Re: [Qemu-devel] [PATCH 3/3] nbd: Reject unknown request flags

[Paolo Bonzini <pbonzini@redhat.com>]

On 31/03/2016 23:20, Eric Blake wrote:
> The NBD protocol says that clients should not send a command flag
> that has not been negotiated (whether by the client requesting an
> option during a handshake, or because we advertise support for the
> flag in response to NBD_OPT_EXPORT_NAME), and that servers should
> reject invalid flags with EINVAL.  We were silently ignoring the
> flags instead.  The client can't rely on our behavior, since it is
> their fault for passing the bad flag in the first place, but it's
> better to be robust up front than to possibly behave differently
> than the client was expecting with the attempted flag.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  nbd/server.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/nbd/server.c b/nbd/server.c
> index a590773..31bd9c5 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -974,6 +974,10 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
>          goto out;
>      }
> 
> +    if (request->flags & ~NBD_CMD_FLAG_FUA) {
> +        LOG("unsupported flags (got 0x%x)", request->flags);
> +        return -EINVAL;
> +    }
>      if ((request->from + request->len) < request->from) {
>          LOG("integer overflow detected! "
>              "you're probably being attacked");
> 

Queued for 2.6.

Paolo