Port SCM Rights to VFS2.

Fixes #1477.

PiperOrigin-RevId: 308317511

pkg/sentry/fs/host/control.go

@@ -23,6 +23,8 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 )
 
+// LINT.IfChange
+
 type scmRights struct {
 	fds []int
 }
@@ -32,8 +34,6 @@ func newSCMRights(fds []int) control.SCMRights {
 }
 
 // Files implements control.SCMRights.Files.
-//
-// TODO(gvisor.dev/issue/2017): Port to VFS2.
 func (c *scmRights) Files(ctx context.Context, max int) (control.RightsFiles, bool) {
 	n := max
 	var trunc bool
@@ -93,3 +93,5 @@ func fdsToFiles(ctx context.Context, fds []int) []*fs.File {
 	}
 	return files
 }
+
+// LINT.ThenChange(../../fsimpl/host/control.go)

pkg/sentry/fsimpl/host/BUILD

@@ -5,6 +5,7 @@ licenses(["notice"])
 go_library(
     name = "host",
     srcs = [
+        "control.go",
         "host.go",
         "ioctl_unsafe.go",
         "tty.go",
@@ -23,6 +24,8 @@ go_library(
         "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/memmap",
+        "//pkg/sentry/socket/control",
+        "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/unimpl",
         "//pkg/sentry/vfs",
         "//pkg/sync",

pkg/sentry/fsimpl/host/control.go

@@ -0,0 +1,96 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package host
+
+import (
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/control"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+type scmRights struct {
+	fds []int
+}
+
+func newSCMRights(fds []int) control.SCMRightsVFS2 {
+	return &scmRights{fds}
+}
+
+// Files implements control.SCMRights.Files.
+func (c *scmRights) Files(ctx context.Context, max int) (control.RightsFilesVFS2, bool) {
+	n := max
+	var trunc bool
+	if l := len(c.fds); n > l {
+		n = l
+	} else if n < l {
+		trunc = true
+	}
+
+	rf := control.RightsFilesVFS2(fdsToFiles(ctx, c.fds[:n]))
+
+	// Only consume converted FDs (fdsToFiles may convert fewer than n FDs).
+	c.fds = c.fds[len(rf):]
+	return rf, trunc
+}
+
+// Clone implements transport.RightsControlMessage.Clone.
+func (c *scmRights) Clone() transport.RightsControlMessage {
+	// Host rights never need to be cloned.
+	return nil
+}
+
+// Release implements transport.RightsControlMessage.Release.
+func (c *scmRights) Release() {
+	for _, fd := range c.fds {
+		syscall.Close(fd)
+	}
+	c.fds = nil
+}
+
+// If an error is encountered, only files created before the error will be
+// returned. This is what Linux does.
+func fdsToFiles(ctx context.Context, fds []int) []*vfs.FileDescription {
+	files := make([]*vfs.FileDescription, 0, len(fds))
+	for _, fd := range fds {
+		// Get flags. We do it here because they may be modified
+		// by subsequent functions.
+		fileFlags, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_GETFL, 0)
+		if errno != 0 {
+			ctx.Warningf("Error retrieving host FD flags: %v", error(errno))
+			break
+		}
+
+		// Create the file backed by hostFD.
+		file, err := ImportFD(ctx, kernel.KernelFromContext(ctx).HostMount(), fd, false /* isTTY */)
+		if err != nil {
+			ctx.Warningf("Error creating file from host FD: %v", err)
+			break
+		}
+
+		if err := file.SetStatusFlags(ctx, auth.CredentialsFromContext(ctx), uint32(fileFlags&linux.O_NONBLOCK)); err != nil {
+			ctx.Warningf("Error setting flags on host FD file: %v", err)
+			break
+		}
+
+		files = append(files, file)
+	}
+	return files
+}

pkg/sentry/socket/control/BUILD

@@ -4,7 +4,10 @@ package(licenses = ["notice"])
 
 go_library(
     name = "control",
-    srcs = ["control.go"],
+    srcs = [
+        "control.go",
+        "control_vfs2.go",
+    ],
     imports = [
         "gvisor.dev/gvisor/pkg/sentry/fs",
     ],
@@ -18,6 +21,7 @@ go_library(
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/socket",
         "//pkg/sentry/socket/unix/transport",
+        "//pkg/sentry/vfs",
         "//pkg/syserror",
         "//pkg/tcpip",
         "//pkg/usermem",

pkg/sentry/socket/control/control.go

@@ -41,6 +41,8 @@ type SCMCredentials interface {
 	Credentials(t *kernel.Task) (kernel.ThreadID, auth.UID, auth.GID)
 }
 
+// LINT.IfChange
+
 // SCMRights represents a SCM_RIGHTS socket control message.
 type SCMRights interface {
 	transport.RightsControlMessage
@@ -142,6 +144,8 @@ func PackRights(t *kernel.Task, rights SCMRights, cloexec bool, buf []byte, flag
 	return putCmsg(buf, flags, linux.SCM_RIGHTS, align, fds)
 }
 
+// LINT.ThenChange(./control_vfs2.go)
+
 // scmCredentials represents an SCM_CREDENTIALS socket control message.
 //
 // +stateify savable
@@ -537,11 +541,19 @@ func Parse(t *kernel.Task, socketOrEndpoint interface{}, buf []byte) (socket.Con
 	}
 
 	if len(fds) > 0 {
-		rights, err := NewSCMRights(t, fds)
-		if err != nil {
-			return socket.ControlMessages{}, err
+		if kernel.VFS2Enabled {
+			rights, err := NewSCMRightsVFS2(t, fds)
+			if err != nil {
+				return socket.ControlMessages{}, err
+			}
+			cmsgs.Unix.Rights = rights
+		} else {
+			rights, err := NewSCMRights(t, fds)
+			if err != nil {
+				return socket.ControlMessages{}, err
+			}
+			cmsgs.Unix.Rights = rights
 		}
-		cmsgs.Unix.Rights = rights
 	}
 
 	return cmsgs, nil
@@ -566,6 +578,8 @@ func MakeCreds(t *kernel.Task) SCMCredentials {
 	return &scmCredentials{t, tcred.EffectiveKUID, tcred.EffectiveKGID}
 }
 
+// LINT.IfChange
+
 // New creates default control messages if needed.
 func New(t *kernel.Task, socketOrEndpoint interface{}, rights SCMRights) transport.ControlMessages {
 	return transport.ControlMessages{
@@ -573,3 +587,5 @@ func New(t *kernel.Task, socketOrEndpoint interface{}, rights SCMRights) transpo
 		Rights:      rights,
 	}
 }
+
+// LINT.ThenChange(./control_vfs2.go)

pkg/sentry/socket/control/control_vfs2.go

@@ -0,0 +1,131 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package control
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// SCMRightsVFS2 represents a SCM_RIGHTS socket control message.
+type SCMRightsVFS2 interface {
+	transport.RightsControlMessage
+
+	// Files returns up to max RightsFiles.
+	//
+	// Returned files are consumed and ownership is transferred to the caller.
+	// Subsequent calls to Files will return the next files.
+	Files(ctx context.Context, max int) (rf RightsFilesVFS2, truncated bool)
+}
+
+// RightsFiles represents a SCM_RIGHTS socket control message. A reference is
+// maintained for each vfs.FileDescription and is release either when an FD is created or
+// when the Release method is called.
+type RightsFilesVFS2 []*vfs.FileDescription
+
+// NewSCMRightsVFS2 creates a new SCM_RIGHTS socket control message
+// representation using local sentry FDs.
+func NewSCMRightsVFS2(t *kernel.Task, fds []int32) (SCMRightsVFS2, error) {
+	files := make(RightsFilesVFS2, 0, len(fds))
+	for _, fd := range fds {
+		file := t.GetFileVFS2(fd)
+		if file == nil {
+			files.Release()
+			return nil, syserror.EBADF
+		}
+		files = append(files, file)
+	}
+	return &files, nil
+}
+
+// Files implements SCMRights.Files.
+func (fs *RightsFilesVFS2) Files(ctx context.Context, max int) (RightsFilesVFS2, bool) {
+	n := max
+	var trunc bool
+	if l := len(*fs); n > l {
+		n = l
+	} else if n < l {
+		trunc = true
+	}
+	rf := (*fs)[:n]
+	*fs = (*fs)[n:]
+	return rf, trunc
+}
+
+// Clone implements transport.RightsControlMessage.Clone.
+func (fs *RightsFilesVFS2) Clone() transport.RightsControlMessage {
+	nfs := append(RightsFilesVFS2(nil), *fs...)
+	for _, nf := range nfs {
+		nf.IncRef()
+	}
+	return &nfs
+}
+
+// Release implements transport.RightsControlMessage.Release.
+func (fs *RightsFilesVFS2) Release() {
+	for _, f := range *fs {
+		f.DecRef()
+	}
+	*fs = nil
+}
+
+// rightsFDsVFS2 gets up to the specified maximum number of FDs.
+func rightsFDsVFS2(t *kernel.Task, rights SCMRightsVFS2, cloexec bool, max int) ([]int32, bool) {
+	files, trunc := rights.Files(t, max)
+	fds := make([]int32, 0, len(files))
+	for i := 0; i < max && len(files) > 0; i++ {
+		fd, err := t.NewFDFromVFS2(0, files[0], kernel.FDFlags{
+			CloseOnExec: cloexec,
+		})
+		files[0].DecRef()
+		files = files[1:]
+		if err != nil {
+			t.Warningf("Error inserting FD: %v", err)
+			// This is what Linux does.
+			break
+		}
+
+		fds = append(fds, int32(fd))
+	}
+	return fds, trunc
+}
+
+// PackRightsVFS2 packs as many FDs as will fit into the unused capacity of buf.
+func PackRightsVFS2(t *kernel.Task, rights SCMRightsVFS2, cloexec bool, buf []byte, flags int) ([]byte, int) {
+	maxFDs := (cap(buf) - len(buf) - linux.SizeOfControlMessageHeader) / 4
+	// Linux does not return any FDs if none fit.
+	if maxFDs <= 0 {
+		flags |= linux.MSG_CTRUNC
+		return buf, flags
+	}
+	fds, trunc := rightsFDsVFS2(t, rights, cloexec, maxFDs)
+	if trunc {
+		flags |= linux.MSG_CTRUNC
+	}
+	align := t.Arch().Width()
+	return putCmsg(buf, flags, linux.SCM_RIGHTS, align, fds)
+}
+
+// NewVFS2 creates default control messages if needed.
+func NewVFS2(t *kernel.Task, socketOrEndpoint interface{}, rights SCMRightsVFS2) transport.ControlMessages {
+	return transport.ControlMessages{
+		Credentials: makeCreds(t, socketOrEndpoint),
+		Rights:      rights,
+	}
+}

pkg/sentry/syscalls/linux/vfs2/socket.go

@@ -804,7 +804,7 @@ func recvSingleMsg(t *kernel.Task, s socket.SocketVFS2, msgPtr usermem.Addr, fla
 	}
 
 	if cms.Unix.Rights != nil {
-		controlData, mflags = control.PackRights(t, cms.Unix.Rights.(control.SCMRights), flags&linux.MSG_CMSG_CLOEXEC != 0, controlData, mflags)
+		controlData, mflags = control.PackRightsVFS2(t, cms.Unix.Rights.(control.SCMRightsVFS2), flags&linux.MSG_CMSG_CLOEXEC != 0, controlData, mflags)
 	}
 
 	// Copy the address to the caller.