Messages in this thread Patch in this message | | | Date | Tue, 20 Mar 2012 10:55:43 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [patch 1/2] c/r: prctl: Add ability to set new mm_struct::exe_file |
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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 <gorcunov@openvz.org> 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 <gorcunov@openvz.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> CC: Pavel Emelyanov <xemul@parallels.com> CC: Kees Cook <keescook@chromium.org> CC: Tejun Heo <tj@kernel.org> CC: Matt Helsley <matthltc@us.ibm.com> CC: richard -rw- weinberger <richard.weinberger@gmail.com> --- 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 <linux/personality.h> #include <linux/ptrace.h> #include <linux/fs_struct.h> +#include <linux/file.h> +#include <linux/mount.h> #include <linux/gfp.h> #include <linux/syscore_ops.h> #include <linux/version.h> @@ -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;
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