seccomp: always propagate NO_NEW_PRIVS on tsync

commit 103502a35cfce0710909da874f092cb44823ca03 upstream.

Before this patch, a process with some permissive seccomp filter
that was applied by root without NO_NEW_PRIVS was able to add
more filters to itself without setting NO_NEW_PRIVS by setting
the new filter from a throwaway thread with NO_NEW_PRIVS.

Signed-off-by: Jann Horn <jann@thejh.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 580ac2d4024ffbdb29960ccdd86424fa730b1e78..15a1795bbba17d1140e3220c41d48dd26ac43c95 100644 (file)
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -316,24 +316,24 @@ static inline void seccomp_sync_threads(void)
                put_seccomp_filter(thread);
                smp_store_release(&thread->seccomp.filter,
                                  caller->seccomp.filter);
+
+               /*
+                * Don't let an unprivileged task work around
+                * the no_new_privs restriction by creating
+                * a thread that sets it up, enters seccomp,
+                * then dies.
+                */
+               if (task_no_new_privs(caller))
+                       task_set_no_new_privs(thread);
+
                /*
                 * Opt the other thread into seccomp if needed.
                 * As threads are considered to be trust-realm
                 * equivalent (see ptrace_may_access), it is safe to
                 * allow one thread to transition the other.
                 */
-               if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) {
-                       /*
-                        * Don't let an unprivileged task work around
-                        * the no_new_privs restriction by creating
-                        * a thread that sets it up, enters seccomp,
-                        * then dies.
-                        */
-                       if (task_no_new_privs(caller))
-                               task_set_no_new_privs(thread);
-
+               if (thread->seccomp.mode == SECCOMP_MODE_DISABLED)
                        seccomp_assign_mode(thread, SECCOMP_MODE_FILTER);
-               }
        }
 }