fe-secure-gssapi.c

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/*-------------------------------------------------------------------------
 *
 * fe-secure-gssapi.c
 *   The front-end (client) encryption support for GSSAPI
 *
 * Portions Copyright (c) 2016-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *  src/interfaces/libpq/fe-secure-gssapi.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include "fe-gssapi-common.h"
#include "libpq-fe.h"
#include "libpq-int.h"
#include "port/pg_bswap.h"


/*
 * Require encryption support, as well as mutual authentication and
 * tamperproofing measures.
 */
#define GSS_REQUIRED_FLAGS GSS_C_MUTUAL_FLAG | GSS_C_REPLAY_FLAG | \
    GSS_C_SEQUENCE_FLAG | GSS_C_CONF_FLAG | GSS_C_INTEG_FLAG

/*
 * Handle the encryption/decryption of data using GSSAPI.
 *
 * In the encrypted data stream on the wire, we break up the data
 * into packets where each packet starts with a uint32-size length
 * word (in network byte order), then encrypted data of that length
 * immediately following.  Decryption yields the same data stream
 * that would appear when not using encryption.
 *
 * Encrypted data typically ends up being larger than the same data
 * unencrypted, so we use fixed-size buffers for handling the
 * encryption/decryption which are larger than PQComm's buffer will
 * typically be to minimize the times where we have to make multiple
 * packets (and therefore multiple recv/send calls for a single
 * read/write call to us).
 *
 * NOTE: The client and server have to agree on the max packet size,
 * because we have to pass an entire packet to GSSAPI at a time and we
 * don't want the other side to send arbitrarily huge packets as we
 * would have to allocate memory for them to then pass them to GSSAPI.
 *
 * Therefore, these two #define's are effectively part of the protocol
 * spec and can't ever be changed.
 */
#define PQ_GSS_SEND_BUFFER_SIZE 16384
#define PQ_GSS_RECV_BUFFER_SIZE 16384

/*
 * We need these state variables per-connection.  To allow the functions
 * in this file to look mostly like those in be-secure-gssapi.c, set up
 * these macros.
 */
#define PqGSSSendBuffer (conn->gss_SendBuffer)
#define PqGSSSendLength (conn->gss_SendLength)
#define PqGSSSendNext (conn->gss_SendNext)
#define PqGSSSendConsumed (conn->gss_SendConsumed)
#define PqGSSRecvBuffer (conn->gss_RecvBuffer)
#define PqGSSRecvLength (conn->gss_RecvLength)
#define PqGSSResultBuffer (conn->gss_ResultBuffer)
#define PqGSSResultLength (conn->gss_ResultLength)
#define PqGSSResultNext (conn->gss_ResultNext)
#define PqGSSMaxPktSize (conn->gss_MaxPktSize)


/*
 * Attempt to write len bytes of data from ptr to a GSSAPI-encrypted connection.
 *
 * The connection must be already set up for GSSAPI encryption (i.e., GSSAPI
 * transport negotiation is complete).
 *
 * On success, returns the number of data bytes consumed (possibly less than
 * len).  On failure, returns -1 with errno set appropriately.  If the errno
 * indicates a non-retryable error, a message is added to conn->errorMessage.
 * For retryable errors, caller should call again (passing the same data)
 * once the socket is ready.
 */
ssize_t
pg_GSS_write(PGconn *conn, const void *ptr, size_t len)
{
    OM_uint32   major,
                minor;
    gss_buffer_desc input,
                output = GSS_C_EMPTY_BUFFER;
    ssize_t     ret = -1;
    size_t      bytes_sent = 0;
    size_t      bytes_to_encrypt;
    size_t      bytes_encrypted;
    gss_ctx_id_t gctx = conn->gctx;

    /*
     * When we get a failure, we must not tell the caller we have successfully
     * transmitted everything, else it won't retry.  Hence a "success"
     * (positive) return value must only count source bytes corresponding to
     * fully-transmitted encrypted packets.  The amount of source data
     * corresponding to the current partly-transmitted packet is remembered in
     * PqGSSSendConsumed.  On a retry, the caller *must* be sending that data
     * again, so if it offers a len less than that, something is wrong.
     */
    if (len < PqGSSSendConsumed)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             "GSSAPI caller failed to retransmit all data needing to be retried\n");
        errno = EINVAL;
        return -1;
    }

    /* Discount whatever source data we already encrypted. */
    bytes_to_encrypt = len - PqGSSSendConsumed;
    bytes_encrypted = PqGSSSendConsumed;

    /*
     * Loop through encrypting data and sending it out until it's all done or
     * pqsecure_raw_write() complains (which would likely mean that the socket
     * is non-blocking and the requested send() would block, or there was some
     * kind of actual error).
     */
    while (bytes_to_encrypt || PqGSSSendLength)
    {
        int         conf_state = 0;
        uint32      netlen;

        /*
         * Check if we have data in the encrypted output buffer that needs to
         * be sent (possibly left over from a previous call), and if so, try
         * to send it.  If we aren't able to, return that fact back up to the
         * caller.
         */
        if (PqGSSSendLength)
        {
            ssize_t     ret;
            ssize_t     amount = PqGSSSendLength - PqGSSSendNext;

            ret = pqsecure_raw_write(conn, PqGSSSendBuffer + PqGSSSendNext, amount);
            if (ret <= 0)
            {
                /*
                 * Report any previously-sent data; if there was none, reflect
                 * the pqsecure_raw_write result up to our caller.  When there
                 * was some, we're effectively assuming that any interesting
                 * failure condition will recur on the next try.
                 */
                if (bytes_sent)
                    return bytes_sent;
                return ret;
            }

            /*
             * Check if this was a partial write, and if so, move forward that
             * far in our buffer and try again.
             */
            if (ret != amount)
            {
                PqGSSSendNext += ret;
                continue;
            }

            /* We've successfully sent whatever data was in that packet. */
            bytes_sent += PqGSSSendConsumed;

            /* All encrypted data was sent, our buffer is empty now. */
            PqGSSSendLength = PqGSSSendNext = PqGSSSendConsumed = 0;
        }

        /*
         * Check if there are any bytes left to encrypt.  If not, we're done.
         */
        if (!bytes_to_encrypt)
            break;

        /*
         * Check how much we are being asked to send, if it's too much, then
         * we will have to loop and possibly be called multiple times to get
         * through all the data.
         */
        if (bytes_to_encrypt > PqGSSMaxPktSize)
            input.length = PqGSSMaxPktSize;
        else
            input.length = bytes_to_encrypt;

        input.value = (char *) ptr + bytes_encrypted;

        output.value = NULL;
        output.length = 0;

        /*
         * Create the next encrypted packet.  Any failure here is considered a
         * hard failure, so we return -1 even if bytes_sent > 0.
         */
        major = gss_wrap(&minor, gctx, 1, GSS_C_QOP_DEFAULT,
                         &input, &conf_state, &output);
        if (major != GSS_S_COMPLETE)
        {
            pg_GSS_error(libpq_gettext("GSSAPI wrap error"), conn, major, minor);
            errno = EIO;        /* for lack of a better idea */
            goto cleanup;
        }

        if (conf_state == 0)
        {
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("outgoing GSSAPI message would not use confidentiality\n"));
            errno = EIO;        /* for lack of a better idea */
            goto cleanup;
        }

        if (output.length > PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32))
        {
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("client tried to send oversize GSSAPI packet (%zu > %zu)\n"),
                              (size_t) output.length,
                              PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32));
            errno = EIO;        /* for lack of a better idea */
            goto cleanup;
        }

        bytes_encrypted += input.length;
        bytes_to_encrypt -= input.length;
        PqGSSSendConsumed += input.length;

        /* 4 network-order bytes of length, then payload */
        netlen = pg_hton32(output.length);
        memcpy(PqGSSSendBuffer + PqGSSSendLength, &netlen, sizeof(uint32));
        PqGSSSendLength += sizeof(uint32);

        memcpy(PqGSSSendBuffer + PqGSSSendLength, output.value, output.length);
        PqGSSSendLength += output.length;

        /* Release buffer storage allocated by GSSAPI */
        gss_release_buffer(&minor, &output);
    }

    /* If we get here, our counters should all match up. */
    Assert(bytes_sent == len);
    Assert(bytes_sent == bytes_encrypted);

    ret = bytes_sent;

cleanup:
    /* Release GSSAPI buffer storage, if we didn't already */
    if (output.value != NULL)
        gss_release_buffer(&minor, &output);
    return ret;
}

/*
 * Read up to len bytes of data into ptr from a GSSAPI-encrypted connection.
 *
 * The connection must be already set up for GSSAPI encryption (i.e., GSSAPI
 * transport negotiation is complete).
 *
 * Returns the number of data bytes read, or on failure, returns -1
 * with errno set appropriately.  If the errno indicates a non-retryable
 * error, a message is added to conn->errorMessage.  For retryable errors,
 * caller should call again once the socket is ready.
 */
ssize_t
pg_GSS_read(PGconn *conn, void *ptr, size_t len)
{
    OM_uint32   major,
                minor;
    gss_buffer_desc input = GSS_C_EMPTY_BUFFER,
                output = GSS_C_EMPTY_BUFFER;
    ssize_t     ret;
    size_t      bytes_returned = 0;
    gss_ctx_id_t gctx = conn->gctx;

    /*
     * The plan here is to read one incoming encrypted packet into
     * PqGSSRecvBuffer, decrypt it into PqGSSResultBuffer, and then dole out
     * data from there to the caller.  When we exhaust the current input
     * packet, read another.
     */
    while (bytes_returned < len)
    {
        int         conf_state = 0;

        /* Check if we have data in our buffer that we can return immediately */
        if (PqGSSResultNext < PqGSSResultLength)
        {
            size_t      bytes_in_buffer = PqGSSResultLength - PqGSSResultNext;
            size_t      bytes_to_copy = Min(bytes_in_buffer, len - bytes_returned);

            /*
             * Copy the data from our result buffer into the caller's buffer,
             * at the point where we last left off filling their buffer.
             */
            memcpy((char *) ptr + bytes_returned, PqGSSResultBuffer + PqGSSResultNext, bytes_to_copy);
            PqGSSResultNext += bytes_to_copy;
            bytes_returned += bytes_to_copy;

            /*
             * At this point, we've either filled the caller's buffer or
             * emptied our result buffer.  Either way, return to caller.  In
             * the second case, we could try to read another encrypted packet,
             * but the odds are good that there isn't one available.  (If this
             * isn't true, we chose too small a max packet size.)  In any
             * case, there's no harm letting the caller process the data we've
             * already returned.
             */
            break;
        }

        /* Result buffer is empty, so reset buffer pointers */
        PqGSSResultLength = PqGSSResultNext = 0;

        /*
         * Because we chose above to return immediately as soon as we emit
         * some data, bytes_returned must be zero at this point.  Therefore
         * the failure exits below can just return -1 without worrying about
         * whether we already emitted some data.
         */
        Assert(bytes_returned == 0);

        /*
         * At this point, our result buffer is empty with more bytes being
         * requested to be read.  We are now ready to load the next packet and
         * decrypt it (entirely) into our result buffer.
         */

        /* Collect the length if we haven't already */
        if (PqGSSRecvLength < sizeof(uint32))
        {
            ret = pqsecure_raw_read(conn, PqGSSRecvBuffer + PqGSSRecvLength,
                                    sizeof(uint32) - PqGSSRecvLength);

            /* If ret <= 0, pqsecure_raw_read already set the correct errno */
            if (ret <= 0)
                return ret;

            PqGSSRecvLength += ret;

            /* If we still haven't got the length, return to the caller */
            if (PqGSSRecvLength < sizeof(uint32))
            {
                errno = EWOULDBLOCK;
                return -1;
            }
        }

        /* Decode the packet length and check for overlength packet */
        input.length = pg_ntoh32(*(uint32 *) PqGSSRecvBuffer);

        if (input.length > PQ_GSS_RECV_BUFFER_SIZE - sizeof(uint32))
        {
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("oversize GSSAPI packet sent by the server (%zu > %zu)\n"),
                              (size_t) input.length,
                              PQ_GSS_RECV_BUFFER_SIZE - sizeof(uint32));
            errno = EIO;        /* for lack of a better idea */
            return -1;
        }

        /*
         * Read as much of the packet as we are able to on this call into
         * wherever we left off from the last time we were called.
         */
        ret = pqsecure_raw_read(conn, PqGSSRecvBuffer + PqGSSRecvLength,
                                input.length - (PqGSSRecvLength - sizeof(uint32)));
        /* If ret <= 0, pqsecure_raw_read already set the correct errno */
        if (ret <= 0)
            return ret;

        PqGSSRecvLength += ret;

        /* If we don't yet have the whole packet, return to the caller */
        if (PqGSSRecvLength - sizeof(uint32) < input.length)
        {
            errno = EWOULDBLOCK;
            return -1;
        }

        /*
         * We now have the full packet and we can perform the decryption and
         * refill our result buffer, then loop back up to pass data back to
         * the caller.  Note that error exits below here must take care of
         * releasing the gss output buffer.
         */
        output.value = NULL;
        output.length = 0;
        input.value = PqGSSRecvBuffer + sizeof(uint32);

        major = gss_unwrap(&minor, gctx, &input, &output, &conf_state, NULL);
        if (major != GSS_S_COMPLETE)
        {
            pg_GSS_error(libpq_gettext("GSSAPI unwrap error"), conn,
                         major, minor);
            ret = -1;
            errno = EIO;        /* for lack of a better idea */
            goto cleanup;
        }

        if (conf_state == 0)
        {
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("incoming GSSAPI message did not use confidentiality\n"));
            ret = -1;
            errno = EIO;        /* for lack of a better idea */
            goto cleanup;
        }

        memcpy(PqGSSResultBuffer, output.value, output.length);
        PqGSSResultLength = output.length;

        /* Our receive buffer is now empty, reset it */
        PqGSSRecvLength = 0;

        /* Release buffer storage allocated by GSSAPI */
        gss_release_buffer(&minor, &output);
    }

    ret = bytes_returned;

cleanup:
    /* Release GSSAPI buffer storage, if we didn't already */
    if (output.value != NULL)
        gss_release_buffer(&minor, &output);
    return ret;
}

/*
 * Simple wrapper for reading from pqsecure_raw_read.
 *
 * This takes the same arguments as pqsecure_raw_read, plus an output parameter
 * to return the number of bytes read.  This handles if blocking would occur and
 * if we detect EOF on the connection.
 */
static PostgresPollingStatusType
gss_read(PGconn *conn, void *recv_buffer, size_t length, ssize_t *ret)
{
    *ret = pqsecure_raw_read(conn, recv_buffer, length);
    if (*ret < 0)
    {
        if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
            return PGRES_POLLING_READING;
        else
            return PGRES_POLLING_FAILED;
    }

    /* Check for EOF */
    if (*ret == 0)
    {
        int         result = pqReadReady(conn);

        if (result < 0)
            return PGRES_POLLING_FAILED;

        if (!result)
            return PGRES_POLLING_READING;

        *ret = pqsecure_raw_read(conn, recv_buffer, length);
        if (*ret < 0)
        {
            if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
                return PGRES_POLLING_READING;
            else
                return PGRES_POLLING_FAILED;
        }
        if (*ret == 0)
            return PGRES_POLLING_FAILED;
    }

    return PGRES_POLLING_OK;
}

/*
 * Negotiate GSSAPI transport for a connection.  When complete, returns
 * PGRES_POLLING_OK.  Will return PGRES_POLLING_READING or
 * PGRES_POLLING_WRITING as appropriate whenever it would block, and
 * PGRES_POLLING_FAILED if transport could not be negotiated.
 */
PostgresPollingStatusType
pqsecure_open_gss(PGconn *conn)
{
    ssize_t     ret;
    OM_uint32   major,
                minor;
    uint32      netlen;
    PostgresPollingStatusType result;
    gss_buffer_desc input = GSS_C_EMPTY_BUFFER,
                output = GSS_C_EMPTY_BUFFER;

    /*
     * If first time through for this connection, allocate buffers and
     * initialize state variables.  By malloc'ing the buffers separately, we
     * ensure that they are sufficiently aligned for the length-word accesses
     * that we do in some places in this file.
     */
    if (PqGSSSendBuffer == NULL)
    {
        PqGSSSendBuffer = malloc(PQ_GSS_SEND_BUFFER_SIZE);
        PqGSSRecvBuffer = malloc(PQ_GSS_RECV_BUFFER_SIZE);
        PqGSSResultBuffer = malloc(PQ_GSS_RECV_BUFFER_SIZE);
        if (!PqGSSSendBuffer || !PqGSSRecvBuffer || !PqGSSResultBuffer)
        {
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("out of memory\n"));
            return PGRES_POLLING_FAILED;
        }
        PqGSSSendLength = PqGSSSendNext = PqGSSSendConsumed = 0;
        PqGSSRecvLength = PqGSSResultLength = PqGSSResultNext = 0;
    }

    /*
     * Check if we have anything to send from a prior call and if so, send it.
     */
    if (PqGSSSendLength)
    {
        ssize_t     amount = PqGSSSendLength - PqGSSSendNext;

        ret = pqsecure_raw_write(conn, PqGSSSendBuffer + PqGSSSendNext, amount);
        if (ret < 0)
        {
            if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
                return PGRES_POLLING_WRITING;
            else
                return PGRES_POLLING_FAILED;
        }

        if (ret < amount)
        {
            PqGSSSendNext += ret;
            return PGRES_POLLING_WRITING;
        }

        PqGSSSendLength = PqGSSSendNext = 0;
    }

    /*
     * Client sends first, and sending creates a context, therefore this will
     * be false the first time through, and then when we get called again we
     * will check for incoming data.
     */
    if (conn->gctx)
    {
        /* Process any incoming data we might have */

        /* See if we are still trying to get the length */
        if (PqGSSRecvLength < sizeof(uint32))
        {
            /* Attempt to get the length first */
            result = gss_read(conn, PqGSSRecvBuffer + PqGSSRecvLength, sizeof(uint32) - PqGSSRecvLength, &ret);
            if (result != PGRES_POLLING_OK)
                return result;

            PqGSSRecvLength += ret;

            if (PqGSSRecvLength < sizeof(uint32))
                return PGRES_POLLING_READING;
        }

        /*
         * Check if we got an error packet
         *
         * This is safe to do because we shouldn't ever get a packet over 8192
         * and therefore the actual length bytes, being that they are in
         * network byte order, for any real packet will start with two zero
         * bytes.
         */
        if (PqGSSRecvBuffer[0] == 'E')
        {
            /*
             * For an error packet during startup, we don't get a length, so
             * simply read as much as we can fit into our buffer (as a string,
             * so leave a spot at the end for a NULL byte too) and report that
             * back to the caller.
             */
            result = gss_read(conn, PqGSSRecvBuffer + PqGSSRecvLength, PQ_GSS_RECV_BUFFER_SIZE - PqGSSRecvLength - 1, &ret);
            if (result != PGRES_POLLING_OK)
                return result;

            PqGSSRecvLength += ret;

            appendPQExpBuffer(&conn->errorMessage, "%s\n", PqGSSRecvBuffer + 1);

            return PGRES_POLLING_FAILED;
        }

        /*
         * We should have the whole length at this point, so pull it out and
         * then read whatever we have left of the packet
         */

        /* Get the length and check for over-length packet */
        input.length = pg_ntoh32(*(uint32 *) PqGSSRecvBuffer);
        if (input.length > PQ_GSS_RECV_BUFFER_SIZE - sizeof(uint32))
        {
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("oversize GSSAPI packet sent by the server (%zu > %zu)\n"),
                              (size_t) input.length,
                              PQ_GSS_RECV_BUFFER_SIZE - sizeof(uint32));
            return PGRES_POLLING_FAILED;
        }

        /*
         * Read as much of the packet as we are able to on this call into
         * wherever we left off from the last time we were called.
         */
        result = gss_read(conn, PqGSSRecvBuffer + PqGSSRecvLength,
                          input.length - (PqGSSRecvLength - sizeof(uint32)), &ret);
        if (result != PGRES_POLLING_OK)
            return result;

        PqGSSRecvLength += ret;

        /*
         * If we got less than the rest of the packet then we need to return
         * and be called again.
         */
        if (PqGSSRecvLength - sizeof(uint32) < input.length)
            return PGRES_POLLING_READING;

        input.value = PqGSSRecvBuffer + sizeof(uint32);
    }

    /* Load the service name (no-op if already done */
    ret = pg_GSS_load_servicename(conn);
    if (ret != STATUS_OK)
        return PGRES_POLLING_FAILED;

    /*
     * Call GSS init context, either with an empty input, or with a complete
     * packet from the server.
     */
    major = gss_init_sec_context(&minor, conn->gcred, &conn->gctx,
                                 conn->gtarg_nam, GSS_C_NO_OID,
                                 GSS_REQUIRED_FLAGS, 0, 0, &input, NULL,
                                 &output, NULL, NULL);

    /* GSS Init Sec Context uses the whole packet, so clear it */
    PqGSSRecvLength = 0;

    if (GSS_ERROR(major))
    {
        pg_GSS_error(libpq_gettext("could not initiate GSSAPI security context"),
                     conn, major, minor);
        return PGRES_POLLING_FAILED;
    }

    if (output.length == 0)
    {
        /*
         * We're done - hooray!  Set flag to tell the low-level I/O routines
         * to do GSS wrapping/unwrapping.
         */
        conn->gssenc = true;

        /* Clean up */
        gss_release_cred(&minor, &conn->gcred);
        conn->gcred = GSS_C_NO_CREDENTIAL;
        gss_release_buffer(&minor, &output);

        /*
         * Determine the max packet size which will fit in our buffer, after
         * accounting for the length.  pg_GSS_write will need this.
         */
        major = gss_wrap_size_limit(&minor, conn->gctx, 1, GSS_C_QOP_DEFAULT,
                                    PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32),
                                    &PqGSSMaxPktSize);

        if (GSS_ERROR(major))
        {
            pg_GSS_error(libpq_gettext("GSSAPI size check error"), conn,
                         major, minor);
            return PGRES_POLLING_FAILED;
        }

        return PGRES_POLLING_OK;
    }

    /* Must have output.length > 0 */
    if (output.length > PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32))
    {
        pg_GSS_error(libpq_gettext("GSSAPI context establishment error"),
                     conn, major, minor);
        gss_release_buffer(&minor, &output);
        return PGRES_POLLING_FAILED;
    }

    /* Queue the token for writing */
    netlen = pg_hton32(output.length);

    memcpy(PqGSSSendBuffer, (char *) &netlen, sizeof(uint32));
    PqGSSSendLength += sizeof(uint32);

    memcpy(PqGSSSendBuffer + PqGSSSendLength, output.value, output.length);
    PqGSSSendLength += output.length;

    /* We don't bother with PqGSSSendConsumed here */

    /* Release buffer storage allocated by GSSAPI */
    gss_release_buffer(&minor, &output);

    /* Ask to be called again to write data */
    return PGRES_POLLING_WRITING;
}

/*
 * GSSAPI Information functions.
 */

/*
 * Return the GSSAPI Context itself.
 */
void *
PQgetgssctx(PGconn *conn)
{
    if (!conn)
        return NULL;

    return conn->gctx;
}

/*
 * Return true if GSSAPI encryption is in use.
 */
int
PQgssEncInUse(PGconn *conn)
{
    if (!conn || !conn->gctx)
        return 0;

    return conn->gssenc;
}