

RELNOTES: n/a
PiperOrigin-RevId: 351684158

3 files changed, 5 insertions, 42 deletions

diff --git a/pkg/sentry/socket/netstack/BUILD b/pkg/sentry/socket/netstack/BUILD
index b2206900b..22abca120 100644
--- a/pkg/sentry/socket/netstack/BUILD
+++ b/pkg/sentry/socket/netstack/BUILD
@@ -18,7 +18,6 @@ go_library(
     ],
     deps = [
         "//pkg/abi/linux",
-        "//pkg/amutex",
         "//pkg/binary",
         "//pkg/context",
         "//pkg/log",
diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index 57f224120..94fb425b2 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -36,7 +36,6 @@ import (
 
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/amutex"
 	"gvisor.dev/gvisor/pkg/binary"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/log"
@@ -459,18 +458,10 @@ func (i *ioSequencePayload) DropFirst(n int) {
 // Write implements fs.FileOperations.Write.
 func (s *SocketOperations) Write(ctx context.Context, _ *fs.File, src usermem.IOSequence, _ int64) (int64, error) {
 	f := &ioSequencePayload{ctx: ctx, src: src}
-	n, resCh, err := s.Endpoint.Write(f, tcpip.WriteOptions{})
+	n, err := s.Endpoint.Write(f, tcpip.WriteOptions{})
 	if err == tcpip.ErrWouldBlock {
 		return 0, syserror.ErrWouldBlock
 	}
-
-	if resCh != nil {
-		if err := amutex.Block(ctx, resCh); err != nil {
-			return 0, err
-		}
-		n, _, err = s.Endpoint.Write(f, tcpip.WriteOptions{})
-	}
-
 	if err != nil {
 		return 0, syserr.TranslateNetstackError(err).ToError()
 	}
@@ -526,24 +517,12 @@ func (r *readerPayload) Payload(size int) ([]byte, *tcpip.Error) {
 // ReadFrom implements fs.FileOperations.ReadFrom.
 func (s *SocketOperations) ReadFrom(ctx context.Context, _ *fs.File, r io.Reader, count int64) (int64, error) {
 	f := &readerPayload{ctx: ctx, r: r, count: count}
-	n, resCh, err := s.Endpoint.Write(f, tcpip.WriteOptions{
+	n, err := s.Endpoint.Write(f, tcpip.WriteOptions{
 		// Reads may be destructive but should be very fast,
 		// so we can't release the lock while copying data.
 		Atomic: true,
 	})
 	if err == tcpip.ErrWouldBlock {
-		return 0, syserror.ErrWouldBlock
-	}
-
-	if resCh != nil {
-		if err := amutex.Block(ctx, resCh); err != nil {
-			return 0, err
-		}
-		n, _, err = s.Endpoint.Write(f, tcpip.WriteOptions{
-			Atomic: true, // See above.
-		})
-	}
-	if err == tcpip.ErrWouldBlock {
 		return n, syserror.ErrWouldBlock
 	} else if err != nil {
 		return int64(n), f.err // Propagate error.
@@ -2836,13 +2815,7 @@ func (s *socketOpsCommon) SendMsg(t *kernel.Task, src usermem.IOSequence, to []b
 	}
 
 	v := &ioSequencePayload{t, src}
-	n, resCh, err := s.Endpoint.Write(v, opts)
-	if resCh != nil {
-		if err := t.Block(resCh); err != nil {
-			return 0, syserr.FromError(err)
-		}
-		n, _, err = s.Endpoint.Write(v, opts)
-	}
+	n, err := s.Endpoint.Write(v, opts)
 	dontWait := flags&linux.MSG_DONTWAIT != 0
 	if err == nil && (n >= v.src.NumBytes() || dontWait) {
 		// Complete write.
@@ -2861,7 +2834,7 @@ func (s *socketOpsCommon) SendMsg(t *kernel.Task, src usermem.IOSequence, to []b
 	v.DropFirst(int(n))
 	total := n
 	for {
-		n, _, err = s.Endpoint.Write(v, opts)
+		n, err = s.Endpoint.Write(v, opts)
 		v.DropFirst(int(n))
 		total += n
 
diff --git a/pkg/sentry/socket/netstack/netstack_vfs2.go b/pkg/sentry/socket/netstack/netstack_vfs2.go
index b756bfca0..6f70b02fc 100644
--- a/pkg/sentry/socket/netstack/netstack_vfs2.go
+++ b/pkg/sentry/socket/netstack/netstack_vfs2.go
@@ -16,7 +16,6 @@ package netstack
 
 import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/amutex"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/marshal"
 	"gvisor.dev/gvisor/pkg/marshal/primitive"
@@ -131,18 +130,10 @@ func (s *SocketVFS2) Write(ctx context.Context, src usermem.IOSequence, opts vfs
 	}
 
 	f := &ioSequencePayload{ctx: ctx, src: src}
-	n, resCh, err := s.Endpoint.Write(f, tcpip.WriteOptions{})
+	n, err := s.Endpoint.Write(f, tcpip.WriteOptions{})
 	if err == tcpip.ErrWouldBlock {
 		return 0, syserror.ErrWouldBlock
 	}
-
-	if resCh != nil {
-		if err := amutex.Block(ctx, resCh); err != nil {
-			return 0, err
-		}
-		n, _, err = s.Endpoint.Write(f, tcpip.WriteOptions{})
-	}
-
 	if err != nil {
 		return 0, syserr.TranslateNetstackError(err).ToError()
 	}