tools/virtiofsd: Add fstatfs64 syscall to the seccomp allowlist

The virtiofsd currently crashes on s390x when doing something like
this in the guest:

 mkdir -p /mnt/myfs
 mount -t virtiofs myfs /mnt/myfs
 touch /mnt/myfs/foo.txt
 stat -f /mnt/myfs/foo.txt

The problem is that the fstatfs64 syscall is called in this case
from the virtiofsd. We have to put it on the seccomp allowlist to
avoid that the daemon gets killed in this case.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2001728
Suggested-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210914123214.181885-1-thuth@redhat.com>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tools/virtiofsd/passthrough_seccomp.c

@@ -51,6 +51,7 @@ static const int syscall_allowlist[] = {
     SCMP_SYS(fsetxattr),
     SCMP_SYS(fstat),
     SCMP_SYS(fstatfs),
+    SCMP_SYS(fstatfs64),
     SCMP_SYS(fsync),
     SCMP_SYS(ftruncate),
     SCMP_SYS(futex),