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' with the main socket being matched more
strictly. 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.eb...@proxmox.com>
---

Changes in v3:
* Match main socket address more strictly as suggested by Fabian.

 PVE/QemuMigrate.pm | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/PVE/QemuMigrate.pm b/PVE/QemuMigrate.pm
index e71face4..6591f3f7 100644
--- a/PVE/QemuMigrate.pm
+++ b/PVE/QemuMigrate.pm
@@ -1095,7 +1095,9 @@ 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) = $tunnel_info->{addr} =~ 
m|^(/run/qemu-server/\d+\.migrate)$|
+           or die "unexpected socket address '$tunnel_info->{addr}'\n";
        my $local_socket = $remote_socket;
        $local_socket =~ s/$remote_vmid/$vmid/g;
        $tunnel_info->{addr} = $local_socket;
@@ -1104,6 +1106,9 @@ sub phase2 {
        PVE::Tunnel::forward_unix_socket($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



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