nsenter: Do not try to enter nonexisting namespaces when --all is used

This PR changes is_same_namespace() to is_usable_namespace(). If a namespace file
is missing for the running PID, then it is considered not usable and we do not try
to enter it.

Signed-off-by: Yonatan Goldschmidt <yon.goldschmidt@gmail.com>

diff --git a/sys-utils/nsenter.c b/sys-utils/nsenter.c
index 8eac7800b0067c321c553b0b450fedaa7121b0bc..6bdfc0d4a4ad6dea3bd376192885a4b0335c23e8 100644 (file)
--- a/sys-utils/nsenter.c
+++ b/sys-utils/nsenter.c
@@ -156,20 +156,33 @@ static int get_ns_ino(const char *path, ino_t *ino)
        return 0;
 }
 
-static int is_same_namespace(pid_t a, pid_t b, const char *type)
+static int is_usable_namespace(pid_t target, const struct namespace_file *nsfile)
 {
        char path[PATH_MAX];
-       ino_t a_ino = 0, b_ino = 0;
+       ino_t my_ino = 0;
+       int rc;
 
-       snprintf(path, sizeof(path), "/proc/%u/%s", a, type);
-       if (get_ns_ino(path, &a_ino) != 0)
-               err(EXIT_FAILURE, _("stat of %s failed"), path);
+       /* Check NS accessibility */
+       snprintf(path, sizeof(path), "/proc/%u/%s", getpid(), nsfile->name);
+       rc = get_ns_ino(path, &my_ino);
+       if (rc == -ENOENT)
+               return false; /* Unsupported NS */
 
-       snprintf(path, sizeof(path), "/proc/%u/%s", b, type);
-       if (get_ns_ino(path, &b_ino) != 0)
-               err(EXIT_FAILURE, _("stat of %s failed"), path);
+       /* It is not permitted to use setns(2) to reenter the caller's
+        * current user namespace; see setns(2) man page for more details.
+        */
+       if (nsfile->nstype & CLONE_NEWUSER) {
+               ino_t target_ino = 0;
+
+               snprintf(path, sizeof(path), "/proc/%u/%s", target, nsfile->name);
+               if (get_ns_ino(path, &target_ino) != 0)
+                       err(EXIT_FAILURE, _("stat of %s failed"), path);
+
+               if (my_ino == target_ino)
+                       return false;
+       }
 
-       return a_ino == b_ino;
+       return true; /* All pass */
 }
 
 static void continue_as_child(void)
@@ -371,11 +384,7 @@ int main(int argc, char *argv[])
                        if (nsfile->fd >= 0)
                                continue;       /* namespace already specified */
 
-                       /* It is not permitted to use setns(2) to reenter the caller's
-                        * current user namespace; see setns(2) man page for more details.
-                        */
-                       if (nsfile->nstype & CLONE_NEWUSER
-                           && is_same_namespace(getpid(), namespace_target_pid, nsfile->name))
+                       if (!is_usable_namespace(namespace_target_pid, nsfile))
                                continue;
 
                        namespaces |= nsfile->nstype;