[Libguestfs] [PATCH libnbd 2/2] lib/crypto.c: Ignore TLS premature termination after write shutdown

[Laszlo Ersek]

On 07/27/22 18:30, Richard W.M. Jones wrote:
> qemu-nbd doesn't call gnutls_bye to cleanly shut down the connection
> after we send NBD_CMD_DISC.  When copying from a qemu-nbd server (or
> any operation which calls nbd_shutdown) you will see errors like this:
> 
>   $ nbdcopy nbds://foo?tls-certificates=/var/tmp/pki null:
>   nbds://foo?tls-certificates=/var/tmp/pki: nbd_shutdown: gnutls_record_recv: The TLS connection was non-properly terminated.
> 
> Relatedly you may also see:
> 
>   nbd_shutdown: gnutls_record_recv: Error in the pull function.
> 
> This commit suppresses the error in the case where we know that we
> have shut down writes (which happens after NBD_CMD_DISC has been sent
> on the wire).
> ---
>  interop/interop.c |  9 ---------
>  lib/crypto.c      | 17 +++++++++++++++++
>  lib/internal.h    |  1 +
>  3 files changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/interop/interop.c b/interop/interop.c
> index 036545bd82..cce9407aa1 100644
> --- a/interop/interop.c
> +++ b/interop/interop.c
> @@ -226,19 +226,10 @@ main (int argc, char *argv[])
>  
>    /* XXX In future test more operations here. */
>  
> -#if !TLS
> -  /* XXX qemu doesn't shut down the connection nicely (using
> -   * gnutls_bye) and because of this the following call will fail
> -   * with:
> -   *
> -   * nbd_shutdown: gnutls_record_recv: The TLS connection was
> -   * non-properly terminated.
> -   */
>    if (nbd_shutdown (nbd, 0) == -1) {
>      fprintf (stderr, "%s\n", nbd_get_error ());
>      exit (EXIT_FAILURE);
>    }
> -#endif
>  
>    nbd_close (nbd);
>  
> diff --git a/lib/crypto.c b/lib/crypto.c
> index ffba4bda9b..a2832b1585 100644
> --- a/lib/crypto.c
> +++ b/lib/crypto.c
> @@ -189,6 +189,22 @@ tls_recv (struct nbd_handle *h, struct socket *sock, void *buf, size_t len)
>        errno = EAGAIN;
>        return -1;
>      }
> +    if (h->tls_shut_writes &&
> +        (r == GNUTLS_E_PULL_ERROR || r == GNUTLS_E_PREMATURE_TERMINATION)) {
> +      /* qemu-nbd doesn't call gnutls_bye to cleanly shut down the
> +       * connection after we send NBD_CMD_DISC, instead it simply
> +       * closes the connection.  On the client side we see
> +       * "gnutls_record_recv: The TLS connection was non-properly
> +       * terminated" or "gnutls_record_recv: Error in the pull
> +       * function.".
> +       *
> +       * If we see these errors after we shut down the write side
> +       * (h->tls_shut_writes), which happens after we have sent
> +       * NBD_CMD_DISC on the wire, downgrade them to a debug message.
> +       */
> +      debug (h, "gnutls_record_recv: %s", gnutls_strerror (r));
> +      return 0; /* EOF */
> +    }
>      set_error (0, "gnutls_record_recv: %s", gnutls_strerror (r));
>      errno = EIO;
>      return -1;
> @@ -236,6 +252,7 @@ tls_shut_writes (struct nbd_handle *h, struct socket *sock)
>      return false;
>    if (r != 0)
>      debug (h, "ignoring gnutls_bye failure: %s", gnutls_strerror (r));
> +  h->tls_shut_writes = true;
>    return sock->u.tls.oldsock->ops->shut_writes (h, sock->u.tls.oldsock);
>  }
>  
> diff --git a/lib/internal.h b/lib/internal.h
> index 4121a5cdaa..8dbe2e4568 100644
> --- a/lib/internal.h
> +++ b/lib/internal.h
> @@ -307,6 +307,7 @@ struct nbd_handle {
>    struct command *reply_cmd;
>  
>    bool disconnect_request;      /* True if we've queued NBD_CMD_DISC */
> +  bool tls_shut_writes;         /* Used by lib/crypto.c to track disconnect. */
>  };
>  
>  struct meta_context {
> 

Looks reasonable.

Acked-by: Laszlo Ersek <lersek at redhat.com>