From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757939Ab2CHVsZ (ORCPT ); Thu, 8 Mar 2012 16:48:25 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:48134 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757639Ab2CHVsX (ORCPT ); Thu, 8 Mar 2012 16:48:23 -0500 Date: Fri, 9 Mar 2012 01:48:17 +0400 From: Cyrill Gorcunov To: Oleg Nesterov Cc: Matt Helsley , KOSAKI Motohiro , Pavel Emelyanov , Kees Cook , Tejun Heo , Andrew Morton , LKML Subject: Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3 Message-ID: <20120308214817.GO21812@moon> References: <20120308165112.GF21812@moon> <20120308182623.GA17221@redhat.com> <20120308190303.GG21812@moon> <20120308190534.GA19827@redhat.com> <20120308192504.GH21812@moon> <20120308192559.GA20782@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120308192559.GA20782@redhat.com> 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 Thu, Mar 08, 2012 at 08:25:59PM +0100, Oleg Nesterov wrote: ... > > But please-please document the new special case in the changelog. > Oleg, will the following change log sound more or less fine? Cyrill --- From: Cyrill Gorcunov Subject: c/r: prctl: Add ability to set new mm_struct::exe_file v4 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. This feature is available iif CONFIG_CHECKPOINT_RESTORE is set. Signed-off-by: Cyrill Gorcunov CC: Oleg Nesterov CC: KOSAKI Motohiro CC: Pavel Emelyanov CC: Kees Cook CC: Tejun Heo CC: Matt Helsley --- include/linux/prctl.h | 1 kernel/sys.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 55 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 +1703,55 @@ 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; + + 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 + * this one is executable as well to not + * break 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; + + /* + * Setting new mm::exe_file is only allowed + * when no executable VMAs left. This is + * special C/R case when a restored program + * need to change own /proc/$pid/exe symlink. + * After this call mm::num_exe_file_vmas become + * meaningless. + */ + down_write(&mm->mmap_sem); + if (mm->num_exe_file_vmas == 0) { + set_mm_exe_file(mm, exe_file); + exe_file = NULL; + } else + err = -EBUSY; + up_write(&mm->mmap_sem); + +exit: + if (exe_file) + fput(exe_file); + return err; +} + static int prctl_set_mm(int opt, unsigned long addr, unsigned long arg4, unsigned long arg5) { @@ -1715,6 +1766,9 @@ 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;