Minor VFS2 xattr changes.

- Allow the gofer client to use most xattr namespaces. As documented by the
  updated comment, this is consistent with e.g. Linux's FUSE client, and allows
  gofers to provide extended attributes from FUSE filesystems.

- Make tmpfs' listxattr omit xattrs in the "trusted" namespace for
  non-privileged users.

PiperOrigin-RevId: 378778854

pkg/sentry/fsimpl/tmpfs/filesystem.go

@@ -822,7 +822,7 @@ func (fs *filesystem) ListXattrAt(ctx context.Context, rp *vfs.ResolvingPath, si
 	if err != nil {
 		return nil, err
 	}
-	return d.inode.listXattr(size)
+	return d.inode.listXattr(rp.Credentials(), size)
 }
 
 // GetXattrAt implements vfs.FilesystemImpl.GetXattrAt.

pkg/sentry/fsimpl/tmpfs/tmpfs.go

@@ -717,44 +717,63 @@ func (i *inode) touchCMtimeLocked() {
 	atomic.StoreInt64(&i.ctime, now)
 }
 
-func (i *inode) listXattr(size uint64) ([]string, error) {
-	return i.xattrs.ListXattr(size)
+func checkXattrName(name string) error {
+	// Linux's tmpfs supports "security" and "trusted" xattr namespaces, and
+	// (depending on build configuration) POSIX ACL xattr namespaces
+	// ("system.posix_acl_access" and "system.posix_acl_default"). We don't
+	// support POSIX ACLs or the "security" namespace (b/148380782).
+	if strings.HasPrefix(name, linux.XATTR_TRUSTED_PREFIX) {
+		return nil
+	}
+	// We support the "user" namespace because we have tests that depend on
+	// this feature.
+	if strings.HasPrefix(name, linux.XATTR_USER_PREFIX) {
+		return nil
+	}
+	return syserror.EOPNOTSUPP
+}
+
+func (i *inode) listXattr(creds *auth.Credentials, size uint64) ([]string, error) {
+	return i.xattrs.ListXattr(creds, size)
 }
 
 func (i *inode) getXattr(creds *auth.Credentials, opts *vfs.GetXattrOptions) (string, error) {
-	if err := i.checkXattrPermissions(creds, opts.Name, vfs.MayRead); err != nil {
+	if err := checkXattrName(opts.Name); err != nil {
 		return "", err
 	}
-	return i.xattrs.GetXattr(opts)
-}
-
-func (i *inode) setXattr(creds *auth.Credentials, opts *vfs.SetXattrOptions) error {
-	if err := i.checkXattrPermissions(creds, opts.Name, vfs.MayWrite); err != nil {
-		return err
-	}
-	return i.xattrs.SetXattr(opts)
-}
-
-func (i *inode) removeXattr(creds *auth.Credentials, name string) error {
-	if err := i.checkXattrPermissions(creds, name, vfs.MayWrite); err != nil {
-		return err
-	}
-	return i.xattrs.RemoveXattr(name)
-}
-
-func (i *inode) checkXattrPermissions(creds *auth.Credentials, name string, ats vfs.AccessTypes) error {
-	// We currently only support extended attributes in the user.* and
-	// trusted.* namespaces. See b/148380782.
-	if !strings.HasPrefix(name, linux.XATTR_USER_PREFIX) && !strings.HasPrefix(name, linux.XATTR_TRUSTED_PREFIX) {
-		return syserror.EOPNOTSUPP
-	}
 	mode := linux.FileMode(atomic.LoadUint32(&i.mode))
 	kuid := auth.KUID(atomic.LoadUint32(&i.uid))
 	kgid := auth.KGID(atomic.LoadUint32(&i.gid))
-	if err := vfs.GenericCheckPermissions(creds, ats, mode, kuid, kgid); err != nil {
+	if err := vfs.GenericCheckPermissions(creds, vfs.MayRead, mode, kuid, kgid); err != nil {
+		return "", err
+	}
+	return i.xattrs.GetXattr(creds, mode, kuid, opts)
+}
+
+func (i *inode) setXattr(creds *auth.Credentials, opts *vfs.SetXattrOptions) error {
+	if err := checkXattrName(opts.Name); err != nil {
 		return err
 	}
-	return vfs.CheckXattrPermissions(creds, ats, mode, kuid, name)
+	mode := linux.FileMode(atomic.LoadUint32(&i.mode))
+	kuid := auth.KUID(atomic.LoadUint32(&i.uid))
+	kgid := auth.KGID(atomic.LoadUint32(&i.gid))
+	if err := vfs.GenericCheckPermissions(creds, vfs.MayWrite, mode, kuid, kgid); err != nil {
+		return err
+	}
+	return i.xattrs.SetXattr(creds, mode, kuid, opts)
+}
+
+func (i *inode) removeXattr(creds *auth.Credentials, name string) error {
+	if err := checkXattrName(name); err != nil {
+		return err
+	}
+	mode := linux.FileMode(atomic.LoadUint32(&i.mode))
+	kuid := auth.KUID(atomic.LoadUint32(&i.uid))
+	kgid := auth.KGID(atomic.LoadUint32(&i.gid))
+	if err := vfs.GenericCheckPermissions(creds, vfs.MayWrite, mode, kuid, kgid); err != nil {
+		return err
+	}
+	return i.xattrs.RemoveXattr(creds, mode, kuid, name)
 }
 
 // fileDescription is embedded by tmpfs implementations of
@@ -807,7 +826,7 @@ func (fd *fileDescription) StatFS(ctx context.Context) (linux.Statfs, error) {
 
 // ListXattr implements vfs.FileDescriptionImpl.ListXattr.
 func (fd *fileDescription) ListXattr(ctx context.Context, size uint64) ([]string, error) {
-	return fd.inode().listXattr(size)
+	return fd.inode().listXattr(auth.CredentialsFromContext(ctx), size)
 }
 
 // GetXattr implements vfs.FileDescriptionImpl.GetXattr.