be-secure-gssapi.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * be-secure-gssapi.c
 *  GSSAPI encryption support
 *
 * Portions Copyright (c) 2018-2023, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *  src/backend/libpq/be-secure-gssapi.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <unistd.h>
 
#include "libpq/auth.h"
#include "libpq/be-gssapi-common.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "utils/memutils.h"
 
 
/*
 * 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
 
/*
 * Since we manage at most one GSS-encrypted connection per backend,
 * we can just keep all this state in static variables.  The char *
 * variables point to buffers that are allocated once and re-used.
 */
static char *PqGSSSendBuffer;   /* Encrypted data waiting to be sent */
static int  PqGSSSendLength;    /* End of data available in PqGSSSendBuffer */
static int  PqGSSSendNext;      /* Next index to send a byte from
                                 * PqGSSSendBuffer */
static int  PqGSSSendConsumed;  /* Number of *unencrypted* bytes consumed for
                                 * current contents of PqGSSSendBuffer */
 
static char *PqGSSRecvBuffer;   /* Received, encrypted data */
static int  PqGSSRecvLength;    /* End of data available in PqGSSRecvBuffer */
 
static char *PqGSSResultBuffer; /* Decryption of data in gss_RecvBuffer */
static int  PqGSSResultLength;  /* End of data available in PqGSSResultBuffer */
static int  PqGSSResultNext;    /* Next index to read a byte from
                                 * PqGSSResultBuffer */
 
static uint32 PqGSSMaxPktSize;  /* Maximum size we can encrypt and fit the
                                 * results into our output buffer */
 
 
/*
 * 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.  For retryable
 * errors, caller should call again (passing the same data) once the socket
 * is ready.
 *
 * Dealing with fatal errors here is a bit tricky: we can't invoke elog(FATAL)
 * since it would try to write to the client, probably resulting in infinite
 * recursion.  Instead, use elog(COMMERROR) to log extra info about the
 * failure if necessary, and then return an errno indicating connection loss.
 */
ssize_t
be_gssapi_write(Port *port, void *ptr, size_t len)
{
    OM_uint32   major,
                minor;
    gss_buffer_desc input,
                output;
    size_t      bytes_sent = 0;
    size_t      bytes_to_encrypt;
    size_t      bytes_encrypted;
    gss_ctx_id_t gctx = port->gss->ctx;
 
    /*
     * 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)
    {
        elog(COMMERROR, "GSSAPI caller failed to retransmit all data needing to be retried");
        errno = ECONNRESET;
        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
     * secure_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 = secure_raw_write(port, PqGSSSendBuffer + PqGSSSendNext, amount);
            if (ret <= 0)
            {
                /*
                 * Report any previously-sent data; if there was none, reflect
                 * the secure_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 */
        major = gss_wrap(&minor, gctx, 1, GSS_C_QOP_DEFAULT,
                         &input, &conf_state, &output);
        if (major != GSS_S_COMPLETE)
        {
            pg_GSS_error(_("GSSAPI wrap error"), major, minor);
            errno = ECONNRESET;
            return -1;
        }
        if (conf_state == 0)
        {
            ereport(COMMERROR,
                    (errmsg("outgoing GSSAPI message would not use confidentiality")));
            errno = ECONNRESET;
            return -1;
        }
        if (output.length > PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32))
        {
            ereport(COMMERROR,
                    (errmsg("server tried to send oversize GSSAPI packet (%zu > %zu)",
                            (size_t) output.length,
                            PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32))));
            errno = ECONNRESET;
            return -1;
        }
 
        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);
 
    return bytes_sent;
}
 
/*
 * 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.  For retryable errors, caller should call
 * again once the socket is ready.
 *
 * We treat fatal errors the same as in be_gssapi_write(), even though the
 * argument about infinite recursion doesn't apply here.
 */
ssize_t
be_gssapi_read(Port *port, void *ptr, size_t len)
{
    OM_uint32   major,
                minor;
    gss_buffer_desc input,
                output;
    ssize_t     ret;
    size_t      bytes_returned = 0;
    gss_ctx_id_t gctx = port->gss->ctx;
 
    /*
     * 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 = secure_raw_read(port, PqGSSRecvBuffer + PqGSSRecvLength,
                                  sizeof(uint32) - PqGSSRecvLength);
 
            /* If ret <= 0, secure_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))
        {
            ereport(COMMERROR,
                    (errmsg("oversize GSSAPI packet sent by the client (%zu > %zu)",
                            (size_t) input.length,
                            PQ_GSS_RECV_BUFFER_SIZE - sizeof(uint32))));
            errno = ECONNRESET;
            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 = secure_raw_read(port, PqGSSRecvBuffer + PqGSSRecvLength,
                              input.length - (PqGSSRecvLength - sizeof(uint32)));
        /* If ret <= 0, secure_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.
         */
        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(_("GSSAPI unwrap error"), major, minor);
            errno = ECONNRESET;
            return -1;
        }
        if (conf_state == 0)
        {
            ereport(COMMERROR,
                    (errmsg("incoming GSSAPI message did not use confidentiality")));
            errno = ECONNRESET;
            return -1;
        }
 
        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);
    }
 
    return bytes_returned;
}
 
/*
 * Read the specified number of bytes off the wire, waiting using
 * WaitLatchOrSocket if we would block.
 *
 * Results are read into PqGSSRecvBuffer.
 *
 * Will always return either -1, to indicate a permanent error, or len.
 */
static ssize_t
read_or_wait(Port *port, ssize_t len)
{
    ssize_t     ret;
 
    /*
     * Keep going until we either read in everything we were asked to, or we
     * error out.
     */
    while (PqGSSRecvLength < len)
    {
        ret = secure_raw_read(port, PqGSSRecvBuffer + PqGSSRecvLength, len - PqGSSRecvLength);
 
        /*
         * If we got back an error and it wasn't just
         * EWOULDBLOCK/EAGAIN/EINTR, then give up.
         */
        if (ret < 0 &&
            !(errno == EWOULDBLOCK || errno == EAGAIN || errno == EINTR))
            return -1;
 
        /*
         * Ok, we got back either a positive value, zero, or a negative result
         * indicating we should retry.
         *
         * If it was zero or negative, then we wait on the socket to be
         * readable again.
         */
        if (ret <= 0)
        {
            WaitLatchOrSocket(MyLatch,
                              WL_SOCKET_READABLE | WL_EXIT_ON_PM_DEATH,
                              port->sock, 0, WAIT_EVENT_GSS_OPEN_SERVER);
 
            /*
             * If we got back zero bytes, and then waited on the socket to be
             * readable and got back zero bytes on a second read, then this is
             * EOF and the client hung up on us.
             *
             * If we did get data here, then we can just fall through and
             * handle it just as if we got data the first time.
             *
             * Otherwise loop back to the top and try again.
             */
            if (ret == 0)
            {
                ret = secure_raw_read(port, PqGSSRecvBuffer + PqGSSRecvLength, len - PqGSSRecvLength);
                if (ret == 0)
                    return -1;
            }
            if (ret < 0)
                continue;
        }
 
        PqGSSRecvLength += ret;
    }
 
    return len;
}
 
/*
 * Start up a GSSAPI-encrypted connection.  This performs GSSAPI
 * authentication; after this function completes, it is safe to call
 * be_gssapi_read and be_gssapi_write.  Returns -1 and logs on failure;
 * otherwise, returns 0 and marks the connection as ready for GSSAPI
 * encryption.
 *
 * Note that unlike the be_gssapi_read/be_gssapi_write functions, this
 * function WILL block on the socket to be ready for read/write (using
 * WaitLatchOrSocket) as appropriate while establishing the GSSAPI
 * session.
 */
ssize_t
secure_open_gssapi(Port *port)
{
    bool        complete_next = false;
    OM_uint32   major,
                minor;
    gss_cred_id_t delegated_creds;
 
    /*
     * Allocate subsidiary Port data for GSSAPI operations.
     */
    port->gss = (pg_gssinfo *)
        MemoryContextAllocZero(TopMemoryContext, sizeof(pg_gssinfo));
 
    delegated_creds = GSS_C_NO_CREDENTIAL;
    port->gss->delegated_creds = false;
 
    /*
     * Allocate buffers and initialize state variables.  By malloc'ing the
     * buffers at this point, we avoid wasting static data space in processes
     * that will never use them, and we ensure that the buffers are
     * sufficiently aligned for the length-word accesses that we do in some
     * places in this file.
     */
    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)
        ereport(FATAL,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
    PqGSSSendLength = PqGSSSendNext = PqGSSSendConsumed = 0;
    PqGSSRecvLength = PqGSSResultLength = PqGSSResultNext = 0;
 
    /*
     * Use the configured keytab, if there is one.  As we now require MIT
     * Kerberos, we might consider using the credential store extensions in
     * the future instead of the environment variable.
     */
    if (pg_krb_server_keyfile != NULL && pg_krb_server_keyfile[0] != '\0')
    {
        if (setenv("KRB5_KTNAME", pg_krb_server_keyfile, 1) != 0)
        {
            /* The only likely failure cause is OOM, so use that errcode */
            ereport(FATAL,
                    (errcode(ERRCODE_OUT_OF_MEMORY),
                     errmsg("could not set environment: %m")));
        }
    }
 
    while (true)
    {
        ssize_t     ret;
        gss_buffer_desc input,
                    output = GSS_C_EMPTY_BUFFER;
 
        /*
         * The client always sends first, so try to go ahead and read the
         * length and wait on the socket to be readable again if that fails.
         */
        ret = read_or_wait(port, sizeof(uint32));
        if (ret < 0)
            return ret;
 
        /*
         * Get the length for this packet from the length header.
         */
        input.length = pg_ntoh32(*(uint32 *) PqGSSRecvBuffer);
 
        /* Done with the length, reset our buffer */
        PqGSSRecvLength = 0;
 
        /*
         * During initialization, packets are always fully consumed and
         * shouldn't ever be over PQ_GSS_RECV_BUFFER_SIZE in length.
         *
         * Verify on our side that the client doesn't do something funny.
         */
        if (input.length > PQ_GSS_RECV_BUFFER_SIZE)
        {
            ereport(COMMERROR,
                    (errmsg("oversize GSSAPI packet sent by the client (%zu > %d)",
                            (size_t) input.length,
                            PQ_GSS_RECV_BUFFER_SIZE)));
            return -1;
        }
 
        /*
         * Get the rest of the packet so we can pass it to GSSAPI to accept
         * the context.
         */
        ret = read_or_wait(port, input.length);
        if (ret < 0)
            return ret;
 
        input.value = PqGSSRecvBuffer;
 
        /* Process incoming data.  (The client sends first.) */
        major = gss_accept_sec_context(&minor, &port->gss->ctx,
                                       GSS_C_NO_CREDENTIAL, &input,
                                       GSS_C_NO_CHANNEL_BINDINGS,
                                       &port->gss->name, NULL, &output, NULL,
                                       NULL, pg_gss_accept_delegation ? &delegated_creds : NULL);
 
        if (GSS_ERROR(major))
        {
            pg_GSS_error(_("could not accept GSSAPI security context"),
                         major, minor);
            gss_release_buffer(&minor, &output);
            return -1;
        }
        else if (!(major & GSS_S_CONTINUE_NEEDED))
        {
            /*
             * rfc2744 technically permits context negotiation to be complete
             * both with and without a packet to be sent.
             */
            complete_next = true;
        }
 
        if (delegated_creds != GSS_C_NO_CREDENTIAL)
        {
            pg_store_delegated_credential(delegated_creds);
            port->gss->delegated_creds = true;
        }
 
        /* Done handling the incoming packet, reset our buffer */
        PqGSSRecvLength = 0;
 
        /*
         * Check if we have data to send and, if we do, make sure to send it
         * all
         */
        if (output.length > 0)
        {
            uint32      netlen = pg_hton32(output.length);
 
            if (output.length > PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32))
            {
                ereport(COMMERROR,
                        (errmsg("server tried to send oversize GSSAPI packet (%zu > %zu)",
                                (size_t) output.length,
                                PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32))));
                gss_release_buffer(&minor, &output);
                return -1;
            }
 
            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 */
 
            while (PqGSSSendNext < PqGSSSendLength)
            {
                ret = secure_raw_write(port, PqGSSSendBuffer + PqGSSSendNext,
                                       PqGSSSendLength - PqGSSSendNext);
 
                /*
                 * If we got back an error and it wasn't just
                 * EWOULDBLOCK/EAGAIN/EINTR, then give up.
                 */
                if (ret < 0 &&
                    !(errno == EWOULDBLOCK || errno == EAGAIN || errno == EINTR))
                {
                    gss_release_buffer(&minor, &output);
                    return -1;
                }
 
                /* Wait and retry if we couldn't write yet */
                if (ret <= 0)
                {
                    WaitLatchOrSocket(MyLatch,
                                      WL_SOCKET_WRITEABLE | WL_EXIT_ON_PM_DEATH,
                                      port->sock, 0, WAIT_EVENT_GSS_OPEN_SERVER);
                    continue;
                }
 
                PqGSSSendNext += ret;
            }
 
            /* Done sending the packet, reset our buffer */
            PqGSSSendLength = PqGSSSendNext = 0;
 
            gss_release_buffer(&minor, &output);
        }
 
        /*
         * If we got back that the connection is finished being set up, now
         * that we've sent the last packet, exit our loop.
         */
        if (complete_next)
            break;
    }
 
    /*
     * Determine the max packet size which will fit in our buffer, after
     * accounting for the length.  be_gssapi_write will need this.
     */
    major = gss_wrap_size_limit(&minor, port->gss->ctx, 1, GSS_C_QOP_DEFAULT,
                                PQ_GSS_SEND_BUFFER_SIZE - sizeof(uint32),
                                &PqGSSMaxPktSize);
 
    if (GSS_ERROR(major))
    {
        pg_GSS_error(_("GSSAPI size check error"), major, minor);
        return -1;
    }
 
    port->gss->enc = true;
 
    return 0;
}
 
/*
 * Return if GSSAPI authentication was used on this connection.
 */
bool
be_gssapi_get_auth(Port *port)
{
    if (!port || !port->gss)
        return false;
 
    return port->gss->auth;
}
 
/*
 * Return if GSSAPI encryption is enabled and being used on this connection.
 */
bool
be_gssapi_get_enc(Port *port)
{
    if (!port || !port->gss)
        return false;
 
    return port->gss->enc;
}
 
/*
 * Return the GSSAPI principal used for authentication on this connection
 * (NULL if we did not perform GSSAPI authentication).
 */
const char *
be_gssapi_get_princ(Port *port)
{
    if (!port || !port->gss)
        return NULL;
 
    return port->gss->princ;
}
 
/*
 * Return if GSSAPI delegated credentials were included on this
 * connection.
 */
bool
be_gssapi_get_delegation(Port *port)
{
    if (!port || !port->gss)
        return false;
 
    return port->gss->delegated_creds;
}