Add FileExec flag to OpenOptions

This allow callers to say whether the file is being
opened to be executed, so that the proper checks can
be done from FilesystemImpl.OpenAt()

Updates #1623

PiperOrigin-RevId: 295042595

pkg/sentry/fsimpl/ext/filesystem.go

@@ -296,7 +296,7 @@ func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 	if vfs.MayWriteFileWithOpenFlags(opts.Flags) || opts.Flags&(linux.O_CREAT|linux.O_EXCL|linux.O_TMPFILE) != 0 {
 		return nil, syserror.EROFS
 	}
-	return inode.open(rp, vfsd, opts.Flags)
+	return inode.open(rp, vfsd, &opts)
 }
 
 // ReadlinkAt implements vfs.FilesystemImpl.ReadlinkAt.

pkg/sentry/fsimpl/ext/inode.go

@@ -148,8 +148,8 @@ func newInode(fs *filesystem, inodeNum uint32) (*inode, error) {
 }
 
 // open creates and returns a file description for the dentry passed in.
-func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
-	ats := vfs.AccessTypesForOpenFlags(flags)
+func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts *vfs.OpenOptions) (*vfs.FileDescription, error) {
+	ats := vfs.AccessTypesForOpenFlags(opts)
 	if err := in.checkPermissions(rp.Credentials(), ats); err != nil {
 		return nil, err
 	}
@@ -157,7 +157,7 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*v
 	switch in.impl.(type) {
 	case *regularFile:
 		var fd regularFileFD
-		if err := fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{}); err != nil {
+		if err := fd.vfsfd.Init(&fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{}); err != nil {
 			return nil, err
 		}
 		return &fd.vfsfd, nil
@@ -168,17 +168,17 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*v
 			return nil, syserror.EISDIR
 		}
 		var fd directoryFD
-		if err := fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{}); err != nil {
+		if err := fd.vfsfd.Init(&fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{}); err != nil {
 			return nil, err
 		}
 		return &fd.vfsfd, nil
 	case *symlink:
-		if flags&linux.O_PATH == 0 {
+		if opts.Flags&linux.O_PATH == 0 {
 			// Can't open symlinks without O_PATH.
 			return nil, syserror.ELOOP
 		}
 		var fd symlinkFD
-		fd.vfsfd.Init(&fd, flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
+		fd.vfsfd.Init(&fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
 		return &fd.vfsfd, nil
 	default:
 		panic(fmt.Sprintf("unknown inode type: %T", in.impl))

pkg/sentry/fsimpl/gofer/filesystem.go

@@ -593,7 +593,7 @@ func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 		}
 	}
 	if rp.Done() {
-		return start.openLocked(ctx, rp, opts.Flags)
+		return start.openLocked(ctx, rp, &opts)
 	}
 
 afterTrailingSymlink:
@@ -633,12 +633,12 @@ afterTrailingSymlink:
 		start = parent
 		goto afterTrailingSymlink
 	}
-	return child.openLocked(ctx, rp, opts.Flags)
+	return child.openLocked(ctx, rp, &opts)
 }
 
 // Preconditions: fs.renameMu must be locked.
-func (d *dentry) openLocked(ctx context.Context, rp *vfs.ResolvingPath, flags uint32) (*vfs.FileDescription, error) {
-	ats := vfs.AccessTypesForOpenFlags(flags)
+func (d *dentry) openLocked(ctx context.Context, rp *vfs.ResolvingPath, opts *vfs.OpenOptions) (*vfs.FileDescription, error) {
+	ats := vfs.AccessTypesForOpenFlags(opts)
 	if err := d.checkPermissions(rp.Credentials(), ats, d.isDir()); err != nil {
 		return nil, err
 	}
@@ -646,11 +646,11 @@ func (d *dentry) openLocked(ctx context.Context, rp *vfs.ResolvingPath, flags ui
 	filetype := d.fileType()
 	switch {
 	case filetype == linux.S_IFREG && !d.fs.opts.regularFilesUseSpecialFileFD:
-		if err := d.ensureSharedHandle(ctx, ats&vfs.MayRead != 0, ats&vfs.MayWrite != 0, flags&linux.O_TRUNC != 0); err != nil {
+		if err := d.ensureSharedHandle(ctx, ats&vfs.MayRead != 0, ats&vfs.MayWrite != 0, opts.Flags&linux.O_TRUNC != 0); err != nil {
 			return nil, err
 		}
 		fd := &regularFileFD{}
-		if err := fd.vfsfd.Init(fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{
+		if err := fd.vfsfd.Init(fd, opts.Flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{
 			AllowDirectIO: true,
 		}); err != nil {
 			return nil, err
@@ -658,21 +658,21 @@ func (d *dentry) openLocked(ctx context.Context, rp *vfs.ResolvingPath, flags ui
 		return &fd.vfsfd, nil
 	case filetype == linux.S_IFDIR:
 		// Can't open directories with O_CREAT.
-		if flags&linux.O_CREAT != 0 {
+		if opts.Flags&linux.O_CREAT != 0 {
 			return nil, syserror.EISDIR
 		}
 		// Can't open directories writably.
 		if ats&vfs.MayWrite != 0 {
 			return nil, syserror.EISDIR
 		}
-		if flags&linux.O_DIRECT != 0 {
+		if opts.Flags&linux.O_DIRECT != 0 {
 			return nil, syserror.EINVAL
 		}
 		if err := d.ensureSharedHandle(ctx, ats&vfs.MayRead != 0, false /* write */, false /* trunc */); err != nil {
 			return nil, err
 		}
 		fd := &directoryFD{}
-		if err := fd.vfsfd.Init(fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{}); err != nil {
+		if err := fd.vfsfd.Init(fd, opts.Flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{}); err != nil {
 			return nil, err
 		}
 		return &fd.vfsfd, nil
@@ -680,17 +680,17 @@ func (d *dentry) openLocked(ctx context.Context, rp *vfs.ResolvingPath, flags ui
 		// Can't open symlinks without O_PATH (which is unimplemented).
 		return nil, syserror.ELOOP
 	default:
-		if flags&linux.O_DIRECT != 0 {
+		if opts.Flags&linux.O_DIRECT != 0 {
 			return nil, syserror.EINVAL
 		}
-		h, err := openHandle(ctx, d.file, ats&vfs.MayRead != 0, ats&vfs.MayWrite != 0, flags&linux.O_TRUNC != 0)
+		h, err := openHandle(ctx, d.file, ats&vfs.MayRead != 0, ats&vfs.MayWrite != 0, opts.Flags&linux.O_TRUNC != 0)
 		if err != nil {
 			return nil, err
 		}
 		fd := &specialFileFD{
 			handle: h,
 		}
-		if err := fd.vfsfd.Init(fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{}); err != nil {
+		if err := fd.vfsfd.Init(fd, opts.Flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{}); err != nil {
 			h.close(ctx)
 			return nil, err
 		}

pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go

@@ -53,9 +53,9 @@ func (f *DynamicBytesFile) Init(creds *auth.Credentials, ino uint64, data vfs.Dy
 }
 
 // Open implements Inode.Open.
-func (f *DynamicBytesFile) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (f *DynamicBytesFile) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &DynamicBytesFD{}
-	if err := fd.Init(rp.Mount(), vfsd, f.data, flags); err != nil {
+	if err := fd.Init(rp.Mount(), vfsd, f.data, opts.Flags); err != nil {
 		return nil, err
 	}
 	return &fd.vfsfd, nil

pkg/sentry/fsimpl/kernfs/fd_impl_util.go

@@ -43,12 +43,12 @@ type GenericDirectoryFD struct {
 }
 
 // Init initializes a GenericDirectoryFD.
-func (fd *GenericDirectoryFD) Init(m *vfs.Mount, d *vfs.Dentry, children *OrderedChildren, flags uint32) error {
-	if vfs.AccessTypesForOpenFlags(flags)&vfs.MayWrite != 0 {
+func (fd *GenericDirectoryFD) Init(m *vfs.Mount, d *vfs.Dentry, children *OrderedChildren, opts *vfs.OpenOptions) error {
+	if vfs.AccessTypesForOpenFlags(opts)&vfs.MayWrite != 0 {
 		// Can't open directories for writing.
 		return syserror.EISDIR
 	}
-	if err := fd.vfsfd.Init(fd, flags, m, d, &vfs.FileDescriptionOptions{}); err != nil {
+	if err := fd.vfsfd.Init(fd, opts.Flags, m, d, &vfs.FileDescriptionOptions{}); err != nil {
 		return err
 	}
 	fd.children = children

pkg/sentry/fsimpl/kernfs/filesystem.go

@@ -365,7 +365,7 @@ func (fs *Filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 	// appropriate bits in rp), but are returned by
 	// FileDescriptionImpl.StatusFlags().
 	opts.Flags &= linux.O_ACCMODE | linux.O_CREAT | linux.O_EXCL | linux.O_TRUNC | linux.O_DIRECTORY | linux.O_NOFOLLOW
-	ats := vfs.AccessTypesForOpenFlags(opts.Flags)
+	ats := vfs.AccessTypesForOpenFlags(&opts)
 
 	// Do not create new file.
 	if opts.Flags&linux.O_CREAT == 0 {
@@ -379,7 +379,7 @@ func (fs *Filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 		if err := inode.CheckPermissions(ctx, rp.Credentials(), ats); err != nil {
 			return nil, err
 		}
-		return inode.Open(rp, vfsd, opts.Flags)
+		return inode.Open(rp, vfsd, opts)
 	}
 
 	// May create new file.
@@ -398,7 +398,7 @@ func (fs *Filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 		if err := inode.CheckPermissions(ctx, rp.Credentials(), ats); err != nil {
 			return nil, err
 		}
-		return inode.Open(rp, vfsd, opts.Flags)
+		return inode.Open(rp, vfsd, opts)
 	}
 afterTrailingSymlink:
 	parentVFSD, parentInode, err := fs.walkParentDirLocked(ctx, rp)
@@ -438,7 +438,7 @@ afterTrailingSymlink:
 			return nil, err
 		}
 		parentVFSD.Impl().(*Dentry).InsertChild(pc, child)
-		return child.Impl().(*Dentry).inode.Open(rp, child, opts.Flags)
+		return child.Impl().(*Dentry).inode.Open(rp, child, opts)
 	}
 	// Open existing file or follow symlink.
 	if mustCreate {
@@ -463,7 +463,7 @@ afterTrailingSymlink:
 	if err := childInode.CheckPermissions(ctx, rp.Credentials(), ats); err != nil {
 		return nil, err
 	}
-	return childInode.Open(rp, childVFSD, opts.Flags)
+	return childInode.Open(rp, childVFSD, opts)
 }
 
 // ReadlinkAt implements vfs.FilesystemImpl.ReadlinkAt.

pkg/sentry/fsimpl/kernfs/inode_impl_util.go

@@ -507,7 +507,7 @@ type InodeSymlink struct {
 }
 
 // Open implements Inode.Open.
-func (InodeSymlink) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (InodeSymlink) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	return nil, syserror.ELOOP
 }
 
@@ -549,8 +549,8 @@ func (s *StaticDirectory) Init(creds *auth.Credentials, ino uint64, perm linux.F
 }
 
 // Open implements kernfs.Inode.
-func (s *StaticDirectory) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (s *StaticDirectory) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &s.OrderedChildren, flags)
+	fd.Init(rp.Mount(), vfsd, &s.OrderedChildren, &opts)
 	return fd.VFSFileDescription(), nil
 }

pkg/sentry/fsimpl/kernfs/kernfs.go

@@ -303,7 +303,7 @@ type Inode interface {
 	// inode for its lifetime.
 	//
 	// Precondition: !rp.Done(). vfsd.Impl() must be a kernfs Dentry.
-	Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error)
+	Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error)
 }
 
 type inodeRefs interface {

pkg/sentry/fsimpl/kernfs/kernfs_test.go

@@ -113,9 +113,9 @@ func (fs *filesystem) newReadonlyDir(creds *auth.Credentials, mode linux.FileMod
 	return &dir.dentry
 }
 
-func (d *readonlyDir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (d *readonlyDir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &kernfs.GenericDirectoryFD{}
-	if err := fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, flags); err != nil {
+	if err := fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, &opts); err != nil {
 		return nil, err
 	}
 	return fd.VFSFileDescription(), nil
@@ -143,9 +143,9 @@ func (fs *filesystem) newDir(creds *auth.Credentials, mode linux.FileMode, conte
 	return &dir.dentry
 }
 
-func (d *dir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (d *dir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &kernfs.GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, flags)
+	fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
 	return fd.VFSFileDescription(), nil
 }
 

pkg/sentry/fsimpl/proc/subtasks.go

@@ -114,9 +114,9 @@ func (i *subtasksInode) IterDirents(ctx context.Context, cb vfs.IterDirentsCallb
 }
 
 // Open implements kernfs.Inode.
-func (i *subtasksInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (i *subtasksInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &kernfs.GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, flags)
+	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
 	return fd.VFSFileDescription(), nil
 }
 

pkg/sentry/fsimpl/proc/task.go

@@ -98,9 +98,9 @@ func (i *taskInode) Valid(ctx context.Context) bool {
 }
 
 // Open implements kernfs.Inode.
-func (i *taskInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (i *taskInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &kernfs.GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, flags)
+	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
 	return fd.VFSFileDescription(), nil
 }
 

pkg/sentry/fsimpl/proc/tasks.go

@@ -205,9 +205,9 @@ func (i *tasksInode) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback
 }
 
 // Open implements kernfs.Inode.
-func (i *tasksInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (i *tasksInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &kernfs.GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, flags)
+	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
 	return fd.VFSFileDescription(), nil
 }
 

pkg/sentry/fsimpl/sys/sys.go

@@ -97,9 +97,9 @@ func (d *dir) SetStat(fs *vfs.Filesystem, opts vfs.SetStatOptions) error {
 }
 
 // Open implements kernfs.Inode.Open.
-func (d *dir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
+func (d *dir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	fd := &kernfs.GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, flags)
+	fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
 	return fd.VFSFileDescription(), nil
 }
 

pkg/sentry/fsimpl/tmpfs/filesystem.go

@@ -334,7 +334,7 @@ afterTrailingSymlink:
 }
 
 func (d *dentry) open(ctx context.Context, rp *vfs.ResolvingPath, opts *vfs.OpenOptions, afterCreate bool) (*vfs.FileDescription, error) {
-	ats := vfs.AccessTypesForOpenFlags(opts.Flags)
+	ats := vfs.AccessTypesForOpenFlags(opts)
 	if !afterCreate {
 		if err := d.inode.checkPermissions(rp.Credentials(), ats, d.inode.isDir()); err != nil {
 			return nil, err

pkg/sentry/vfs/options.go

@@ -72,6 +72,11 @@ type OpenOptions struct {
 	// If FilesystemImpl.OpenAt() creates a file, Mode is the file mode for the
 	// created file.
 	Mode linux.FileMode
+
+	// FileExec is set when the file is being opened to be executed.
+	// VirtualFilesystem.OpenAt() checks that the caller has execute permissions
+	// on the file, and that the file is a regular file.
+	FileExec bool
 }
 
 // ReadOptions contains options to FileDescription.PRead(),

pkg/sentry/vfs/permissions.go

@@ -103,17 +103,22 @@ func GenericCheckPermissions(creds *auth.Credentials, ats AccessTypes, isDir boo
 // AccessTypesForOpenFlags returns MayRead|MayWrite in this case.
 //
 // Use May{Read,Write}FileWithOpenFlags() for these checks instead.
-func AccessTypesForOpenFlags(flags uint32) AccessTypes {
-	switch flags & linux.O_ACCMODE {
+func AccessTypesForOpenFlags(opts *OpenOptions) AccessTypes {
+	ats := AccessTypes(0)
+	if opts.FileExec {
+		ats |= MayExec
+	}
+
+	switch opts.Flags & linux.O_ACCMODE {
 	case linux.O_RDONLY:
-		if flags&linux.O_TRUNC != 0 {
-			return MayRead | MayWrite
+		if opts.Flags&linux.O_TRUNC != 0 {
+			return ats | MayRead | MayWrite
 		}
-		return MayRead
+		return ats | MayRead
 	case linux.O_WRONLY:
-		return MayWrite
+		return ats | MayWrite
 	default:
-		return MayRead | MayWrite
+		return ats | MayRead | MayWrite
 	}
 }
 

pkg/sentry/vfs/vfs.go

@@ -379,6 +379,25 @@ func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credential
 		fd, err := rp.mount.fs.impl.OpenAt(ctx, rp, *opts)
 		if err == nil {
 			vfs.putResolvingPath(rp)
+
+			// TODO(gvisor.dev/issue/1193): Move inside fsimpl to avoid another call
+			// to FileDescription.Stat().
+			if opts.FileExec {
+				// Only a regular file can be executed.
+				stat, err := fd.Stat(ctx, StatOptions{Mask: linux.STATX_TYPE})
+				if err != nil {
+					return nil, err
+				}
+				if stat.Mask&linux.STATX_TYPE != 0 {
+					// This shouldn't happen, but if type can't be retrieved, file can't
+					// be executed.
+					return nil, syserror.EACCES
+				}
+				if linux.FileMode(stat.Mode).FileType() != linux.ModeRegular {
+					return nil, syserror.EACCES
+				}
+			}
+
 			return fd, nil
 		}
 		if !rp.handleError(err) {