From fa1edf3f63c05ca8eacafcd7048ed91e5360f1a8 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Mon, 11 Sep 2017 11:24:22 +0200 Subject: [PATCH] s390/guarded storage: fix possible memory corruption For PREEMPT enabled kernels the guarded storage (GS) code contains a possible use-after-free bug. If a task that makes use of GS exits, it will execute do_exit() while still enabled for preemption. That function will call exit_thread_runtime_instr() via exit_thread(). If exit_thread_gs() gets preempted after the GS control block of the task has been freed but before the pointer to it is set to NULL, then save_gs_cb(), called from switch_to(), will write to already freed memory. Avoid this and simply disable preemption while freeing the control block and setting the pointer to NULL. Fixes: 916cda1aa1b4 ("s390: add a system call for guarded storage") Cc: # v4.12+ Reviewed-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/guarded_storage.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/s390/kernel/guarded_storage.c b/arch/s390/kernel/guarded_storage.c index 6f064745c3b1..4920cf6ffa00 100644 --- a/arch/s390/kernel/guarded_storage.c +++ b/arch/s390/kernel/guarded_storage.c @@ -13,9 +13,11 @@ void exit_thread_gs(void) { + preempt_disable(); kfree(current->thread.gs_cb); kfree(current->thread.gs_bc_cb); current->thread.gs_cb = current->thread.gs_bc_cb = NULL; + preempt_enable(); } static int gs_enable(void)