[debian-mysql] Bug#829491: mariadb-server-10.0: Removes lost+found directory if purged, /var/lib/mysql is a mountpoint with an ext4 filesystem, and user requests to remove all databases

[Axel Beckert]

Control: tag -1 + patch

Hi Otto,

Otto Kekäläinen wrote:
> Thanks for your report. The problem is that the purge section in the
> postrm script does a simple rm, which works OK if the directory is a
> normal directory, but not if it is a mountpoint. The postrm script
> does not have any kind of mountpoint detection or conditional
> handling for that scenario.
> 
> Would you want to give it a try and produce a patch?

Yes:

diff --git a/debian/mariadb-server-10.0.postrm b/debian/mariadb-server-10.0.postrm
index 1f7034c..43b68a0 100644
--- a/debian/mariadb-server-10.0.postrm
+++ b/debian/mariadb-server-10.0.postrm
@@ -56,7 +56,17 @@ if [ "$1" = "purge" -a ! \( -x /usr/sbin/mysqld -o -L /usr/sbin/mysqld \) ]; the
     # never remove the debian.cnf when the databases are still existing
     # else we ran into big trouble on the next install!
     rm -f /etc/mysql/debian.cnf
-    rm -rf /var/lib/mysql
+    # Remove all contents from /var/lib/mysql except if it's a
+    # directory with file system data. See #829491 for details and
+    # #608938 for potential mysql-server leftovers which erroneously
+    # had been renamed.
+    find /var/lib/mysql -mindepth 1 \
+         -not -path '*/lost+found/*'     -not -name 'lost+found' \
+         -not -path '*/lost at 002bfound/*' -not -name 'lost at 002bfound' \
+         -delete
+    # "|| true" still needed as rmdir still exits with non-zero if
+    # /var/lib/mysql is a mount point
+    rmdir --ignore-fail-on-non-empty /var/lib/mysql || true
     rm -rf /var/run/mysqld # this directory is created by the init script, don't leave behind
     userdel mysql || true
   fi

I tried to

* not use the existence of lost+found as indicator for /var/lib/mysql
  being a mount point.
* to also keep erroneously renamed lost+found directories as they
  might continue to exist after a switch from MySQL to MariaDB.

> If you provide a patch, I am happy to review it and help with testing.
> As this is only some scripting, you don't need to spend time building
> MariaDB at all, just unpack the deb and hack on the postrm script.

As you suggested I haven't tested the whole patch as you suggested,
but at least each line separately -- with quickly generated dummy
files and directories only, though. (That way I noticed that
--ignore-fail-on-non-empty doesn't suffice for mount points.) Hope,
that suffices.

		Regards, Axel
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