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Revision fdad35ef6c5839d50dfc14073364ac893afebc30 authored by Eric Blake on 22 November 2017, 22:25:16 UTC, committed by Eric Blake on 28 November 2017, 12:42:26 UTC 
nbd/server: CVE-2017-15119 Reject options larger than 32M
 
The NBD spec gives us permission to abruptly disconnect on clients
that send outrageously large option requests, rather than having
to spend the time reading to the end of the option.  No real
option request requires that much data anyways; and meanwhile, we
already have the practice of abruptly dropping the connection on
any client that sends NBD_CMD_WRITE with a payload larger than 32M.

For comparison, nbdkit drops the connection on any request with
more than 4096 bytes; however, that limit is probably too low
(as the NBD spec states an export name can theoretically be up
to 4096 bytes, which means a valid NBD_OPT_INFO could be even
longer) - even if qemu doesn't permit exports longer than 256
bytes.

It could be argued that a malicious client trying to get us to
read nearly 4G of data on a bad request is a form of denial of
service.  In particular, if the server requires TLS, but a client
that does not know the TLS credentials sends any option (other
than NBD_OPT_STARTTLS or NBD_OPT_EXPORT_NAME) with a stated
payload of nearly 4G, then the server was keeping the connection
alive trying to read all the payload, tying up resources that it
would rather be spending on a client that can get past the TLS
handshake.  Hence, this warranted a CVE.

Present since at least 2.5 when handling known options, and made
worse in 2.6 when fixing support for NBD_FLAG_C_FIXED_NEWSTYLE
to handle unknown options.

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
1 parent c7e1f82
Raw File
ivgen.c 
/*
 * QEMU Crypto block IV generator
 *
 * Copyright (c) 2015-2016 Red Hat, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 *
 */

#include "qemu/osdep.h"
#include "qapi/error.h"

#include "crypto/ivgenpriv.h"
#include "crypto/ivgen-plain.h"
#include "crypto/ivgen-plain64.h"
#include "crypto/ivgen-essiv.h"


QCryptoIVGen *qcrypto_ivgen_new(QCryptoIVGenAlgorithm alg,
                                QCryptoCipherAlgorithm cipheralg,
                                QCryptoHashAlgorithm hash,
                                const uint8_t *key, size_t nkey,
                                Error **errp)
{
    QCryptoIVGen *ivgen = g_new0(QCryptoIVGen, 1);

    ivgen->algorithm = alg;
    ivgen->cipher = cipheralg;
    ivgen->hash = hash;

    switch (alg) {
    case QCRYPTO_IVGEN_ALG_PLAIN:
        ivgen->driver = &qcrypto_ivgen_plain;
        break;
    case QCRYPTO_IVGEN_ALG_PLAIN64:
        ivgen->driver = &qcrypto_ivgen_plain64;
        break;
    case QCRYPTO_IVGEN_ALG_ESSIV:
        ivgen->driver = &qcrypto_ivgen_essiv;
        break;
    default:
        error_setg(errp, "Unknown block IV generator algorithm %d", alg);
        g_free(ivgen);
        return NULL;
    }

    if (ivgen->driver->init(ivgen, key, nkey, errp) < 0) {
        g_free(ivgen);
        return NULL;
    }

    return ivgen;
}


int qcrypto_ivgen_calculate(QCryptoIVGen *ivgen,
                            uint64_t sector,
                            uint8_t *iv, size_t niv,
                            Error **errp)
{
    return ivgen->driver->calculate(ivgen, sector, iv, niv, errp);
}


QCryptoIVGenAlgorithm qcrypto_ivgen_get_algorithm(QCryptoIVGen *ivgen)
{
    return ivgen->algorithm;
}


QCryptoCipherAlgorithm qcrypto_ivgen_get_cipher(QCryptoIVGen *ivgen)
{
    return ivgen->cipher;
}


QCryptoHashAlgorithm qcrypto_ivgen_get_hash(QCryptoIVGen *ivgen)
{
    return ivgen->hash;
}


void qcrypto_ivgen_free(QCryptoIVGen *ivgen)
{
    if (!ivgen) {
        return;
    }
    ivgen->driver->cleanup(ivgen);
    g_free(ivgen);
}
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