Libguestfs - Aug 2013 - Re: missing chdir before chroot in guestfsd

daemon.c does just a chroot, without chdir. The result is that pwd does not
work correctly (it causes fs/dcache.c:prepend_unreachable() to add the
unreachable string). A workaround is to add "cd /" before each sh
command.
><fs> mount /dev/sda2 /
><fs> sh "cd / ; chroot / ; /bin/pwd"
/
><fs> sh "/bin/pwd"
(unreachable)/
><fs> sh "cd / ; /bin/pwd"
/

This untested change may fix it.

==================--- libguestfs-1.20.10.orig/daemon/guestfsd.c
+++ libguestfs-1.20.10/daemon/guestfsd.c
@@ -879,7 +879,11 @@ commandrvf (char **stdoutput, char **std
       close (stdin_fd[PIPE_READ]);
       close (stdin_fd[PIPE_WRITE]);
 
-      if (chroot (sysroot) == -1) {
+      if (chdir (sysroot) == -1) {
+        perror ("chdir");
+        _exit (EXIT_FAILURE);
+      }
+      if (chroot (".") == -1) {
         perror ("chroot");
         _exit (EXIT_FAILURE);
       }
 
Olaf

On Sun, Aug 18, Olaf Hering wrote:
> 
> daemon.c does just a chroot, without chdir. The result is that pwd does not
> work correctly (it causes fs/dcache.c:prepend_unreachable() to add the
> unreachable string). A workaround is to add "cd /" before each sh
command.
> 
> ><fs> mount /dev/sda2 /
> ><fs> sh "cd / ; chroot / ; /bin/pwd"
> /
> 
> ><fs> sh "/bin/pwd"
> (unreachable)/
> 
> ><fs> sh "cd / ; /bin/pwd"
> /

This change fixes the "pwd" output for me.

guestfish add-drive /dev/shm/olaf/vdisk-sles11sp2_full_fate310510-disk0 : launch
: mount /dev/sda2 / : sh pwd : quit
/


Olaf

---
 daemon/command.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

Index: libguestfs-1.20.10/daemon/command.c
==================================================================---
libguestfs-1.20.10.orig/daemon/command.c
+++ libguestfs-1.20.10/daemon/command.c
@@ -21,6 +21,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 
 #include "guestfs_protocol.h"
 #include "daemon.h"
@@ -46,6 +49,7 @@ do_command (char *const *argv)
   CLEANUP_FREE char *sysroot_dev = NULL, *sysroot_dev_pts = NULL,
     *sysroot_proc = NULL, *sysroot_selinux = NULL, *sysroot_sys = NULL;
   int dev_ok, dev_pts_ok, proc_ok, sys_ok;
+  int cwd_fd;
 
   /* We need a root filesystem mounted to do this. */
   NEED_ROOT (, return NULL);
@@ -89,8 +93,15 @@ do_command (char *const *argv)
   r = command (NULL, NULL, str_mount, "--bind", "/sys",
sysroot_sys, NULL);
   sys_ok = r != -1;
 
+  cwd_fd = open(".", O_DIRECTORY);
   CHROOT_IN;
+  if (cwd_fd >= 0)
+	chdir("/");
   r = commandv (&out, &err, (const char * const *) argv);
+  if (cwd_fd >= 0) {
+	  fchdir(cwd_fd);
+	  close(cwd_fd);
+  }
   CHROOT_OUT;
 
   if (sys_ok) umount_ignore_fail (sysroot_sys);

On Sun, Aug 18, 2013 at 02:29:15PM +0200, Olaf Hering
wrote:
> 
> daemon.c does just a chroot, without chdir. The result is that pwd does not
> work correctly (it causes fs/dcache.c:prepend_unreachable() to add the
> unreachable string). A workaround is to add "cd /" before each sh
command.
> 
> ><fs> mount /dev/sda2 /
> ><fs> sh "cd / ; chroot / ; /bin/pwd"
> /
> 
> ><fs> sh "/bin/pwd"
> (unreachable)/
> 
> ><fs> sh "cd / ; /bin/pwd"
> /
> 
> This untested change may fix it.
> 
> ==================> --- libguestfs-1.20.10.orig/daemon/guestfsd.c
> +++ libguestfs-1.20.10/daemon/guestfsd.c
> @@ -879,7 +879,11 @@ commandrvf (char **stdoutput, char **std
>        close (stdin_fd[PIPE_READ]);
>        close (stdin_fd[PIPE_WRITE]);
>  
> -      if (chroot (sysroot) == -1) {
> +      if (chdir (sysroot) == -1) {
> +        perror ("chdir");
> +        _exit (EXIT_FAILURE);
> +      }
> +      if (chroot (".") == -1) {
>          perror ("chroot");
>          _exit (EXIT_FAILURE);
>        }
If you look at the upstream code, this has been fixed, or at
least, the code is quite different.  See:

commit 2aa731e7c441581f0d72bcd06e9431b92931466a
Author: Matthew Booth <mbooth@redhat.com>
Date:   Thu Dec 13 15:22:39 2012 +0000

    daemon: Remove redundant fork in commandrvf

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v

On Mon, Aug 19, Richard W.M. Jones wrote:
> If you look at the upstream code, this has been fixed, or at
> least, the code is quite different.  See:
> 
> commit 2aa731e7c441581f0d72bcd06e9431b92931466a
It does not happen with 1.23.17. Thanks.

Olaf