nspawn: make /dev/kmsg unavailable in the container, but allow access to /proc/kmsg

2 files changed, 10 insertions, 1 deletions

diff --git a/Makefile.am b/Makefile.am
index a2087820e7..22a04d4a1b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -3123,7 +3123,6 @@ systemd-install-data-hook:
 		$(LN_S) ../system-services/org.freedesktop.systemd1.service org.freedesktop.systemd1.service )
 if HAVE_PLYMOUTH
 	$(MKDIR_P) -m 0755 \
-		$(DESTDIR)$(SYSTEM_SYSVINIT_PATH) \
 		$(DESTDIR)$(systemunitdir)/reboot.target.wants \
 		$(DESTDIR)$(systemunitdir)/kexec.target.wants \
 		$(DESTDIR)$(systemunitdir)/poweroff.target.wants \
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 90c8b94248..71cdd3f39f 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -394,6 +394,13 @@ static int setup_kmsg(const char *dest, int kmsg_socket) {
 
         u = umask(0000);
 
+        /* We create the kmsg FIFO as /dev/kmsg, but immediately
+         * delete it after bind mounting it to /proc/kmsg. While FIFOs
+         * on the reading side behave very similar to /proc/kmsg,
+         * their writing side behaves differently from /dev/kmsg in
+         * that writing blocks when nothing is reading. In order to
+         * avoid any problems with containers deadlocking due to this
+         * we simply make /dev/kmsg unavailable to the container. */
         if (asprintf(&from, "%s/dev/kmsg", dest) < 0) {
                 log_error("Out of memory");
                 r = -ENOMEM;
@@ -456,6 +463,9 @@ static int setup_kmsg(const char *dest, int kmsg_socket) {
                 goto finish;
         }
 
+        /* And now make the FIFO unavailable as /dev/kmsg... */
+        unlink(from);
+
 finish:
         free(from);
         free(to);