Re: [Qemu-devel] [PATCH v2 2/1 for-2.6] nbd: Don't kill server when client requests unknown option

[Eric Blake]

Adding qemu-stable; this fix needs to be backported to 2.5.x stable
series (in the file ./nbd.c at the time), if we want to be able to allow
a 2.7 client to connect to a 2.5 server.

On 04/06/2016 04:48 PM, Eric Blake wrote:
> nbd-server.c currently fails to handle unsupported options properly.
> If during option haggling the client sends an unknown request, the
> server kills the connection instead of letting the client try to
> fall back to something older.  This is precisely what advertising
> NBD_FLAG_FIXED_NEWSTYLE was supposed to fix.
> 
> Signed-off-by: Eric Blake <address@hidden>
> ---
> 
> Turns out our server has a very similar bug to the client.
> If desired, I can spin a v3 that moves the hunk in nbd/client.c
> to the previous patch.
> 
>  nbd/client.c | 2 ++
>  nbd/server.c | 5 ++++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/nbd/client.c b/nbd/client.c
> index 67116b9..fc382c5 100644
> --- a/nbd/client.c
> +++ b/nbd/client.c
> @@ -109,6 +109,8 @@ static int nbd_handle_reply_err(QIOChannel *ioc, uint32_t 
> opt, uint32_t type,
> 
>      switch (type) {
>      case NBD_REP_ERR_UNSUP:
> +        TRACE("server doesn't understand request %d, attempting fallback",
> +              opt);
>          result = 0;
>          goto cleanup;
> 
> diff --git a/nbd/server.c b/nbd/server.c
> index b95571b..7843584 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -482,9 +482,12 @@ static int nbd_negotiate_options(NBDClient *client)
>                  return -EINVAL;
>              default:
>                  TRACE("Unsupported option 0x%x", clientflags);
> +                if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
> +                    return -EIO;
> +                }
>                  nbd_negotiate_send_rep(client->ioc, NBD_REP_ERR_UNSUP,
>                                         clientflags);
> -                return -EINVAL;
> +                break;
>              }
>          } else {
>              /*
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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