Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751605AbdITNhd (ORCPT ); Wed, 20 Sep 2017 09:37:33 -0400 Received: from mail-oi0-f53.google.com ([209.85.218.53]:49472 "EHLO mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751228AbdITNhc (ORCPT ); Wed, 20 Sep 2017 09:37:32 -0400 X-Google-Smtp-Source: AOwi7QDtjZAV8oMZk1+yPKQ8/g0oq2g1p6WPfU2dr5qlKDHMMYGWPE7cZBODyCRkYAXq78BG3lg1QA== Date: Wed, 20 Sep 2017 07:37:26 -0600 From: Tycho Andersen To: Oleg Nesterov Cc: Chris Salls , Kees Cook , Andy Lutomirski , Will Drewry , security@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter() Message-ID: <20170920133726.dwqkovxcf34ot4vl@docker> References: <20170920125621.GA3599@redhat.com> <20170920130443.GA4445@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170920130443.GA4445@redhat.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3261 Lines: 120 On Wed, Sep 20, 2017 at 03:04:43PM +0200, Oleg Nesterov wrote: > 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? Yes, this looks good to me, thanks. > And I can't understand the SECCOMP_MODE_DISABLED check... shouldn't we > simply remove it? I think the idea was to prevent some interaction between seccomp+ptrace+fork that we didn't understand. Since the user of this code doesn't have seccomp filters attached, it was fine. Thanks for cleaning this up, I'll be happy to test whatever final patch we come up with. Tycho > 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 >