Bug#829125: schroot: schroot doesn't clean up its bind mounts if used concurrently

[Dima Kogan]

Hi. I just looked into this a bit more.

First off, I think we should unmount as many things as we can, instead
of giving up at the first failure. This is the first patch that is
attached.

For the bigger issue here, you are right. Systemd is at fault:

  https://bugs.freedesktop.org/show_bug.cgi?id=81695

I won't claim to fully understand what's going on here, but the attached
second patch fixes the problem.

The duplicate mounts are created (presumably inside the kernel) without
extra mount() syscalls. Also for some reason zsh tickles this behavior,
but bash does not. I have several chroots that I use constantly with
zsh, and so I hit this issue very often. It would be great if some sort
of fix was deployed.

Sorry I couldn't provide more insight.

dima.




>From b85966683ae3b216333b2691fbd2ab84ab4e3ad4 Mon Sep 17 00:00:00 2001
From: Dima Kogan <d...@secretsauce.net>
Date: Sat, 2 Jul 2016 14:56:15 -0700
Subject: [PATCH] Unmount everything that we can, instead of giving up at the
 first failure

---
 etc/setup.d/10mount | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/etc/setup.d/10mount b/etc/setup.d/10mount
index 27c18d0..bbd631c 100755
--- a/etc/setup.d/10mount
+++ b/etc/setup.d/10mount
@@ -93,12 +93,16 @@ do_umount_all()
 
         ( flock 9
             mounts="$("$LIBEXEC_DIR/schroot-listmounts" -m "$1")"
+            anyfailed=""
             if [ "x$mounts" != 'x' ]; then
                 echo "$mounts" |
                 while read mountloc; do
                     info "Unmounting $mountloc"
-                    umount "$mountloc" || exit 1
-                done || exit 1
+                    umount "$mountloc" || anyfailed="yes"
+                done
+
+                [ -n "$anyfailed" ] && exit 1
+                true
             fi
         ) 9>"/var/lock/schroot/umount"
     else
-- 
2.8.0.rc3


>From 94494132d8bb3b95fa22dd82f9d974fbe8f5b2e4 Mon Sep 17 00:00:00 2001
From: Dima Kogan <d...@secretsauce.net>
Date: Sat, 2 Jul 2016 19:38:56 -0700
Subject: [PATCH 2/2] Disabled bind mount propagation

See

  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=829125
  https://bugs.freedesktop.org/show_bug.cgi?id=81695
---
 bin/schroot-mount/schroot-mount-main.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/bin/schroot-mount/schroot-mount-main.cc b/bin/schroot-mount/schroot-mount-main.cc
index 327f5ed..b92f330 100644
--- a/bin/schroot-mount/schroot-mount-main.cc
+++ b/bin/schroot-mount/schroot-mount-main.cc
@@ -200,6 +200,7 @@ main::action_mount ()
         {
           sbuild::string_list command;
           command.push_back("/bin/mount");
+          command.push_back("--make-rslave");
           if (opts->verbose)
             command.push_back("-v");
           command.push_back("-t");
-- 
2.8.0.rc3