[pve-devel] [PATCH storage] rbd: alloc image: fix #3970 avoid ambiguous rbd path

[Aaron Lauterer]

If two RBD storages use the same pool, but connect to different
clusters, we cannot say to which cluster the mapped RBD image belongs to
if krbd is used. To avoid potential data loss, we need to verify that no
other storage is configured that could have a volume mapped under the
same path before we allocate the image.

The ambiguous mapping is in
/dev/rbd/<pool>/<ns>/<image> where the namespace <ns> is optional.

Once we can tell the clusters apart in the mapping, we can remove these
checks again.

See bug #3969 for more information on the root cause.

Signed-off-by: Aaron Lauterer <a.lauterer at proxmox.com>
---
changes since RFC:

* moved check to pve-storage since containers and VMs both have issues
  not just on a move or clone of the image, but also when creating a new
  volume
* reworked the checks, instead of large if conditions, we use
  PVE::Tools::safe_compare with comparison functions
* normalize monhost list to match correctly if the list is in different
  order
* add storage name to error message that triggered the checks
* ignore disabled storages

 PVE/Storage/RBDPlugin.pm | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/PVE/Storage/RBDPlugin.pm b/PVE/Storage/RBDPlugin.pm
index e287e28..a9dbf5e 100644
--- a/PVE/Storage/RBDPlugin.pm
+++ b/PVE/Storage/RBDPlugin.pm
@@ -516,6 +516,40 @@ sub alloc_image {
     die "illegal name '$name' - should be 'vm-$vmid-*'\n"
 	if  $name && $name !~ m/^vm-$vmid-/;
 
+    # check if another rbd storage with the same pool name but different
+    # cluster exists. If so, allocating a new volume can potentially be
+    # dangerous because the RBD mapping, exposes it in an ambiguous way under
+    # /dev/rbd/<pool>/<ns>/<image>. Without any information to which cluster it
+    # belongs, we cannot clearly determine which image we access and
+    # potentially use the wrong one. See
+    # https://bugzilla.proxmox.com/show_bug.cgi?id=3969 and
+    # https://bugzilla.proxmox.com/show_bug.cgi?id=3970
+    # TODO: remove these checks once #3969 is fixed and we can clearly tell to
+    # which cluster an image belongs to
+    my $storecfg = PVE::Storage::config();
+    foreach my $store  (keys %{$storecfg->{ids}}) {
+	next if $store eq $storeid;
+
+	my $checked_scfg = $storecfg->{ids}->{$store};
+
+	next if $checked_scfg->{type} ne 'rbd';
+	next if $checked_scfg->{disable};
+	next if $scfg->{pool} ne $checked_scfg->{pool};
+
+	my $normalize_mons = sub { return join('/', sort( PVE::Tools::split_list(' ', shift))) };
+	my $cmp_mons = sub { $normalize_mons->($_[0]) cmp $normalize_mons->($_[1]) };
+	my $cmp = sub { $_[0] cmp $_[1] };
+
+	# internal and internal, or external and external with identical monitors
+	# => same cluster
+	next if PVE::Tools::safe_compare($scfg->{monhost}, $checked_scfg->{monhost}, $cmp_mons) == 0;
+
+	# different namespaces => no clash possible
+	next if !PVE::Tools::safe_compare($scfg->{namespace}, $checked_scfg->{namespace}, $cmp) == 0;
+
+	die "Other storage found which would lead to ambiguous mappings: '$store'\n";
+    }
+
     $name = $class->find_free_diskname($storeid, $scfg, $vmid) if !$name;
 
     my @options = (
-- 
2.30.2