Add lost changes to --pass-fd merge

GitHub pull request #8634 concluded that commit d1f3b45 should be
merged. However, the changes since commit feb40ac got lost in merge
36793c0. This commit is the lost diff.

runsc/cmd/boot.go

@@ -171,7 +171,7 @@ func (b *Boot) SetFlags(f *flag.FlagSet) {
 	f.IntVar(&b.deviceFD, "device-fd", -1, "FD for the platform device file")
 	f.Var(&b.ioFDs, "io-fds", "list of FDs to connect gofer clients. They must follow this order: root first, then mounts as defined in the spec")
 	f.Var(&b.stdioFDs, "stdio-fds", "list of FDs containing sandbox stdin, stdout, and stderr in that order")
-	f.Var(&b.passFDs, "custom-fds", "mapping of host to guest FDs. They must be in M:N format. M is the host and N the guest descriptor.")
+	f.Var(&b.passFDs, "pass-fd", "mapping of host to guest FDs. They must be in M:N format. M is the host and N the guest descriptor.")
 	f.Var(&b.overlayFilestoreFDs, "overlay-filestore-fds", "FDs to the regular files that will back the tmpfs upper mount in the overlay mounts.")
 	f.IntVar(&b.userLogFD, "user-log-fd", 0, "file descriptor to write user logs to. 0 means no logging.")
 	f.IntVar(&b.startSyncFD, "start-sync-fd", -1, "required FD to used to synchronize sandbox startup")

runsc/cmd/exec.go

@@ -60,7 +60,7 @@ type Exec struct {
 
 	// passFDs are user-supplied FDs from the host to be exposed to the
 	// sandboxed app.
-	passFDs intFlags
+	passFDs fdMappings
 }
 
 // Name implements subcommands.Command.Name.
@@ -104,7 +104,7 @@ func (ex *Exec) SetFlags(f *flag.FlagSet) {
 	f.StringVar(&ex.pidFile, "pid-file", "", "filename that the container pid will be written to")
 	f.StringVar(&ex.internalPidFile, "internal-pid-file", "", "filename that the container-internal pid will be written to")
 	f.StringVar(&ex.consoleSocket, "console-socket", "", "path to an AF_UNIX socket which will receive a file descriptor referencing the master end of the console's pseudoterminal")
-	f.Var(&ex.passFDs, "pass-fd", "file descriptors passed to the container. Can be supplied multiple times.")
+	f.Var(&ex.passFDs, "pass-fd", "file descriptor passed to the container in M:N format, where M is the host and N is the guest descriptor (can be supplied multiple times)")
 }
 
 // Execute implements subcommands.Command.Execute. It starts a process in an
@@ -152,18 +152,17 @@ func (ex *Exec) Execute(_ context.Context, f *flag.FlagSet, args ...any) subcomm
 	}
 
 	// Add custom file descriptors to the map.
-	var files []*os.File
-	for _, fd := range ex.passFDs {
-		file := os.NewFile(uintptr(fd), "")
+	for _, mapping := range ex.passFDs {
+		file := os.NewFile(uintptr(mapping.Host), "")
 		if file == nil {
-			util.Fatalf("failed to create file from file descriptor %d", fd)
+			util.Fatalf("failed to create file from file descriptor %d", mapping.Host)
 		}
-		fdMap[int(file.Fd())] = file
+		fdMap[mapping.Guest] = file
 	}
 
 	// Close the underlying file descriptors after we have passed them.
 	defer func() {
-		for _, file := range files {
+		for _, file := range fdMap {
 			fd := file.Fd()
 			if file.Close() != nil {
 				log.Debugf("Failed to close FD %d", fd)

runsc/cmd/fd_mapping.go

@@ -45,7 +45,19 @@ func (i *fdMappings) GetArray() []boot.FDMapping {
 func (i *fdMappings) Set(s string) error {
 	split := strings.Split(s, ":")
 	if len(split) != 2 {
-		return fmt.Errorf("invalid flag value: must be of format M:N")
+		// Split returns a slice of length 1 if its first argument does not
+		// contain the separator. An additional length check is not necessary.
+		// In case no separator is used and the argument is a valid integer, we
+		// assume that host FD and guest FD should be identical.
+		fd, err := strconv.Atoi(split[0])
+		if err != nil {
+			return fmt.Errorf("invalid flag value: must be an integer or a mapping of format M:N")
+		}
+		*i = append(*i, boot.FDMapping{
+			Host:  fd,
+			Guest: fd,
+		})
+		return nil
 	}
 
 	fdHost, err := strconv.Atoi(split[0])

runsc/cmd/run.go

@@ -38,7 +38,7 @@ type Run struct {
 
 	// passFDs are user-supplied FDs from the host to be exposed to the
 	// sandboxed app.
-	passFDs intFlags
+	passFDs fdMappings
 }
 
 // Name implements subcommands.Command.Name.
@@ -60,7 +60,7 @@ func (*Run) Usage() string {
 // SetFlags implements subcommands.Command.SetFlags.
 func (r *Run) SetFlags(f *flag.FlagSet) {
 	f.BoolVar(&r.detach, "detach", false, "detach from the container's process")
-	f.Var(&r.passFDs, "pass-fd", "file descriptors passed to the container. Can be supplied multiple times.")
+	f.Var(&r.passFDs, "pass-fd", "file descriptor passed to the container in M:N format, where M is the host and N is the guest descriptor (can be supplied multiple times)")
 	r.Create.SetFlags(f)
 }
 
@@ -98,12 +98,12 @@ func (r *Run) Execute(_ context.Context, f *flag.FlagSet, args ...any) subcomman
 
 	// Create files from file descriptors.
 	fdMap := make(map[int]*os.File)
-	for _, fd := range r.passFDs {
-		file := os.NewFile(uintptr(fd), "")
+	for _, mapping := range r.passFDs {
+		file := os.NewFile(uintptr(mapping.Host), "")
 		if file == nil {
-			return util.Errorf("Failed to create file from file descriptor %d", fd)
+			return util.Errorf("Failed to create file from file descriptor %d", mapping.Host)
 		}
-		fdMap[fd] = file
+		fdMap[mapping.Guest] = file
 	}
 
 	// Close the underlying file descriptors after we have passed them.

runsc/donation/donation.go

@@ -110,7 +110,7 @@ func (f *Agency) Transfer(cmd *exec.Cmd, nextFD int) int {
 // host to the sandbox. Making use of the agency is not necessary,
 func DonateAndTransferCustomFiles(cmd *exec.Cmd, nextFD int, files map[int]*os.File) int {
 	for fd, file := range files {
-		cmd.Args = append(cmd.Args, fmt.Sprintf("--custom-fds=%d:%d", nextFD, fd))
+		cmd.Args = append(cmd.Args, fmt.Sprintf("--pass-fd=%d:%d", nextFD, fd))
 		cmd.ExtraFiles = append(cmd.ExtraFiles, file)
 		nextFD++
 	}