pkg/archive: allow mknodding FIFO inside userns

Fix #41803

Also attempt to mknod devices.
Mknodding devices are likely to fail, but still worth trying when
running with a seccomp user notification.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

pkg/archive/archive_unix.go

@@ -81,11 +81,6 @@ func getFileUIDGID(stat interface{}) (idtools.Identity, error) {
 // handleTarTypeBlockCharFifo is an OS-specific helper function used by
 // createTarFile to handle the following types of header: Block; Char; Fifo
 func handleTarTypeBlockCharFifo(hdr *tar.Header, path string) error {
-	if sys.RunningInUserNS() {
-		// cannot create a device if running in user namespace
-		return nil
-	}
-
 	mode := uint32(hdr.Mode & 07777)
 	switch hdr.Typeflag {
 	case tar.TypeBlock:
@@ -96,7 +91,12 @@ func handleTarTypeBlockCharFifo(hdr *tar.Header, path string) error {
 		mode |= unix.S_IFIFO
 	}
 
-	return system.Mknod(path, mode, int(system.Mkdev(hdr.Devmajor, hdr.Devminor)))
+	err := system.Mknod(path, mode, int(system.Mkdev(hdr.Devmajor, hdr.Devminor)))
+	if errors.Is(err, syscall.EPERM) && sys.RunningInUserNS() {
+		// In most cases, cannot create a device if running in user namespace
+		err = nil
+	}
+	return err
 }
 
 func handleLChmod(hdr *tar.Header, path string, hdrInfo os.FileInfo) error {