virt: use read_virtual_file() for reading /proc/self/setgroups

src/basic/virt.c

@@ -836,19 +836,18 @@ int running_in_userns(void) {
         if (r != 0)
                 return r;
 
-        /* "setgroups" file was added in kernel v3.18-rc6-15-g9cc46516dd. It is also
-         * possible to compile a kernel without CONFIG_USER_NS, in which case "setgroups"
-         * also does not exist. We cannot distinguish those two cases, so assume that
-         * we're running on a stripped-down recent kernel, rather than on an old one,
-         * and if the file is not found, return false.
-         */
-        r = read_one_line_file("/proc/self/setgroups", &line);
+        /* "setgroups" file was added in kernel v3.18-rc6-15-g9cc46516dd. It is also possible to compile a
+         * kernel without CONFIG_USER_NS, in which case "setgroups" also does not exist. We cannot
+         * distinguish those two cases, so assume that we're running on a stripped-down recent kernel, rather
+         * than on an old one, and if the file is not found, return false. */
+        r = read_virtual_file("/proc/self/setgroups", SIZE_MAX, &line, NULL);
         if (r < 0) {
                 log_debug_errno(r, "/proc/self/setgroups: %m");
                 return r == -ENOENT ? false : r;
         }
 
-        truncate_nl(line);
+        strstrip(line); /* remove trailing newline */
+
         r = streq(line, "deny");
         /* See user_namespaces(7) for a description of this "setgroups" contents. */
         log_debug("/proc/self/setgroups contains \"%s\", %s user namespace", line, r ? "in" : "not in");