Combine file mode and isDir arguments

Updates #1035

PiperOrigin-RevId: 303021328

12 files changed, 56 insertions, 61 deletions

diff --git a/pkg/abi/linux/file.go b/pkg/abi/linux/file.go
index dbe58acbe..055ac1d7c 100644
--- a/pkg/abi/linux/file.go
+++ b/pkg/abi/linux/file.go
@@ -287,6 +287,11 @@ func (m FileMode) ExtraBits() FileMode {
 	return m &^ (PermissionsMask | FileTypeMask)
 }
 
+// IsDir returns true if file type represents a directory.
+func (m FileMode) IsDir() bool {
+	return m.FileType() == S_IFDIR
+}
+
 // String returns a string representation of m.
 func (m FileMode) String() string {
 	var s []string
diff --git a/pkg/sentry/fsimpl/ext/inode.go b/pkg/sentry/fsimpl/ext/inode.go
index 6962083f5..a39a37318 100644
--- a/pkg/sentry/fsimpl/ext/inode.go
+++ b/pkg/sentry/fsimpl/ext/inode.go
@@ -186,7 +186,7 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts *vfs.OpenOpt
 }
 
 func (in *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
-	return vfs.GenericCheckPermissions(creds, ats, in.isDir(), uint16(in.diskInode.Mode()), in.diskInode.UID(), in.diskInode.GID())
+	return vfs.GenericCheckPermissions(creds, ats, in.diskInode.Mode(), in.diskInode.UID(), in.diskInode.GID())
 }
 
 // statTo writes the statx fields to the output parameter.
diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 26b492185..1e43df9ec 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -119,7 +119,7 @@ func (fs *filesystem) stepLocked(ctx context.Context, rp *vfs.ResolvingPath, d *
 	if !d.isDir() {
 		return nil, syserror.ENOTDIR
 	}
-	if err := d.checkPermissions(rp.Credentials(), vfs.MayExec, true); err != nil {
+	if err := d.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil {
 		return nil, err
 	}
 afterSymlink:
@@ -314,7 +314,7 @@ func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, dir
 	if err != nil {
 		return err
 	}
-	if err := parent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true); err != nil {
+	if err := parent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	if parent.isDeleted() {
@@ -378,7 +378,7 @@ func (fs *filesystem) unlinkAt(ctx context.Context, rp *vfs.ResolvingPath, dir b
 	if err != nil {
 		return err
 	}
-	if err := parent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true); err != nil {
+	if err := parent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	if err := rp.Mount().CheckBeginWrite(); err != nil {
@@ -512,7 +512,7 @@ func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds
 	if err != nil {
 		return err
 	}
-	return d.checkPermissions(creds, ats, d.isDir())
+	return d.checkPermissions(creds, ats)
 }
 
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
@@ -528,7 +528,7 @@ func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, op
 		if !d.isDir() {
 			return nil, syserror.ENOTDIR
 		}
-		if err := d.checkPermissions(rp.Credentials(), vfs.MayExec, true); err != nil {
+		if err := d.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil {
 			return nil, err
 		}
 	}
@@ -624,7 +624,7 @@ afterTrailingSymlink:
 		return nil, err
 	}
 	// Check for search permission in the parent directory.
-	if err := parent.checkPermissions(rp.Credentials(), vfs.MayExec, true); err != nil {
+	if err := parent.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil {
 		return nil, err
 	}
 	// Determine whether or not we need to create a file.
@@ -661,7 +661,7 @@ afterTrailingSymlink:
 // Preconditions: fs.renameMu must be locked.
 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 {
+	if err := d.checkPermissions(rp.Credentials(), ats); err != nil {
 		return nil, err
 	}
 	mnt := rp.Mount()
@@ -722,7 +722,7 @@ func (d *dentry) openLocked(ctx context.Context, rp *vfs.ResolvingPath, opts *vf
 
 // Preconditions: d.fs.renameMu must be locked. d.dirMu must be locked.
 func (d *dentry) createAndOpenChildLocked(ctx context.Context, rp *vfs.ResolvingPath, opts *vfs.OpenOptions) (*vfs.FileDescription, error) {
-	if err := d.checkPermissions(rp.Credentials(), vfs.MayWrite, true); err != nil {
+	if err := d.checkPermissions(rp.Credentials(), vfs.MayWrite); err != nil {
 		return nil, err
 	}
 	if d.isDeleted() {
@@ -884,7 +884,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 			return err
 		}
 	}
-	if err := oldParent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true); err != nil {
+	if err := oldParent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	vfsObj := rp.VirtualFilesystem()
@@ -904,7 +904,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 			return syserror.EINVAL
 		}
 		if oldParent != newParent {
-			if err := renamed.checkPermissions(rp.Credentials(), vfs.MayWrite, true); err != nil {
+			if err := renamed.checkPermissions(rp.Credentials(), vfs.MayWrite); err != nil {
 				return err
 			}
 		}
@@ -915,7 +915,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 	}
 
 	if oldParent != newParent {
-		if err := newParent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true); err != nil {
+		if err := newParent.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 			return err
 		}
 		newParent.dirMu.Lock()
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 13928ce36..cf276a417 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -721,7 +721,8 @@ func (d *dentry) setStat(ctx context.Context, creds *auth.Credentials, stat *lin
 	if stat.Mask&^(linux.STATX_MODE|linux.STATX_UID|linux.STATX_GID|linux.STATX_ATIME|linux.STATX_MTIME|linux.STATX_SIZE) != 0 {
 		return syserror.EPERM
 	}
-	if err := vfs.CheckSetStat(ctx, creds, stat, uint16(atomic.LoadUint32(&d.mode))&^linux.S_IFMT, auth.KUID(atomic.LoadUint32(&d.uid)), auth.KGID(atomic.LoadUint32(&d.gid))); err != nil {
+	mode := linux.FileMode(atomic.LoadUint32(&d.mode))
+	if err := vfs.CheckSetStat(ctx, creds, stat, mode, auth.KUID(atomic.LoadUint32(&d.uid)), auth.KGID(atomic.LoadUint32(&d.gid))); err != nil {
 		return err
 	}
 	if err := mnt.CheckBeginWrite(); err != nil {
@@ -843,8 +844,8 @@ func (d *dentry) setStat(ctx context.Context, creds *auth.Credentials, stat *lin
 	return nil
 }
 
-func (d *dentry) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes, isDir bool) error {
-	return vfs.GenericCheckPermissions(creds, ats, isDir, uint16(atomic.LoadUint32(&d.mode))&0777, auth.KUID(atomic.LoadUint32(&d.uid)), auth.KGID(atomic.LoadUint32(&d.gid)))
+func (d *dentry) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
+	return vfs.GenericCheckPermissions(creds, ats, linux.FileMode(atomic.LoadUint32(&d.mode)), auth.KUID(atomic.LoadUint32(&d.uid)), auth.KGID(atomic.LoadUint32(&d.gid)))
 }
 
 // IncRef implements vfs.DentryImpl.IncRef.
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index 1f735628f..a54985ef5 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -167,8 +167,8 @@ func fileFlagsFromHostFD(fd int) (int, error) {
 }
 
 // CheckPermissions implements kernfs.Inode.
-func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, atx vfs.AccessTypes) error {
-	return vfs.GenericCheckPermissions(creds, atx, false /* isDir */, uint16(i.mode), i.uid, i.gid)
+func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	return vfs.GenericCheckPermissions(creds, ats, i.mode, i.uid, i.gid)
 }
 
 // Mode implements kernfs.Inode.
@@ -306,7 +306,7 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 	if m&^(linux.STATX_MODE|linux.STATX_SIZE|linux.STATX_ATIME|linux.STATX_MTIME) != 0 {
 		return syserror.EPERM
 	}
-	if err := vfs.CheckSetStat(ctx, creds, &s, uint16(i.Mode().Permissions()), i.uid, i.gid); err != nil {
+	if err := vfs.CheckSetStat(ctx, creds, &s, i.Mode(), i.uid, i.gid); err != nil {
 		return err
 	}
 
diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
index 75c4bab1a..bfa786c88 100644
--- a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
@@ -206,8 +206,7 @@ func (fd *GenericDirectoryFD) Stat(ctx context.Context, opts vfs.StatOptions) (l
 
 // SetStat implements vfs.FileDescriptionImpl.SetStat.
 func (fd *GenericDirectoryFD) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
-	fs := fd.filesystem()
 	creds := auth.CredentialsFromContext(ctx)
 	inode := fd.vfsfd.VirtualDentry().Dentry().Impl().(*Dentry).inode
-	return inode.SetStat(ctx, fs, creds, opts)
+	return inode.SetStat(ctx, fd.filesystem(), creds, opts)
 }
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index c612dcf07..5c84b10c9 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -241,7 +241,7 @@ func (a *InodeAttrs) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *aut
 	if opts.Stat.Mask&^(linux.STATX_MODE|linux.STATX_UID|linux.STATX_GID) != 0 {
 		return syserror.EPERM
 	}
-	if err := vfs.CheckSetStat(ctx, creds, &opts.Stat, uint16(a.Mode().Permissions()), auth.KUID(atomic.LoadUint32(&a.uid)), auth.KGID(atomic.LoadUint32(&a.gid))); err != nil {
+	if err := vfs.CheckSetStat(ctx, creds, &opts.Stat, a.Mode(), auth.KUID(atomic.LoadUint32(&a.uid)), auth.KGID(atomic.LoadUint32(&a.gid))); err != nil {
 		return err
 	}
 
@@ -273,12 +273,10 @@ func (a *InodeAttrs) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *aut
 
 // CheckPermissions implements Inode.CheckPermissions.
 func (a *InodeAttrs) CheckPermissions(_ context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
-	mode := a.Mode()
 	return vfs.GenericCheckPermissions(
 		creds,
 		ats,
-		mode.FileType() == linux.ModeDirectory,
-		uint16(mode),
+		a.Mode(),
 		auth.KUID(atomic.LoadUint32(&a.uid)),
 		auth.KGID(atomic.LoadUint32(&a.gid)),
 	)
diff --git a/pkg/sentry/fsimpl/proc/task.go b/pkg/sentry/fsimpl/proc/task.go
index 49d6efb0e..aee2a4392 100644
--- a/pkg/sentry/fsimpl/proc/task.go
+++ b/pkg/sentry/fsimpl/proc/task.go
@@ -172,14 +172,7 @@ func (i *taskOwnedInode) Stat(fs *vfs.Filesystem, opts vfs.StatOptions) (linux.S
 func (i *taskOwnedInode) CheckPermissions(_ context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
 	mode := i.Mode()
 	uid, gid := i.getOwner(mode)
-	return vfs.GenericCheckPermissions(
-		creds,
-		ats,
-		mode.FileType() == linux.ModeDirectory,
-		uint16(mode),
-		uid,
-		gid,
-	)
+	return vfs.GenericCheckPermissions(creds, ats, mode, uid, gid)
 }
 
 func (i *taskOwnedInode) getOwner(mode linux.FileMode) (auth.KUID, auth.KGID) {
diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index 75d01b853..12cc64385 100644
--- a/pkg/sentry/fsimpl/tmpfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
@@ -41,7 +41,7 @@ func stepLocked(rp *vfs.ResolvingPath, d *dentry) (*dentry, error) {
 	if !d.inode.isDir() {
 		return nil, syserror.ENOTDIR
 	}
-	if err := d.inode.checkPermissions(rp.Credentials(), vfs.MayExec, true); err != nil {
+	if err := d.inode.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil {
 		return nil, err
 	}
 afterSymlink:
@@ -125,7 +125,7 @@ func (fs *filesystem) doCreateAt(rp *vfs.ResolvingPath, dir bool, create func(pa
 	if err != nil {
 		return err
 	}
-	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true /* isDir */); err != nil {
+	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	name := rp.Component()
@@ -163,7 +163,7 @@ func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds
 	if err != nil {
 		return err
 	}
-	return d.inode.checkPermissions(creds, ats, d.inode.isDir())
+	return d.inode.checkPermissions(creds, ats)
 }
 
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
@@ -178,7 +178,7 @@ func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, op
 		if !d.inode.isDir() {
 			return nil, syserror.ENOTDIR
 		}
-		if err := d.inode.checkPermissions(rp.Credentials(), vfs.MayExec, true /* isDir */); err != nil {
+		if err := d.inode.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil {
 			return nil, err
 		}
 	}
@@ -301,7 +301,7 @@ afterTrailingSymlink:
 		return nil, err
 	}
 	// Check for search permission in the parent directory.
-	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayExec, true); err != nil {
+	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil {
 		return nil, err
 	}
 	// Reject attempts to open directories with O_CREAT.
@@ -316,7 +316,7 @@ afterTrailingSymlink:
 	child, err := stepLocked(rp, parent)
 	if err == syserror.ENOENT {
 		// Already checked for searchability above; now check for writability.
-		if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite, true); err != nil {
+		if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite); err != nil {
 			return nil, err
 		}
 		if err := rp.Mount().CheckBeginWrite(); err != nil {
@@ -347,7 +347,7 @@ afterTrailingSymlink:
 func (d *dentry) open(ctx context.Context, rp *vfs.ResolvingPath, opts *vfs.OpenOptions, afterCreate bool) (*vfs.FileDescription, error) {
 	ats := vfs.AccessTypesForOpenFlags(opts)
 	if !afterCreate {
-		if err := d.inode.checkPermissions(rp.Credentials(), ats, d.inode.isDir()); err != nil {
+		if err := d.inode.checkPermissions(rp.Credentials(), ats); err != nil {
 			return nil, err
 		}
 	}
@@ -428,7 +428,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 	defer mnt.EndWrite()
 
 	oldParent := oldParentVD.Dentry().Impl().(*dentry)
-	if err := oldParent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true /* isDir */); err != nil {
+	if err := oldParent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	// Call vfs.Dentry.Child() instead of stepLocked() or rp.ResolveChild(),
@@ -445,7 +445,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 		}
 		if oldParent != newParent {
 			// Writability is needed to change renamed's "..".
-			if err := renamed.inode.checkPermissions(rp.Credentials(), vfs.MayWrite, true /* isDir */); err != nil {
+			if err := renamed.inode.checkPermissions(rp.Credentials(), vfs.MayWrite); err != nil {
 				return err
 			}
 		}
@@ -455,7 +455,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 		}
 	}
 
-	if err := newParent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true /* isDir */); err != nil {
+	if err := newParent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	replacedVFSD := newParent.vfsd.Child(newName)
@@ -528,7 +528,7 @@ func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	if err != nil {
 		return err
 	}
-	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true /* isDir */); err != nil {
+	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	name := rp.Component()
@@ -621,7 +621,7 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	if err != nil {
 		return err
 	}
-	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec, true /* isDir */); err != nil {
+	if err := parent.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
 	}
 	name := rp.Component()
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index 2d5070a46..2f9e6c876 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -245,8 +245,9 @@ func (i *inode) decRef() {
 	}
 }
 
-func (i *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes, isDir bool) error {
-	return vfs.GenericCheckPermissions(creds, ats, isDir, uint16(atomic.LoadUint32(&i.mode)), auth.KUID(atomic.LoadUint32(&i.uid)), auth.KGID(atomic.LoadUint32(&i.gid)))
+func (i *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
+	mode := linux.FileMode(atomic.LoadUint32(&i.mode))
+	return vfs.GenericCheckPermissions(creds, ats, mode, auth.KUID(atomic.LoadUint32(&i.uid)), auth.KGID(atomic.LoadUint32(&i.gid)))
 }
 
 // Go won't inline this function, and returning linux.Statx (which is quite
@@ -299,7 +300,8 @@ func (i *inode) setStat(ctx context.Context, creds *auth.Credentials, stat *linu
 	if stat.Mask&^(linux.STATX_MODE|linux.STATX_UID|linux.STATX_GID|linux.STATX_ATIME|linux.STATX_MTIME|linux.STATX_CTIME|linux.STATX_SIZE) != 0 {
 		return syserror.EPERM
 	}
-	if err := vfs.CheckSetStat(ctx, creds, stat, uint16(atomic.LoadUint32(&i.mode))&^linux.S_IFMT, auth.KUID(atomic.LoadUint32(&i.uid)), auth.KGID(atomic.LoadUint32(&i.gid))); err != nil {
+	mode := linux.FileMode(atomic.LoadUint32(&i.mode))
+	if err := vfs.CheckSetStat(ctx, creds, stat, mode, auth.KUID(atomic.LoadUint32(&i.uid)), auth.KGID(atomic.LoadUint32(&i.gid))); err != nil {
 		return err
 	}
 	i.mu.Lock()
diff --git a/pkg/sentry/vfs/anonfs.go b/pkg/sentry/vfs/anonfs.go
index 925996517..a62e43589 100644
--- a/pkg/sentry/vfs/anonfs.go
+++ b/pkg/sentry/vfs/anonfs.go
@@ -83,7 +83,7 @@ func (fs *anonFilesystem) AccessAt(ctx context.Context, rp *ResolvingPath, creds
 	if !rp.Done() {
 		return syserror.ENOTDIR
 	}
-	return GenericCheckPermissions(creds, ats, false /* isDir */, anonFileMode, anonFileUID, anonFileGID)
+	return GenericCheckPermissions(creds, ats, anonFileMode, anonFileUID, anonFileGID)
 }
 
 // GetDentryAt implements FilesystemImpl.GetDentryAt.
diff --git a/pkg/sentry/vfs/permissions.go b/pkg/sentry/vfs/permissions.go
index 2c8f23f55..f9647f90e 100644
--- a/pkg/sentry/vfs/permissions.go
+++ b/pkg/sentry/vfs/permissions.go
@@ -29,9 +29,9 @@ type AccessTypes uint16
 
 // Bits in AccessTypes.
 const (
+	MayExec  AccessTypes = 1
+	MayWrite AccessTypes = 2
 	MayRead  AccessTypes = 4
-	MayWrite             = 2
-	MayExec              = 1
 )
 
 // OnlyRead returns true if access _only_ allows read.
@@ -56,16 +56,17 @@ func (a AccessTypes) MayExec() bool {
 
 // GenericCheckPermissions checks that creds has the given access rights on a
 // file with the given permissions, UID, and GID, subject to the rules of
-// fs/namei.c:generic_permission(). isDir is true if the file is a directory.
-func GenericCheckPermissions(creds *auth.Credentials, ats AccessTypes, isDir bool, mode uint16, kuid auth.KUID, kgid auth.KGID) error {
+// fs/namei.c:generic_permission().
+func GenericCheckPermissions(creds *auth.Credentials, ats AccessTypes, mode linux.FileMode, kuid auth.KUID, kgid auth.KGID) error {
 	// Check permission bits.
-	perms := mode
+	perms := uint16(mode.Permissions())
 	if creds.EffectiveKUID == kuid {
 		perms >>= 6
 	} else if creds.InGroup(kgid) {
 		perms >>= 3
 	}
 	if uint16(ats)&perms == uint16(ats) {
+		// All permission bits match, access granted.
 		return nil
 	}
 
@@ -77,7 +78,7 @@ func GenericCheckPermissions(creds *auth.Credentials, ats AccessTypes, isDir boo
 	}
 	// CAP_DAC_READ_SEARCH allows the caller to read and search arbitrary
 	// directories, and read arbitrary non-directory files.
-	if (isDir && !ats.MayWrite()) || ats.OnlyRead() {
+	if (mode.IsDir() && !ats.MayWrite()) || ats.OnlyRead() {
 		if creds.HasCapability(linux.CAP_DAC_READ_SEARCH) {
 			return nil
 		}
@@ -85,7 +86,7 @@ func GenericCheckPermissions(creds *auth.Credentials, ats AccessTypes, isDir boo
 	// CAP_DAC_OVERRIDE allows arbitrary access to directories, read/write
 	// access to non-directory files, and execute access to non-directory files
 	// for which at least one execute bit is set.
-	if isDir || !ats.MayExec() || (mode&0111 != 0) {
+	if mode.IsDir() || !ats.MayExec() || (mode.Permissions()&0111 != 0) {
 		if creds.HasCapability(linux.CAP_DAC_OVERRIDE) {
 			return nil
 		}
@@ -151,7 +152,7 @@ func MayWriteFileWithOpenFlags(flags uint32) bool {
 // CheckSetStat checks that creds has permission to change the metadata of a
 // file with the given permissions, UID, and GID as specified by stat, subject
 // to the rules of Linux's fs/attr.c:setattr_prepare().
-func CheckSetStat(ctx context.Context, creds *auth.Credentials, stat *linux.Statx, mode uint16, kuid auth.KUID, kgid auth.KGID) error {
+func CheckSetStat(ctx context.Context, creds *auth.Credentials, stat *linux.Statx, mode linux.FileMode, kuid auth.KUID, kgid auth.KGID) error {
 	if stat.Mask&linux.STATX_SIZE != 0 {
 		limit, err := CheckLimit(ctx, 0, int64(stat.Size))
 		if err != nil {
@@ -190,11 +191,7 @@ func CheckSetStat(ctx context.Context, creds *auth.Credentials, stat *linux.Stat
 				(stat.Mask&linux.STATX_CTIME != 0 && stat.Ctime.Nsec != linux.UTIME_NOW) {
 				return syserror.EPERM
 			}
-			// isDir is irrelevant in the following call to
-			// GenericCheckPermissions since ats == MayWrite means that
-			// CAP_DAC_READ_SEARCH does not apply, and CAP_DAC_OVERRIDE
-			// applies, regardless of isDir.
-			if err := GenericCheckPermissions(creds, MayWrite, false /* isDir */, mode, kuid, kgid); err != nil {
+			if err := GenericCheckPermissions(creds, MayWrite, mode, kuid, kgid); err != nil {
 				return err
 			}
 		}