rootless: add function to join user and mount namespace

Add the possibility to join directly the user and mount namespace
without looking up the parent of the user namespace.

We need this in order to be able the conmon process, as the mount
namespace is kept alive only there.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/pkg/rootless/rootless_linux.c b/pkg/rootless/rootless_linux.c
index 9eb16c1a5..1d28ff68d 100644
--- a/pkg/rootless/rootless_linux.c
+++ b/pkg/rootless/rootless_linux.c
@@ -99,7 +99,7 @@ get_cmd_line_args (pid_t pid)
 }
 
 int
-reexec_userns_join (int userns)
+reexec_userns_join (int userns, int mountns)
 {
   pid_t ppid = getpid ();
   char uid[16];
@@ -131,6 +131,13 @@ reexec_userns_join (int userns)
     }
   close (userns);
 
+  if (mountns >= 0 && setns (mountns, 0) < 0)
+    {
+      fprintf (stderr, "cannot setns: %s\n", strerror (errno));
+      _exit (EXIT_FAILURE);
+    }
+  close (userns);
+
   if (syscall_setresgid (0, 0, 0) < 0)
     {
       fprintf (stderr, "cannot setresgid: %s\n", strerror (errno));