From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754121AbZFXDGa (ORCPT ); Tue, 23 Jun 2009 23:06:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751248AbZFXDGY (ORCPT ); Tue, 23 Jun 2009 23:06:24 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:38666 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751220AbZFXDGY (ORCPT ); Tue, 23 Jun 2009 23:06:24 -0400 Date: Tue, 23 Jun 2009 22:06:27 -0500 From: "Serge E. Hallyn" To: Oleg Nesterov Cc: Andrew Morton , Christoph Hellwig , James Morris , Ingo Molnar , Chris Wright , Roland McGrath , linux-kernel@vger.kernel.org, Al Viro , linux-security-module@vger.kernel.org Subject: Re: [PATCH 1/1] mm_for_maps: simplify, use ptrace_may_access() Message-ID: <20090624030627.GA6459@us.ibm.com> References: <20090507085742.GB3036@sequoia.sous-sol.org> <20090507090459.GE19133@elte.hu> <20090507092009.GC3036@sequoia.sous-sol.org> <20090507102015.GB8901@elte.hu> <20090623141451.GA8133@redhat.com> <20090623174918.GA24430@infradead.org> <20090623192451.GA27853@redhat.com> <20090623192532.GB27853@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090623192532.GB27853@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Oleg Nesterov (oleg@redhat.com): > It would be nice to kill __ptrace_may_access(). It requires task_lock(), > but this lock is only needed to read mm->flags in the middle. > > Convert mm_for_maps() to use ptrace_may_access(), this also simplifies > the code a little bit. > > Also, we do not need to take ->mmap_sem in advance. In fact I think > mm_for_maps() should not play with ->mmap_sem at all, the caller should > take this lock. Yeah I think that makes sense. > With or without this patch, without ->cred_guard_mutex held we can race > with exec() and get the new ->mm but check old creds. > > Signed-off-by: Oleg Nesterov reasoning on the security check also makes sense. Reviewed-by: Serge Hallyn > --- WAIT/fs/proc/base.c~1_MM_FOR_MAPS 2009-06-17 14:11:26.000000000 +0200 > +++ WAIT/fs/proc/base.c 2009-06-23 20:16:44.000000000 +0200 > @@ -237,20 +237,19 @@ struct mm_struct *mm_for_maps(struct tas > struct mm_struct *mm = get_task_mm(task); > if (!mm) > return NULL; > + if (mm != current->mm) { > + /* > + * task->mm can be changed before security check, > + * in that case we must notice the change after. > + */ > + if (!ptrace_may_access(task, PTRACE_MODE_READ) || > + mm != task->mm) { > + mmput(mm); > + return NULL; > + } > + } > down_read(&mm->mmap_sem); > - task_lock(task); > - if (task->mm != mm) > - goto out; > - if (task->mm != current->mm && > - __ptrace_may_access(task, PTRACE_MODE_READ) < 0) > - goto out; > - task_unlock(task); > return mm; > -out: > - task_unlock(task); > - up_read(&mm->mmap_sem); > - mmput(mm); > - return NULL; > } > > static int proc_pid_cmdline(struct task_struct *task, char * buffer) > > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html