Refactor fdimport.Import and read host fd flags before importing.

PiperOrigin-RevId: 558269013

pkg/sentry/fdimport/BUILD

@@ -18,5 +18,6 @@ go_library(
         "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/vfs",
+        "@org_golang_x_sys//unix:go_default_library",
     ],
 )

pkg/sentry/fdimport/fdimport.go

@@ -18,6 +18,7 @@ package fdimport
 import (
 	"fmt"
 
+	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fd"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/host"
@@ -30,27 +31,43 @@ import (
 // sets up TTY for sentry stdin, stdout, and stderr FDs. Used FDs are either
 // closed or released. It's safe for the caller to close any remaining files
 // upon return.
-func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth.KUID, gid auth.KGID, stdioFDs map[int]*fd.FD) (*host.TTYFileDescription, error) {
+func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth.KUID, gid auth.KGID, fds map[int]*fd.FD) (*host.TTYFileDescription, error) {
 	k := kernel.KernelFromContext(ctx)
 	if k == nil {
 		return nil, fmt.Errorf("cannot find kernel from context")
 	}
+	mnt := k.HostMount()
+
+	// Collect host fds and flags. Do this before importing any fds because
+	// multiple fds may refer to the same file, and importing fds may
+	// change flags.
+	fdFlags := make(map[*fd.FD]kernel.FDFlags)
+	for _, hostFD := range fds {
+		var err error
+		fdFlags[hostFD], err = getFDFlags(hostFD)
+		if err != nil {
+			return nil, err
+		}
+	}
 
 	var ttyFile *vfs.FileDescription
-	for appFD, hostFD := range stdioFDs {
+	for appFD, hostFD := range fds {
+		fdOpts := host.NewFDOptions{
+			Savable: true,
+		}
+		if uid != auth.NoID || gid != auth.NoID {
+			fdOpts.VirtualOwner = true
+			fdOpts.UID = uid
+			fdOpts.GID = gid
+		}
 		var appFile *vfs.FileDescription
 
 		if console && appFD < 3 {
 			// Import the file as a host TTY file.
 			if ttyFile == nil {
+				fdOpts.IsTTY = true
 				var err error
-				appFile, err = host.NewFD(ctx, k.HostMount(), hostFD.FD(), &host.NewFDOptions{
-					Savable:      true,
-					IsTTY:        true,
-					VirtualOwner: true,
-					UID:          uid,
-					GID:          gid,
-				})
+				appFile, err = host.NewFD(ctx, mnt, hostFD.FD(), &fdOpts)
 				if err != nil {
 					return nil, err
 				}
@@ -68,12 +85,7 @@ func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth
 			}
 		} else {
 			var err error
-			appFile, err = host.NewFD(ctx, k.HostMount(), hostFD.FD(), &host.NewFDOptions{
-				Savable:      true,
-				VirtualOwner: true,
-				UID:          uid,
-				GID:          gid,
-			})
+			appFile, err = host.NewFD(ctx, mnt, hostFD.FD(), &fdOpts)
 			if err != nil {
 				return nil, err
 			}
@@ -81,13 +93,22 @@ func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth
 			hostFD.Release() // FD is transfered to host FD.
 		}
 
-		if err := fdTable.NewFDAt(ctx, int32(appFD), appFile, kernel.FDFlags{}); err != nil {
+		if err := fdTable.NewFDAt(ctx, int32(appFD), appFile, fdFlags[hostFD]); err != nil {
 			return nil, err
 		}
 	}
-
 	if ttyFile == nil {
 		return nil, nil
 	}
 	return ttyFile.Impl().(*host.TTYFileDescription), nil
 }
+
+func getFDFlags(f *fd.FD) (kernel.FDFlags, error) {
+	fdflags, _, errno := unix.Syscall(unix.SYS_FCNTL, uintptr(f.FD()), unix.F_GETFD, 0)
+	if errno != 0 {
+		return kernel.FDFlags{}, fmt.Errorf("failed to get fd flags for fd %d (errno=%d)", f, errno)
+	}
+	return kernel.FDFlags{
+		CloseOnExec: fdflags&unix.O_CLOEXEC != 0,
+	}, nil
+}