Daniel P. Berrangé
Committed by Eric Blake

io: return 0 for EOF in TLS session read after shutdown

GNUTLS takes a paranoid approach when seeing 0 bytes returned by the
underlying OS read() function. It will consider this an error and
return GNUTLS_E_PREMATURE_TERMINATION instead of propagating the 0
return value. It expects apps to arrange for clean termination at
the protocol level and not rely on seeing EOF from a read call to
detect shutdown. This is to harden apps against a malicious 3rd party
causing termination of the sockets layer.

This is unhelpful for the QEMU NBD code which does have a clean
protocol level shutdown, but still relies on seeing 0 from the I/O
channel read in the coroutine handling incoming replies.

The upshot is that when using a plain NBD connection shutdown is
silent, but when using TLS, the client spams the console with

  Cannot read from TLS channel: Broken pipe

The NBD connection has, however, called qio_channel_shutdown()
at this point to indicate that it is done with I/O. This gives
the opportunity to optimize the code such that when the channel
has been shutdown in the read direction, the error code
GNUTLS_E_PREMATURE_TERMINATION gets turned into a '0' return
instead of an error.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20181119134228.11031-1-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
... ... @@ -473,6 +473,9 @@ qcrypto_tls_session_read(QCryptoTLSSession *session,
case GNUTLS_E_INTERRUPTED:
errno = EINTR;
break;
case GNUTLS_E_PREMATURE_TERMINATION:
errno = ECONNABORTED;
break;
default:
errno = EIO;
break;
... ...
... ... @@ -48,6 +48,7 @@ struct QIOChannelTLS {
QIOChannel parent;
QIOChannel *master;
QCryptoTLSSession *session;
QIOChannelShutdown shutdown;
};
/**
... ...
... ... @@ -51,9 +51,9 @@ enum QIOChannelFeature {
typedef enum QIOChannelShutdown QIOChannelShutdown;
enum QIOChannelShutdown {
QIO_CHANNEL_SHUTDOWN_BOTH,
QIO_CHANNEL_SHUTDOWN_READ,
QIO_CHANNEL_SHUTDOWN_WRITE,
QIO_CHANNEL_SHUTDOWN_READ = 1,
QIO_CHANNEL_SHUTDOWN_WRITE = 2,
QIO_CHANNEL_SHUTDOWN_BOTH = 3,
};
typedef gboolean (*QIOChannelFunc)(QIOChannel *ioc,
... ...
... ... @@ -275,6 +275,9 @@ static ssize_t qio_channel_tls_readv(QIOChannel *ioc,
} else {
return QIO_CHANNEL_ERR_BLOCK;
}
} else if (errno == ECONNABORTED &&
(tioc->shutdown & QIO_CHANNEL_SHUTDOWN_READ)) {
return 0;
}
error_setg_errno(errp, errno,
... ... @@ -357,6 +360,8 @@ static int qio_channel_tls_shutdown(QIOChannel *ioc,
{
QIOChannelTLS *tioc = QIO_CHANNEL_TLS(ioc);
tioc->shutdown |= how;
return qio_channel_shutdown(tioc->master, how, errp);
}
... ...