From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:60202 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728637AbeIMSwK (ORCPT ); Thu, 13 Sep 2018 14:52:10 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , Michal Hocko , Andrew Morton , Rik van Riel , "Peter Zijlstra (Intel)" , Kees Cook , Oleg Nesterov , Linus Torvalds , Sasha Levin Subject: [PATCH 4.14 025/115] fork: dont copy inconsistent signal handler state to child Date: Thu, 13 Sep 2018 15:30:45 +0200 Message-Id: <20180913131825.157447412@linuxfoundation.org> In-Reply-To: <20180913131823.327472833@linuxfoundation.org> References: <20180913131823.327472833@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn [ Upstream commit 06e62a46bbba20aa5286102016a04214bb446141 ] Before this change, if a multithreaded process forks while one of its threads is changing a signal handler using sigaction(), the memcpy() in copy_sighand() can race with the struct assignment in do_sigaction(). It isn't clear whether this can cause corruption of the userspace signal handler pointer, but it definitely can cause inconsistency between different fields of struct sigaction. Take the appropriate spinlock to avoid this. I have tested that this patch prevents inconsistency between sa_sigaction and sa_flags, which is possible before this patch. Link: http://lkml.kernel.org/r/20180702145108.73189-1-jannh@google.com Signed-off-by: Jann Horn Acked-by: Michal Hocko Reviewed-by: Andrew Morton Cc: Rik van Riel Cc: "Peter Zijlstra (Intel)" Cc: Kees Cook Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/fork.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1350,7 +1350,9 @@ static int copy_sighand(unsigned long cl return -ENOMEM; atomic_set(&sig->count, 1); + spin_lock_irq(¤t->sighand->siglock); memcpy(sig->action, current->sighand->action, sizeof(sig->action)); + spin_unlock_irq(¤t->sighand->siglock); return 0; }