chroot: Change directory to '/' after calling os.chroot()

This fixes https://github.com/CodethinkLabs/sandboxlib/issues/6
where passing a relative path for 'cwd' caused an error. I had assumed
that os.chroot() reset the current working directory itself, since
the `chroot` program does, but apparently not.

1 files changed, 3 insertions, 0 deletions

diff --git a/sandboxlib/chroot.py b/sandboxlib/chroot.py
index 6adaa06..c0f662b 100644
--- a/sandboxlib/chroot.py
+++ b/sandboxlib/chroot.py
@@ -167,6 +167,9 @@ def run_command_in_chroot(pipe, stdout, stderr, extra_mounts, chroot_path,
         except OSError as e:
             raise RuntimeError("Unable to chroot: %s" % e)
 
+        # This is important in case 'cwd' is a relative path.
+        os.chdir('/')
+
         if cwd is not None:
             try:
                 os.chdir(cwd)