From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755550Ab2CTGzu (ORCPT ); Tue, 20 Mar 2012 02:55:50 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:35958 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754808Ab2CTGzs (ORCPT ); Tue, 20 Mar 2012 02:55:48 -0400 Date: Tue, 20 Mar 2012 10:55:43 +0400 From: Cyrill Gorcunov To: Andrew Morton Cc: richard -rw- weinberger , LKML , Oleg Nesterov , KOSAKI Motohiro , Pavel Emelyanov , Kees Cook , Tejun Heo , Matt Helsley Subject: Re: [patch 1/2] c/r: prctl: Add ability to set new mm_struct::exe_file Message-ID: <20120320065543.GB14269@moon> References: <20120316205556.595309230@openvz.org> <20120316210343.925446961@openvz.org> <20120319151507.93bab32a.akpm@linux-foundation.org> <20120319223941.GJ19594@moon> <20120319154649.0687f545.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120319154649.0687f545.akpm@linux-foundation.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 19, 2012 at 03:46:49PM -0700, Andrew Morton wrote: > > >> > > >> What is this mysterious "security reason"? > > >> > > > > > > Oh, sorry I should have included Matt's comment here > > Please send a patch with the updated changelog and improved comment? > Andrew, take a look please, will the changelog and comments look better? Cyrill --- From: Cyrill Gorcunov Subject: c/r: prctl: add ability to set new mm_struct::exe_file When we do restore we would like to have a way to setup a former mm_struct::exe_file so that /proc/pid/exe would point to the original executable file a process had at checkpoint time. For this the PR_SET_MM_EXE_FILE code is introduced. This option takes a file descriptor which will be set as a source for new /proc/$pid/exe symlink. Note it allows to change /proc/$pid/exe iif there are no VM_EXECUTABLE vmas present for current process, simply because this feature is a special to C/R and mm::num_exe_file_vmas become meaningless after that. To minimize the amount of transition the /proc/pid/exe symlink might have, this feature is implemented in one-shot manner. Thus once changed the symlink can't be changed again. This should help sysadmins to monitor the symlinks over all process running in a system. In particular one could make a snapshot of processes and ring alarm if there unexpected changes of /proc/pid/exe's in a system. Note -- this feature is available iif CONFIG_CHECKPOINT_RESTORE is set and the caller must have CAP_SYS_RESOURCE capability granted, otherwise the request to change symlink will be rejected. Signed-off-by: Cyrill Gorcunov Reviewed-by: Oleg Nesterov CC: KOSAKI Motohiro CC: Pavel Emelyanov CC: Kees Cook CC: Tejun Heo CC: Matt Helsley CC: richard -rw- weinberger --- include/linux/prctl.h | 1 kernel/sys.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 57 insertions(+) Index: linux-2.6.git/include/linux/prctl.h =================================================================== --- linux-2.6.git.orig/include/linux/prctl.h +++ linux-2.6.git/include/linux/prctl.h @@ -118,5 +118,6 @@ # define PR_SET_MM_ENV_START 10 # define PR_SET_MM_ENV_END 11 # define PR_SET_MM_AUXV 12 +# define PR_SET_MM_EXE_FILE 13 #endif /* _LINUX_PRCTL_H */ Index: linux-2.6.git/kernel/sys.c =================================================================== --- linux-2.6.git.orig/kernel/sys.c +++ linux-2.6.git/kernel/sys.c @@ -36,6 +36,8 @@ #include #include #include +#include +#include #include #include #include @@ -1701,6 +1703,57 @@ static bool vma_flags_mismatch(struct vm (vma->vm_flags & banned); } +static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) +{ + struct file *exe_file; + struct dentry *dentry; + int err; + + /* + * Setting new mm::exe_file is only allowed when no VM_EXECUTABLE vma's + * remain. So perform a quick test first. + */ + if (mm->num_exe_file_vmas) + return -EBUSY; + + exe_file = fget(fd); + if (!exe_file) + return -EBADF; + + dentry = exe_file->f_path.dentry; + + /* + * Because the original mm->exe_file points to executable file, make + * sure that this one is executable as well, to avoid breaking an + * overall picture. + */ + err = -EACCES; + if (!S_ISREG(dentry->d_inode->i_mode) || + exe_file->f_path.mnt->mnt_flags & MNT_NOEXEC) + goto exit; + + err = inode_permission(dentry->d_inode, MAY_EXEC); + if (err) + goto exit; + + /* + * The symlink can be changed only once, just to disallow arbitrary + * transitions malicious software might bring in. This means one + * could make a snapshot over all processes running and monitor + * /proc/pid/exe changes to notice unusual activity if needed. + */ + down_write(&mm->mmap_sem); + if (likely(!mm->exe_file)) + set_mm_exe_file(mm, exe_file); + else + err = -EBUSY; + up_write(&mm->mmap_sem); + +exit: + fput(exe_file); + return err; +} + static int prctl_set_mm(int opt, unsigned long addr, unsigned long arg4, unsigned long arg5) { @@ -1715,6 +1768,9 @@ static int prctl_set_mm(int opt, unsigne if (!capable(CAP_SYS_RESOURCE)) return -EPERM; + if (opt == PR_SET_MM_EXE_FILE) + return prctl_set_mm_exe_file(mm, (unsigned int)addr); + if (addr >= TASK_SIZE) return -EINVAL;