rootless: block signals on re-exec

we are allowed to use only signal safe functions between a fork of a
multithreaded application and the next execve.  Since setenv(3) is not
signal safe, block signals.  We are already doing it for creating a
new namespace.

This is mostly a cleanup since reexec_in_user_namespace_wait is used
only only to join existing namespaces when we have not a pause.pid
file.

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

1 files changed, 22 insertions, 0 deletions

diff --git a/pkg/rootless/rootless_linux.c b/pkg/rootless/rootless_linux.c
index a2425c83e..eb62d55e9 100644
--- a/pkg/rootless/rootless_linux.c
+++ b/pkg/rootless/rootless_linux.c
@@ -489,6 +489,7 @@ reexec_userns_join (int userns, int mountns, char *pause_pid_file_path)
   char **argv;
   int pid;
   char *cwd = getcwd (NULL, 0);
+  sigset_t sigset, oldsigset;
 
   if (cwd == NULL)
     {
@@ -522,6 +523,22 @@ reexec_userns_join (int userns, int mountns, char *pause_pid_file_path)
       return pid;
     }
 
+  if (sigfillset (&sigset) < 0)
+    {
+      fprintf (stderr, "cannot fill sigset: %s\n", strerror (errno));
+      _exit (EXIT_FAILURE);
+    }
+  if (sigdelset (&sigset, SIGCHLD) < 0)
+    {
+      fprintf (stderr, "cannot sigdelset(SIGCHLD): %s\n", strerror (errno));
+      _exit (EXIT_FAILURE);
+    }
+  if (sigprocmask (SIG_BLOCK, &sigset, &oldsigset) < 0)
+    {
+      fprintf (stderr, "cannot block signals: %s\n", strerror (errno));
+      _exit (EXIT_FAILURE);
+    }
+
   setenv ("_CONTAINERS_USERNS_CONFIGURED", "init", 1);
   setenv ("_CONTAINERS_ROOTLESS_UID", uid, 1);
   setenv ("_CONTAINERS_ROOTLESS_GID", gid, 1);
@@ -570,6 +587,11 @@ reexec_userns_join (int userns, int mountns, char *pause_pid_file_path)
       /* We ignore errors here as we didn't create the namespace anyway.  */
       create_pause_process (pause_pid_file_path, argv);
     }
+  if (sigprocmask (SIG_SETMASK, &oldsigset, NULL) < 0)
+    {
+      fprintf (stderr, "cannot block signals: %s\n", strerror (errno));
+      _exit (EXIT_FAILURE);
+    }
 
   execvp (argv[0], argv);