From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752656AbdJCMWO (ORCPT ); Tue, 3 Oct 2017 08:22:14 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:60028 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752594AbdJCMWM (ORCPT ); Tue, 3 Oct 2017 08:22:12 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Chris Salls , Oleg Nesterov , Tycho Andersen , Kees Cook Subject: [PATCH 4.4 21/41] seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter() Date: Tue, 3 Oct 2017 14:21:22 +0200 Message-Id: <20171003114221.187140436@linuxfoundation.org> X-Mailer: git-send-email 2.14.2 In-Reply-To: <20171003114219.900672076@linuxfoundation.org> References: <20171003114219.900672076@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit 66a733ea6b611aecf0119514d2dddab5f9d6c01e upstream. As Chris explains, get_seccomp_filter() and put_seccomp_filter() can end up using different filters. Once we drop ->siglock it is possible for task->seccomp.filter to have been replaced by SECCOMP_FILTER_FLAG_TSYNC. Fixes: f8e529ed941b ("seccomp, ptrace: add support for dumping seccomp filters") Reported-by: Chris Salls Signed-off-by: Oleg Nesterov [tycho: add __get_seccomp_filter vs. open coding refcount_inc()] Signed-off-by: Tycho Andersen [kees: tweak commit log] Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman --- kernel/seccomp.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -457,14 +457,19 @@ static long seccomp_attach_filter(unsign return 0; } +void __get_seccomp_filter(struct seccomp_filter *filter) +{ + /* Reference count is bounded by the number of total processes. */ + atomic_inc(&filter->usage); +} + /* get_seccomp_filter - increments the reference count of the filter on @tsk */ void get_seccomp_filter(struct task_struct *tsk) { struct seccomp_filter *orig = tsk->seccomp.filter; if (!orig) return; - /* Reference count is bounded by the number of total processes. */ - atomic_inc(&orig->usage); + __get_seccomp_filter(orig); } static inline void seccomp_filter_free(struct seccomp_filter *filter) @@ -475,10 +480,8 @@ static inline void seccomp_filter_free(s } } -/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ -void put_seccomp_filter(struct task_struct *tsk) +static void __put_seccomp_filter(struct seccomp_filter *orig) { - struct seccomp_filter *orig = tsk->seccomp.filter; /* Clean up single-reference branches iteratively. */ while (orig && atomic_dec_and_test(&orig->usage)) { struct seccomp_filter *freeme = orig; @@ -487,6 +490,12 @@ void put_seccomp_filter(struct task_stru } } +/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ +void put_seccomp_filter(struct task_struct *tsk) +{ + __put_seccomp_filter(tsk->seccomp.filter); +} + /** * seccomp_send_sigsys - signals the task to allow in-process syscall emulation * @syscall: syscall number to send to userland @@ -927,13 +936,13 @@ long seccomp_get_filter(struct task_stru if (!data) goto out; - get_seccomp_filter(task); + __get_seccomp_filter(filter); spin_unlock_irq(&task->sighand->siglock); if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) ret = -EFAULT; - put_seccomp_filter(task); + __put_seccomp_filter(filter); return ret; out: