Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751824AbdITP7l (ORCPT ); Wed, 20 Sep 2017 11:59:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64046 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751785AbdITP7k (ORCPT ); Wed, 20 Sep 2017 11:59:40 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 4D7B87EA9E Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=oleg@redhat.com Date: Wed, 20 Sep 2017 17:59:37 +0200 From: Oleg Nesterov To: Tycho Andersen Cc: Chris Salls , Kees Cook , Andy Lutomirski , Will Drewry , security@kernel.org, linux-kernel@vger.kernel.org Subject: introduce get_nth_filter() Message-ID: <20170920155937.GA25572@redhat.com> References: <20170920125621.GA3599@redhat.com> <20170920130443.GA4445@redhat.com> <20170920133726.dwqkovxcf34ot4vl@docker> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170920133726.dwqkovxcf34ot4vl@docker> 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 [10.5.110.28]); Wed, 20 Sep 2017 15:59:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3106 Lines: 121 On 09/20, Tycho Andersen wrote: > > Thanks for cleaning this up, I'll be happy to test whatever final > patch we come up with. Well, I just noticed you sent another "[PATCH] ptrace, seccomp: add support for retrieving seccomp flags" today... So if we need get_nth() helper please consider the UNTESTED change below (on top of this fix). If you agree with this code, feel free to incorporate it into your patch. Oleg. --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -855,49 +855,54 @@ long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) } #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) -long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, - void __user *data) +static struct seccomp_filter * +get_nth_filter(struct task_struct *task, unsigned long filter_off) { - struct seccomp_filter *filter; - struct sock_fprog_kern *fprog; - long ret; - unsigned long count = 0; + struct seccomp_filter *orig, *filter; + unsigned long count; - if (!capable(CAP_SYS_ADMIN) || - current->seccomp.mode != SECCOMP_MODE_DISABLED) { - return -EACCES; - } + if (task->seccomp.mode != SECCOMP_MODE_FILTER) + return ERR_PTR(-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; + filter = ERR_PTR(-ENOENT); + if (filter_off >= count) 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; + refcount_inc(&filter->usage); +out: + __put_seccomp_filter(orig); + return filter; +} + +long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, + void __user *data) +{ + struct seccomp_filter *filter; + struct sock_fprog_kern *fprog; + long ret; + + if (!capable(CAP_SYS_ADMIN) || + current->seccomp.mode != SECCOMP_MODE_DISABLED) { + return -EACCES; } + filter = get_nth_filter(task, filter_off); + if (IS_ERR(filter)) + return PTR_ERR(filter); + fprog = filter->prog->orig_prog; if (!fprog) { /* This must be a new non-cBPF filter, since we save @@ -912,17 +917,10 @@ 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(filter); return ret; } #endif