Archipelago » qemu

/*

 * QEMU VNC display driver: SASL auth protocol

 *

 * Copyright (C) 2009 Red Hat, Inc

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL

 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 */

#include "vnc.h"

/* Max amount of data we send/recv for SASL steps to prevent DOS */

#define SASL_DATA_MAX_LEN (1024 * 1024)

void vnc_sasl_client_cleanup(VncState *vs)

{

    if (vs->sasl.conn) {

        vs->sasl.runSSF = false;

        vs->sasl.wantSSF = false;

        vs->sasl.waitWriteSSF = 0;

        vs->sasl.encodedLength = vs->sasl.encodedOffset = 0;

        vs->sasl.encoded = NULL;

        g_free(vs->sasl.username);

        g_free(vs->sasl.mechlist);

        vs->sasl.username = vs->sasl.mechlist = NULL;

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

    }

}

long vnc_client_write_sasl(VncState *vs)

{

    long ret;

    VNC_DEBUG("Write SASL: Pending output %p size %zd offset %zd "

              "Encoded: %p size %d offset %d\n",

              vs->output.buffer, vs->output.capacity, vs->output.offset,

              vs->sasl.encoded, vs->sasl.encodedLength, vs->sasl.encodedOffset);

    if (!vs->sasl.encoded) {

        int err;

        err = sasl_encode(vs->sasl.conn,

                          (char *)vs->output.buffer,

                          vs->output.offset,

                          (const char **)&vs->sasl.encoded,

                          &vs->sasl.encodedLength);

        if (err != SASL_OK)

            return vnc_client_io_error(vs, -1, EIO);

        vs->sasl.encodedOffset = 0;

    }

    ret = vnc_client_write_buf(vs,

                               vs->sasl.encoded + vs->sasl.encodedOffset,

                               vs->sasl.encodedLength - vs->sasl.encodedOffset);

    if (!ret)

        return 0;

    vs->sasl.encodedOffset += ret;

    if (vs->sasl.encodedOffset == vs->sasl.encodedLength) {

        vs->output.offset = 0;

        vs->sasl.encoded = NULL;

        vs->sasl.encodedOffset = vs->sasl.encodedLength = 0;

    }

    /* Can't merge this block with one above, because

     * someone might have written more unencrypted

     * data in vs->output while we were processing

     * SASL encoded output

     */

    if (vs->output.offset == 0) {

        qemu_set_fd_handler2(vs->csock, NULL, vnc_client_read, NULL, vs);

    }

    return ret;

}

long vnc_client_read_sasl(VncState *vs)

{

    long ret;

    uint8_t encoded[4096];

    const char *decoded;

    unsigned int decodedLen;

    int err;

    ret = vnc_client_read_buf(vs, encoded, sizeof(encoded));

    if (!ret)

        return 0;

    err = sasl_decode(vs->sasl.conn,

                      (char *)encoded, ret,

                      &decoded, &decodedLen);

    if (err != SASL_OK)

        return vnc_client_io_error(vs, -1, -EIO);

    VNC_DEBUG("Read SASL Encoded %p size %ld Decoded %p size %d\n",

              encoded, ret, decoded, decodedLen);

    buffer_reserve(&vs->input, decodedLen);

    buffer_append(&vs->input, decoded, decodedLen);

    return decodedLen;

}

static int vnc_auth_sasl_check_access(VncState *vs)

{

    const void *val;

    int err;

    int allow;

    err = sasl_getprop(vs->sasl.conn, SASL_USERNAME, &val);

    if (err != SASL_OK) {

        VNC_DEBUG("cannot query SASL username on connection %d (%s), denying access\n",

                  err, sasl_errstring(err, NULL, NULL));

        return -1;

    }

    if (val == NULL) {

        VNC_DEBUG("no client username was found, denying access\n");

        return -1;

    }

    VNC_DEBUG("SASL client username %s\n", (const char *)val);

    vs->sasl.username = g_strdup((const char*)val);

    if (vs->vd->sasl.acl == NULL) {

        VNC_DEBUG("no ACL activated, allowing access\n");

        return 0;

    }

    allow = qemu_acl_party_is_allowed(vs->vd->sasl.acl, vs->sasl.username);

    VNC_DEBUG("SASL client %s %s by ACL\n", vs->sasl.username,

              allow ? "allowed" : "denied");

    return allow ? 0 : -1;

}

static int vnc_auth_sasl_check_ssf(VncState *vs)

{

    const void *val;

    int err, ssf;

    if (!vs->sasl.wantSSF)

        return 1;

    err = sasl_getprop(vs->sasl.conn, SASL_SSF, &val);

    if (err != SASL_OK)

        return 0;

    ssf = *(const int *)val;

    VNC_DEBUG("negotiated an SSF of %d\n", ssf);

    if (ssf < 56)

        return 0; /* 56 is good for Kerberos */

    /* Only setup for read initially, because we're about to send an RPC

     * reply which must be in plain text. When the next incoming RPC

     * arrives, we'll switch on writes too

     *

     * cf qemudClientReadSASL  in qemud.c

     */

    vs->sasl.runSSF = 1;

    /* We have a SSF that's good enough */

    return 1;

}

/*

 * Step Msg

 *

 * Input from client:

 *

 * u32 clientin-length

 * u8-array clientin-string

 *

 * Output to client:

 *

 * u32 serverout-length

 * u8-array serverout-strin

 * u8 continue

 */

static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len);

static int protocol_client_auth_sasl_step(VncState *vs, uint8_t *data, size_t len)

{

    uint32_t datalen = len;

    const char *serverout;

    unsigned int serveroutlen;

    int err;

    char *clientdata = NULL;

    /* NB, distinction of NULL vs "" is *critical* in SASL */

    if (datalen) {

        clientdata = (char*)data;

        clientdata[datalen-1] = '\0'; /* Wire includes '\0', but make sure */

        datalen--; /* Don't count NULL byte when passing to _start() */

    }

    VNC_DEBUG("Step using SASL Data %p (%d bytes)\n",

              clientdata, datalen);

    err = sasl_server_step(vs->sasl.conn,

                           clientdata,

                           datalen,

                           &serverout,

                           &serveroutlen);

    if (err != SASL_OK &&

        err != SASL_CONTINUE) {

        VNC_DEBUG("sasl step failed %d (%s)\n",

                  err, sasl_errdetail(vs->sasl.conn));

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

        goto authabort;

    }

    if (serveroutlen > SASL_DATA_MAX_LEN) {

        VNC_DEBUG("sasl step reply data too long %d\n",

                  serveroutlen);

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

        goto authabort;

    }

    VNC_DEBUG("SASL return data %d bytes, nil; %d\n",

              serveroutlen, serverout ? 0 : 1);

    if (serveroutlen) {

        vnc_write_u32(vs, serveroutlen + 1);

        vnc_write(vs, serverout, serveroutlen + 1);

    } else {

        vnc_write_u32(vs, 0);

    }

    /* Whether auth is complete */

    vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);

    if (err == SASL_CONTINUE) {

        VNC_DEBUG("%s", "Authentication must continue\n");

        /* Wait for step length */

        vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);

    } else {

        if (!vnc_auth_sasl_check_ssf(vs)) {

            VNC_DEBUG("Authentication rejected for weak SSF %d\n", vs->csock);

            goto authreject;

        }

        /* Check username whitelist ACL */

        if (vnc_auth_sasl_check_access(vs) < 0) {

            VNC_DEBUG("Authentication rejected for ACL %d\n", vs->csock);

            goto authreject;

        }

        VNC_DEBUG("Authentication successful %d\n", vs->csock);

        vnc_write_u32(vs, 0); /* Accept auth */

        /*

         * Delay writing in SSF encoded mode until pending output

         * buffer is written

         */

        if (vs->sasl.runSSF)

            vs->sasl.waitWriteSSF = vs->output.offset;

        start_client_init(vs);

    }

    return 0;

 authreject:

    vnc_write_u32(vs, 1); /* Reject auth */

    vnc_write_u32(vs, sizeof("Authentication failed"));

    vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));

    vnc_flush(vs);

    vnc_client_error(vs);

    return -1;

 authabort:

    vnc_client_error(vs);

    return -1;

}

static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len)

{

    uint32_t steplen = read_u32(data, 0);

    VNC_DEBUG("Got client step len %d\n", steplen);

    if (steplen > SASL_DATA_MAX_LEN) {

        VNC_DEBUG("Too much SASL data %d\n", steplen);

        vnc_client_error(vs);

        return -1;

    }

    if (steplen == 0)

        return protocol_client_auth_sasl_step(vs, NULL, 0);

    else

        vnc_read_when(vs, protocol_client_auth_sasl_step, steplen);

    return 0;

}

/*

 * Start Msg

 *

 * Input from client:

 *

 * u32 clientin-length

 * u8-array clientin-string

 *

 * Output to client:

 *

 * u32 serverout-length

 * u8-array serverout-strin

 * u8 continue

 */

#define SASL_DATA_MAX_LEN (1024 * 1024)

static int protocol_client_auth_sasl_start(VncState *vs, uint8_t *data, size_t len)

{

    uint32_t datalen = len;

    const char *serverout;

    unsigned int serveroutlen;

    int err;

    char *clientdata = NULL;

    /* NB, distinction of NULL vs "" is *critical* in SASL */

    if (datalen) {

        clientdata = (char*)data;

        clientdata[datalen-1] = '\0'; /* Should be on wire, but make sure */

        datalen--; /* Don't count NULL byte when passing to _start() */

    }

    VNC_DEBUG("Start SASL auth with mechanism %s. Data %p (%d bytes)\n",

              vs->sasl.mechlist, clientdata, datalen);

    err = sasl_server_start(vs->sasl.conn,

                            vs->sasl.mechlist,

                            clientdata,

                            datalen,

                            &serverout,

                            &serveroutlen);

    if (err != SASL_OK &&

        err != SASL_CONTINUE) {

        VNC_DEBUG("sasl start failed %d (%s)\n",

                  err, sasl_errdetail(vs->sasl.conn));

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

        goto authabort;

    }

    if (serveroutlen > SASL_DATA_MAX_LEN) {

        VNC_DEBUG("sasl start reply data too long %d\n",

                  serveroutlen);

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

        goto authabort;

    }

    VNC_DEBUG("SASL return data %d bytes, nil; %d\n",

              serveroutlen, serverout ? 0 : 1);

    if (serveroutlen) {

        vnc_write_u32(vs, serveroutlen + 1);

        vnc_write(vs, serverout, serveroutlen + 1);

    } else {

        vnc_write_u32(vs, 0);

    }

    /* Whether auth is complete */

    vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);

    if (err == SASL_CONTINUE) {

        VNC_DEBUG("%s", "Authentication must continue\n");

        /* Wait for step length */

        vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);

    } else {

        if (!vnc_auth_sasl_check_ssf(vs)) {

            VNC_DEBUG("Authentication rejected for weak SSF %d\n", vs->csock);

            goto authreject;

        }

        /* Check username whitelist ACL */

        if (vnc_auth_sasl_check_access(vs) < 0) {

            VNC_DEBUG("Authentication rejected for ACL %d\n", vs->csock);

            goto authreject;

        }

        VNC_DEBUG("Authentication successful %d\n", vs->csock);

        vnc_write_u32(vs, 0); /* Accept auth */

        start_client_init(vs);

    }

    return 0;

 authreject:

    vnc_write_u32(vs, 1); /* Reject auth */

    vnc_write_u32(vs, sizeof("Authentication failed"));

    vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));

    vnc_flush(vs);

    vnc_client_error(vs);

    return -1;

 authabort:

    vnc_client_error(vs);

    return -1;

}

static int protocol_client_auth_sasl_start_len(VncState *vs, uint8_t *data, size_t len)

{

    uint32_t startlen = read_u32(data, 0);

    VNC_DEBUG("Got client start len %d\n", startlen);

    if (startlen > SASL_DATA_MAX_LEN) {

        VNC_DEBUG("Too much SASL data %d\n", startlen);

        vnc_client_error(vs);

        return -1;

    }

    if (startlen == 0)

        return protocol_client_auth_sasl_start(vs, NULL, 0);

    vnc_read_when(vs, protocol_client_auth_sasl_start, startlen);

    return 0;

}

static int protocol_client_auth_sasl_mechname(VncState *vs, uint8_t *data, size_t len)

{

    char *mechname = g_strndup((const char *) data, len);

    VNC_DEBUG("Got client mechname '%s' check against '%s'\n",

              mechname, vs->sasl.mechlist);

    if (strncmp(vs->sasl.mechlist, mechname, len) == 0) {

        if (vs->sasl.mechlist[len] != '\0' &&

            vs->sasl.mechlist[len] != ',') {

            VNC_DEBUG("One %d", vs->sasl.mechlist[len]);

            goto fail;

        }

    } else {

        char *offset = strstr(vs->sasl.mechlist, mechname);

        VNC_DEBUG("Two %p\n", offset);

        if (!offset) {

            goto fail;

        }

        VNC_DEBUG("Two '%s'\n", offset);

        if (offset[-1] != ',' ||

            (offset[len] != '\0'&&

             offset[len] != ',')) {

            goto fail;

        }

    }

    g_free(vs->sasl.mechlist);

    vs->sasl.mechlist = mechname;

    VNC_DEBUG("Validated mechname '%s'\n", mechname);

    vnc_read_when(vs, protocol_client_auth_sasl_start_len, 4);

    return 0;

 fail:

    vnc_client_error(vs);

    g_free(mechname);

    return -1;

}

static int protocol_client_auth_sasl_mechname_len(VncState *vs, uint8_t *data, size_t len)

{

    uint32_t mechlen = read_u32(data, 0);

    VNC_DEBUG("Got client mechname len %d\n", mechlen);

    if (mechlen > 100) {

        VNC_DEBUG("Too long SASL mechname data %d\n", mechlen);

        vnc_client_error(vs);

        return -1;

    }

    if (mechlen < 1) {

        VNC_DEBUG("Too short SASL mechname %d\n", mechlen);

        vnc_client_error(vs);

        return -1;

    }

    vnc_read_when(vs, protocol_client_auth_sasl_mechname,mechlen);

    return 0;

}

void start_auth_sasl(VncState *vs)

{

    const char *mechlist = NULL;

    sasl_security_properties_t secprops;

    int err;

    char *localAddr, *remoteAddr;

    int mechlistlen;

    VNC_DEBUG("Initialize SASL auth %d\n", vs->csock);

    /* Get local & remote client addresses in form  IPADDR;PORT */

    if (!(localAddr = vnc_socket_local_addr("%s;%s", vs->csock)))

        goto authabort;

    if (!(remoteAddr = vnc_socket_remote_addr("%s;%s", vs->csock))) {

        g_free(localAddr);

        goto authabort;

    }

    err = sasl_server_new("vnc",

                          NULL, /* FQDN - just delegates to gethostname */

                          NULL, /* User realm */

                          localAddr,

                          remoteAddr,

                          NULL, /* Callbacks, not needed */

                          SASL_SUCCESS_DATA,

                          &vs->sasl.conn);

    g_free(localAddr);

    g_free(remoteAddr);

    localAddr = remoteAddr = NULL;

    if (err != SASL_OK) {

        VNC_DEBUG("sasl context setup failed %d (%s)",

                  err, sasl_errstring(err, NULL, NULL));

        vs->sasl.conn = NULL;

        goto authabort;

    }

#ifdef CONFIG_VNC_TLS

    /* Inform SASL that we've got an external SSF layer from TLS/x509 */

    if (vs->auth == VNC_AUTH_VENCRYPT &&

        vs->subauth == VNC_AUTH_VENCRYPT_X509SASL) {

        gnutls_cipher_algorithm_t cipher;

        sasl_ssf_t ssf;

        cipher = gnutls_cipher_get(vs->tls.session);

        if (!(ssf = (sasl_ssf_t)gnutls_cipher_get_key_size(cipher))) {

            VNC_DEBUG("%s", "cannot TLS get cipher size\n");

            sasl_dispose(&vs->sasl.conn);

            vs->sasl.conn = NULL;

            goto authabort;

        }

        ssf *= 8; /* tls key size is bytes, sasl wants bits */

        err = sasl_setprop(vs->sasl.conn, SASL_SSF_EXTERNAL, &ssf);

        if (err != SASL_OK) {

            VNC_DEBUG("cannot set SASL external SSF %d (%s)\n",

                      err, sasl_errstring(err, NULL, NULL));

            sasl_dispose(&vs->sasl.conn);

            vs->sasl.conn = NULL;

            goto authabort;

        }

    } else

#endif /* CONFIG_VNC_TLS */

        vs->sasl.wantSSF = 1;

    memset (&secprops, 0, sizeof secprops);

    /* Inform SASL that we've got an external SSF layer from TLS */

    if (strncmp(vs->vd->display, "unix:", 5) == 0

#ifdef CONFIG_VNC_TLS

        /* Disable SSF, if using TLS+x509+SASL only. TLS without x509

           is not sufficiently strong */

        || (vs->auth == VNC_AUTH_VENCRYPT &&

            vs->subauth == VNC_AUTH_VENCRYPT_X509SASL)

#endif /* CONFIG_VNC_TLS */

        ) {

        /* If we've got TLS or UNIX domain sock, we don't care about SSF */

        secprops.min_ssf = 0;

        secprops.max_ssf = 0;

        secprops.maxbufsize = 8192;

        secprops.security_flags = 0;

    } else {

        /* Plain TCP, better get an SSF layer */

        secprops.min_ssf = 56; /* Good enough to require kerberos */

        secprops.max_ssf = 100000; /* Arbitrary big number */

        secprops.maxbufsize = 8192;

        /* Forbid any anonymous or trivially crackable auth */

        secprops.security_flags =

            SASL_SEC_NOANONYMOUS | SASL_SEC_NOPLAINTEXT;

    }

    err = sasl_setprop(vs->sasl.conn, SASL_SEC_PROPS, &secprops);

    if (err != SASL_OK) {

        VNC_DEBUG("cannot set SASL security props %d (%s)\n",

                  err, sasl_errstring(err, NULL, NULL));

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

        goto authabort;

    }

    err = sasl_listmech(vs->sasl.conn,

                        NULL, /* Don't need to set user */

                        "", /* Prefix */

                        ",", /* Separator */

                        "", /* Suffix */

                        &mechlist,

                        NULL,

                        NULL);

    if (err != SASL_OK) {

        VNC_DEBUG("cannot list SASL mechanisms %d (%s)\n",

                  err, sasl_errdetail(vs->sasl.conn));

        sasl_dispose(&vs->sasl.conn);

        vs->sasl.conn = NULL;

        goto authabort;

    }

    VNC_DEBUG("Available mechanisms for client: '%s'\n", mechlist);

    vs->sasl.mechlist = g_strdup(mechlist);

    mechlistlen = strlen(mechlist);

    vnc_write_u32(vs, mechlistlen);

    vnc_write(vs, mechlist, mechlistlen);

    vnc_flush(vs);

    VNC_DEBUG("Wait for client mechname length\n");

    vnc_read_when(vs, protocol_client_auth_sasl_mechname_len, 4);

    return;

 authabort:

    vnc_client_error(vs);

}