Add NETLINK_KOBJECT_UEVENT socket support

NETLINK_KOBJECT_UEVENT sockets send udev-style messages for device events.
gVisor doesn't have any device events, so our sockets don't need to do anything
once created.

systemd's device manager needs to be able to create one of these sockets. It
also wants to install a BPF filter on the socket. Since we'll never send any
messages, the filter would never be invoked, thus we just fake it out.

Fixes #1117
Updates #1119

PiperOrigin-RevId: 278405893

1 files changed, 42 insertions, 0 deletions

diff --git a/pkg/sentry/socket/netlink/socket.go b/pkg/sentry/socket/netlink/socket.go
index 05dac4f0a..4a1b87a9a 100644
--- a/pkg/sentry/socket/netlink/socket.go
+++ b/pkg/sentry/socket/netlink/socket.go
@@ -54,6 +54,8 @@ const (
 	maxSendBufferSize = 4 << 20 // 4MB
 )
 
+var errNoFilter = syserr.New("no filter attached", linux.ENOENT)
+
 // netlinkSocketDevice is the netlink socket virtual device.
 var netlinkSocketDevice = device.NewAnonDevice()
 
@@ -108,6 +110,12 @@ type Socket struct {
 
 	// passcred indicates if this socket wants SCM credentials.
 	passcred bool
+
+	// filter indicates that this socket has a BPF filter "installed".
+	//
+	// TODO(gvisor.dev/issue/1119): We don't actually support filtering,
+	// this is just bookkeeping for tracking add/remove.
+	filter bool
 }
 
 var _ socket.Socket = (*Socket)(nil)
@@ -400,6 +408,40 @@ func (s *Socket) SetSockOpt(t *kernel.Task, level int, name int, opt []byte) *sy
 			s.mu.Unlock()
 			return nil
 
+		case linux.SO_ATTACH_FILTER:
+			// TODO(gvisor.dev/issue/1119): We don't actually
+			// support filtering. If this socket can't ever send
+			// messages, then there is nothing to filter and we can
+			// advertise support. Otherwise, be conservative and
+			// return an error.
+			if s.protocol.CanSend() {
+				socket.SetSockOptEmitUnimplementedEvent(t, name)
+				return syserr.ErrProtocolNotAvailable
+			}
+
+			s.mu.Lock()
+			s.filter = true
+			s.mu.Unlock()
+			return nil
+
+		case linux.SO_DETACH_FILTER:
+			// TODO(gvisor.dev/issue/1119): See above.
+			if s.protocol.CanSend() {
+				socket.SetSockOptEmitUnimplementedEvent(t, name)
+				return syserr.ErrProtocolNotAvailable
+			}
+
+			s.mu.Lock()
+			filter := s.filter
+			s.filter = false
+			s.mu.Unlock()
+
+			if !filter {
+				return errNoFilter
+			}
+
+			return nil
+
 		default:
 			socket.SetSockOptEmitUnimplementedEvent(t, name)
 		}