Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751976AbdITNEq (ORCPT ); Wed, 20 Sep 2017 09:04:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37488 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751653AbdITNEp (ORCPT ); Wed, 20 Sep 2017 09:04:45 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A41142C976D Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=oleg@redhat.com Date: Wed, 20 Sep 2017 15:04:43 +0200 From: Oleg Nesterov To: Chris Salls , Kees Cook , Andy Lutomirski , Will Drewry Cc: security@kernel.org, linux-kernel@vger.kernel.org, Tycho Andersen Subject: Re: [PATCH] seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter() Message-ID: <20170920130443.GA4445@redhat.com> References: <20170920125621.GA3599@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170920125621.GA3599@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 20 Sep 2017 13:04:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2666 Lines: 107 On 09/20, Oleg Nesterov wrote: > > @@ -908,13 +912,13 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, > if (!data) > goto out; > > - get_seccomp_filter(task); > + refcount_inc(&filter->usage); > 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); This is the simple fix for -stable, but again, can't we simplify this code? Afaics we can do get_seccomp_filter() at the start and drop siglock right after that. Something like the untested patch (on top of this one) below? And I can't understand the SECCOMP_MODE_DISABLED check... shouldn't we simply remove it? Oleg. --- x/kernel/seccomp.c +++ x/kernel/seccomp.c @@ -858,45 +858,36 @@ long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, void __user *data) { - struct seccomp_filter *filter; + struct seccomp_filter *orig, *filter; struct sock_fprog_kern *fprog; + unsigned long count; long ret; - unsigned long count = 0; if (!capable(CAP_SYS_ADMIN) || current->seccomp.mode != SECCOMP_MODE_DISABLED) { return -EACCES; } + if (task->seccomp.mode != SECCOMP_MODE_FILTER) + return -EINVAL; + spin_lock_irq(&task->sighand->siglock); - if (task->seccomp.mode != SECCOMP_MODE_FILTER) { - ret = -EINVAL; - goto out; - } + get_seccomp_filter(task); + orig = task->seccomp.filter; + spin_unlock_irq(&task->sighand->siglock); - filter = task->seccomp.filter; - while (filter) { - filter = filter->prev; + count = 0; + for (filter = orig; filter; filter = filter->prev) count++; - } if (filter_off >= count) { ret = -ENOENT; goto out; } - count -= filter_off; - filter = task->seccomp.filter; - while (filter && count > 1) { - filter = filter->prev; + count -= filter_off; + for (filter = orig; count > 1; filter = filter->prev) count--; - } - - if (WARN_ON(count != 1 || !filter)) { - /* The filter tree shouldn't shrink while we're using it. */ - ret = -ENOENT; - goto out; - } fprog = filter->prog->orig_prog; if (!fprog) { @@ -912,17 +903,11 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, if (!data) goto out; - refcount_inc(&filter->usage); - spin_unlock_irq(&task->sighand->siglock); - if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) ret = -EFAULT; - __put_seccomp_filter(filter); - return ret; - out: - spin_unlock_irq(&task->sighand->siglock); + __put_seccomp_filter(orig); return ret; } #endif