seccomp: always propagate NO_NEW_PRIVS on tsync

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>
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 11 insertions, 11 deletions

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 580ac2d4024f..15a1795bbba1 100644
--- 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);
-                }
         }
 }