futex: Nullify robust lists after cleanup

commit fc6b177dee33365ccb29fe6d2092223cf8d679f9 upstream.

The robust list pointers of user space held futexes are kept intact
over an exec() call. When the exec'ed task exits exit_robust_list() is
called with the stale pointer. The risk of corruption is minimal, but
still it is incorrect to keep the pointers valid. Actually glibc
should uninstall the robust list before calling exec() but we have to
deal with it anyway.

Nullify the pointers after [compat_]exit_robust_list() has been
called.

Reported-by: Anirban Sinha <ani@anirban.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/fork.c b/kernel/fork.c
index edd0b2dfbce8a1aa40eca8a4ce0a5b9e36b907d5..4b36858c0f4ab8e0623a38ca52be8632a6cff5a6 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -544,11 +544,15 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 
        /* Get rid of any futexes when releasing the mm */
 #ifdef CONFIG_FUTEX
-       if (unlikely(tsk->robust_list))
+       if (unlikely(tsk->robust_list)) {
                exit_robust_list(tsk);
+               tsk->robust_list = NULL;
+       }
 #ifdef CONFIG_COMPAT
-       if (unlikely(tsk->compat_robust_list))
+       if (unlikely(tsk->compat_robust_list)) {
                compat_exit_robust_list(tsk);
+               tsk->compat_robust_list = NULL;
+       }
 #endif
        if (unlikely(!list_empty(&tsk->pi_state_list)))
                exit_pi_state_list(tsk);