[pve-devel] [PATCH v2 qemu-server] remote migration: fix online migration via API clients

[Fiona Ebner]

As reported in the community forum [0], when a remote migration
request comes in via an API client, the -T flag for Perl is set, so an
insecure dependency in a call like unlink() in forward_unix_socket()
will fail with:

> failed to write forwarding command - Insecure dependency in unlink while running with -T switch

To fix it, untaint the problematic socket addresses coming from the
remote side. Require that all sockets are below '/run/qemu-server/'
and end with '.migrate'. This allows extensions in the future while
still being quite strict.

[0]: https://forum.proxmox.com/threads/123048/post-691958

Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---

Changes in v2:
* rule out '../' in path

 PVE/QemuMigrate.pm | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/PVE/QemuMigrate.pm b/PVE/QemuMigrate.pm
index e71face4..d31589e7 100644
--- a/PVE/QemuMigrate.pm
+++ b/PVE/QemuMigrate.pm
@@ -1095,7 +1095,10 @@ sub phase2 {
 	die "only UNIX sockets are supported for remote migration\n"
 	    if $tunnel_info->{proto} ne 'unix';
 
-	my $remote_socket = $tunnel_info->{addr};
+	# untaint
+	my ($remote_socket) =
+	    $tunnel_info->{addr} =~ m|^(/run/qemu-server/(?:(?!\.\./).)+\.migrate)$|;
+	die "unexpected socket address '$tunnel_info->{addr}'\n" if !$remote_socket;
 	my $local_socket = $remote_socket;
 	$local_socket =~ s/$remote_vmid/$vmid/g;
 	$tunnel_info->{addr} = $local_socket;
@@ -1104,6 +1107,9 @@ sub phase2 {
 	PVE::Tunnel::forward_unix_socket($self->{tunnel}, $local_socket, $remote_socket);
 
 	foreach my $remote_socket (@{$tunnel_info->{unix_sockets}}) {
+	    # untaint
+	    ($remote_socket) = $remote_socket =~ m|^(/run/qemu-server/(?:(?!\.\./).)+\.migrate)$|
+		or die "unexpected socket address '$remote_socket'\n";
 	    my $local_socket = $remote_socket;
 	    $local_socket =~ s/$remote_vmid/$vmid/g;
 	    next if $self->{tunnel}->{forwarded}->{$local_socket};
-- 
2.39.2