fe-secure.c

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/*-------------------------------------------------------------------------
 *
 * fe-secure.c
 *    functions related to setting up a secure connection to the backend.
 *    Secure connections are expected to provide confidentiality,
 *    message integrity and endpoint authentication.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-secure.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
 
#ifdef WIN32
#include "win32.h"
#else
#include <sys/socket.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#endif
 
#include <sys/stat.h>
 
#ifdef WIN32
#include "pthread-win32.h"
#else
#include <pthread.h>
#endif
 
#include "fe-auth.h"
#include "libpq-fe.h"
#include "libpq-int.h"
 
/*
 * Macros to handle disabling and then restoring the state of SIGPIPE handling.
 * On Windows, these are all no-ops since there's no SIGPIPEs.
 */
 
#ifndef WIN32
 
#define SIGPIPE_MASKED(conn)    ((conn)->sigpipe_so || (conn)->sigpipe_flag)
 
struct sigpipe_info
{
    sigset_t    oldsigmask;
    bool        sigpipe_pending;
    bool        got_epipe;
};
 
#define DECLARE_SIGPIPE_INFO(spinfo) struct sigpipe_info spinfo
 
#define DISABLE_SIGPIPE(conn, spinfo, failaction) \
    do { \
        (spinfo).got_epipe = false; \
        if (!SIGPIPE_MASKED(conn)) \
        { \
            if (pq_block_sigpipe(&(spinfo).oldsigmask, \
                                 &(spinfo).sigpipe_pending) < 0) \
                failaction; \
        } \
    } while (0)
 
#define REMEMBER_EPIPE(spinfo, cond) \
    do { \
        if (cond) \
            (spinfo).got_epipe = true; \
    } while (0)
 
#define RESTORE_SIGPIPE(conn, spinfo) \
    do { \
        if (!SIGPIPE_MASKED(conn)) \
            pq_reset_sigpipe(&(spinfo).oldsigmask, (spinfo).sigpipe_pending, \
                             (spinfo).got_epipe); \
    } while (0)
#else                           /* WIN32 */
 
#define DECLARE_SIGPIPE_INFO(spinfo)
#define DISABLE_SIGPIPE(conn, spinfo, failaction)
#define REMEMBER_EPIPE(spinfo, cond)
#define RESTORE_SIGPIPE(conn, spinfo)
#endif                          /* WIN32 */
 
/* ------------------------------------------------------------ */
/*           Procedures common to all secure sessions           */
/* ------------------------------------------------------------ */
 
 
int
PQsslInUse(PGconn *conn)
{
    if (!conn)
        return 0;
    return conn->ssl_in_use;
}
 
/*
 *  Exported function to allow application to tell us it's already
 *  initialized OpenSSL.
 */
void
PQinitSSL(int do_init)
{
#ifdef USE_SSL
    pgtls_init_library(do_init, do_init);
#endif
}
 
/*
 *  Exported function to allow application to tell us it's already
 *  initialized OpenSSL and/or libcrypto.
 */
void
PQinitOpenSSL(int do_ssl, int do_crypto)
{
#ifdef USE_SSL
    pgtls_init_library(do_ssl, do_crypto);
#endif
}
 
/*
 *  Initialize global SSL context
 */
int
pqsecure_initialize(PGconn *conn, bool do_ssl, bool do_crypto)
{
    int         r = 0;
 
#ifdef USE_SSL
    r = pgtls_init(conn, do_ssl, do_crypto);
#endif
 
    return r;
}
 
/*
 *  Begin or continue negotiating a secure session.
 */
PostgresPollingStatusType
pqsecure_open_client(PGconn *conn)
{
#ifdef USE_SSL
    return pgtls_open_client(conn);
#else
    /* shouldn't get here */
    return PGRES_POLLING_FAILED;
#endif
}
 
/*
 *  Close secure session.
 */
void
pqsecure_close(PGconn *conn)
{
#ifdef USE_SSL
    pgtls_close(conn);
#endif
}
 
/*
 *  Read data from a secure connection.
 *
 * On failure, this function is responsible for appending a suitable message
 * to conn->errorMessage.  The caller must still inspect errno, but only
 * to determine whether to continue/retry after error.
 */
ssize_t
pqsecure_read(PGconn *conn, void *ptr, size_t len)
{
    ssize_t     n;
 
#ifdef USE_SSL
    if (conn->ssl_in_use)
    {
        n = pgtls_read(conn, ptr, len);
    }
    else
#endif
#ifdef ENABLE_GSS
    if (conn->gssenc)
    {
        n = pg_GSS_read(conn, ptr, len);
    }
    else
#endif
    {
        n = pqsecure_raw_read(conn, ptr, len);
    }
 
    return n;
}
 
ssize_t
pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
{
    ssize_t     n;
    int         result_errno = 0;
    char        sebuf[PG_STRERROR_R_BUFLEN];
 
    n = recv(conn->sock, ptr, len, 0);
 
    if (n < 0)
    {
        result_errno = SOCK_ERRNO;
 
        /* Set error message if appropriate */
        switch (result_errno)
        {
#ifdef EAGAIN
            case EAGAIN:
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
            case EWOULDBLOCK:
#endif
            case EINTR:
                /* no error message, caller is expected to retry */
                break;
 
            case EPIPE:
            case ECONNRESET:
                libpq_append_conn_error(conn, "server closed the connection unexpectedly\n"
                                        "\tThis probably means the server terminated abnormally\n"
                                        "\tbefore or while processing the request.");
                break;
 
            default:
                libpq_append_conn_error(conn, "could not receive data from server: %s",
                                        SOCK_STRERROR(result_errno,
                                                      sebuf, sizeof(sebuf)));
                break;
        }
    }
 
    /* ensure we return the intended errno to caller */
    SOCK_ERRNO_SET(result_errno);
 
    return n;
}
 
/*
 *  Write data to a secure connection.
 *
 * Returns the number of bytes written, or a negative value (with errno
 * set) upon failure.  The write count could be less than requested.
 *
 * Note that socket-level hard failures are masked from the caller,
 * instead setting conn->write_failed and storing an error message
 * in conn->write_err_msg; see pqsecure_raw_write.  This allows us to
 * postpone reporting of write failures until we're sure no error
 * message is available from the server.
 *
 * However, errors detected in the SSL or GSS management level are reported
 * via a negative result, with message appended to conn->errorMessage.
 * It's frequently unclear whether such errors should be considered read or
 * write errors, so we don't attempt to postpone reporting them.
 *
 * The caller must still inspect errno upon failure, but only to determine
 * whether to continue/retry; a message has been saved someplace in any case.
 */
ssize_t
pqsecure_write(PGconn *conn, const void *ptr, size_t len)
{
    ssize_t     n;
 
#ifdef USE_SSL
    if (conn->ssl_in_use)
    {
        n = pgtls_write(conn, ptr, len);
    }
    else
#endif
#ifdef ENABLE_GSS
    if (conn->gssenc)
    {
        n = pg_GSS_write(conn, ptr, len);
    }
    else
#endif
    {
        n = pqsecure_raw_write(conn, ptr, len);
    }
 
    return n;
}
 
/*
 * Low-level implementation of pqsecure_write.
 *
 * This is used directly for an unencrypted connection.  For encrypted
 * connections, this does the physical I/O on behalf of pgtls_write or
 * pg_GSS_write.
 *
 * This function reports failure (i.e., returns a negative result) only
 * for retryable errors such as EINTR.  Looping for such cases is to be
 * handled at some outer level, maybe all the way up to the application.
 * For hard failures, we set conn->write_failed and store an error message
 * in conn->write_err_msg, but then claim to have written the data anyway.
 * This is because we don't want to report write failures so long as there
 * is a possibility of reading from the server and getting an error message
 * that could explain why the connection dropped.  Many TCP stacks have
 * race conditions such that a write failure may or may not be reported
 * before all incoming data has been read.
 *
 * Note that this error behavior happens below the SSL management level when
 * we are using SSL.  That's because at least some versions of OpenSSL are
 * too quick to report a write failure when there's still a possibility to
 * get a more useful error from the server.
 */
ssize_t
pqsecure_raw_write(PGconn *conn, const void *ptr, size_t len)
{
    ssize_t     n;
    int         flags = 0;
    int         result_errno = 0;
    char        msgbuf[1024];
    char        sebuf[PG_STRERROR_R_BUFLEN];
 
    DECLARE_SIGPIPE_INFO(spinfo);
 
    /*
     * If we already had a write failure, we will never again try to send data
     * on that connection.  Even if the kernel would let us, we've probably
     * lost message boundary sync with the server.  conn->write_failed
     * therefore persists until the connection is reset, and we just discard
     * all data presented to be written.
     */
    if (conn->write_failed)
        return len;
 
#ifdef MSG_NOSIGNAL
    if (conn->sigpipe_flag)
        flags |= MSG_NOSIGNAL;
 
retry_masked:
#endif                          /* MSG_NOSIGNAL */
 
    DISABLE_SIGPIPE(conn, spinfo, return -1);
 
    n = send(conn->sock, ptr, len, flags);
 
    if (n < 0)
    {
        result_errno = SOCK_ERRNO;
 
        /*
         * If we see an EINVAL, it may be because MSG_NOSIGNAL isn't available
         * on this machine.  So, clear sigpipe_flag so we don't try the flag
         * again, and retry the send().
         */
#ifdef MSG_NOSIGNAL
        if (flags != 0 && result_errno == EINVAL)
        {
            conn->sigpipe_flag = false;
            flags = 0;
            goto retry_masked;
        }
#endif                          /* MSG_NOSIGNAL */
 
        /* Set error message if appropriate */
        switch (result_errno)
        {
#ifdef EAGAIN
            case EAGAIN:
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
            case EWOULDBLOCK:
#endif
            case EINTR:
                /* no error message, caller is expected to retry */
                break;
 
            case EPIPE:
                /* Set flag for EPIPE */
                REMEMBER_EPIPE(spinfo, true);
 
                /* FALL THRU */
 
            case ECONNRESET:
                conn->write_failed = true;
                /* Store error message in conn->write_err_msg, if possible */
                /* (strdup failure is OK, we'll cope later) */
                snprintf(msgbuf, sizeof(msgbuf),
                         libpq_gettext("server closed the connection unexpectedly\n"
                                       "\tThis probably means the server terminated abnormally\n"
                                       "\tbefore or while processing the request."));
                /* keep newline out of translated string */
                strlcat(msgbuf, "\n", sizeof(msgbuf));
                conn->write_err_msg = strdup(msgbuf);
                /* Now claim the write succeeded */
                n = len;
                break;
 
            default:
                conn->write_failed = true;
                /* Store error message in conn->write_err_msg, if possible */
                /* (strdup failure is OK, we'll cope later) */
                snprintf(msgbuf, sizeof(msgbuf),
                         libpq_gettext("could not send data to server: %s"),
                         SOCK_STRERROR(result_errno,
                                       sebuf, sizeof(sebuf)));
                /* keep newline out of translated string */
                strlcat(msgbuf, "\n", sizeof(msgbuf));
                conn->write_err_msg = strdup(msgbuf);
                /* Now claim the write succeeded */
                n = len;
                break;
        }
    }
 
    RESTORE_SIGPIPE(conn, spinfo);
 
    /* ensure we return the intended errno to caller */
    SOCK_ERRNO_SET(result_errno);
 
    return n;
}
 
/* Dummy versions of SSL info functions, when built without SSL support */
#ifndef USE_SSL
 
void *
PQgetssl(PGconn *conn)
{
    return NULL;
}
 
void *
PQsslStruct(PGconn *conn, const char *struct_name)
{
    return NULL;
}
 
const char *
PQsslAttribute(PGconn *conn, const char *attribute_name)
{
    return NULL;
}
 
const char *const *
PQsslAttributeNames(PGconn *conn)
{
    static const char *const result[] = {NULL};
 
    return result;
}
#endif                          /* USE_SSL */
 
/*
 * Dummy versions of OpenSSL key password hook functions, when built without
 * OpenSSL.
 */
#ifndef USE_OPENSSL
 
PQsslKeyPassHook_OpenSSL_type
PQgetSSLKeyPassHook_OpenSSL(void)
{
    return NULL;
}
 
void
PQsetSSLKeyPassHook_OpenSSL(PQsslKeyPassHook_OpenSSL_type hook)
{
    return;
}
 
int
PQdefaultSSLKeyPassHook_OpenSSL(char *buf, int size, PGconn *conn)
{
    return 0;
}
#endif                          /* USE_OPENSSL */
 
/* Dummy version of GSSAPI information functions, when built without GSS support */
#ifndef ENABLE_GSS
 
void *
PQgetgssctx(PGconn *conn)
{
    return NULL;
}
 
int
PQgssEncInUse(PGconn *conn)
{
    return 0;
}
 
#endif                          /* ENABLE_GSS */
 
 
#if !defined(WIN32)
 
/*
 *  Block SIGPIPE for this thread.  This prevents send()/write() from exiting
 *  the application.
 */
int
pq_block_sigpipe(sigset_t *osigset, bool *sigpipe_pending)
{
    sigset_t    sigpipe_sigset;
    sigset_t    sigset;
 
    sigemptyset(&sigpipe_sigset);
    sigaddset(&sigpipe_sigset, SIGPIPE);
 
    /* Block SIGPIPE and save previous mask for later reset */
    SOCK_ERRNO_SET(pthread_sigmask(SIG_BLOCK, &sigpipe_sigset, osigset));
    if (SOCK_ERRNO)
        return -1;
 
    /* We can have a pending SIGPIPE only if it was blocked before */
    if (sigismember(osigset, SIGPIPE))
    {
        /* Is there a pending SIGPIPE? */
        if (sigpending(&sigset) != 0)
            return -1;
 
        if (sigismember(&sigset, SIGPIPE))
            *sigpipe_pending = true;
        else
            *sigpipe_pending = false;
    }
    else
        *sigpipe_pending = false;
 
    return 0;
}
 
/*
 *  Discard any pending SIGPIPE and reset the signal mask.
 *
 * Note: we are effectively assuming here that the C library doesn't queue
 * up multiple SIGPIPE events.  If it did, then we'd accidentally leave
 * ours in the queue when an event was already pending and we got another.
 * As long as it doesn't queue multiple events, we're OK because the caller
 * can't tell the difference.
 *
 * The caller should say got_epipe = false if it is certain that it
 * didn't get an EPIPE error; in that case we'll skip the clear operation
 * and things are definitely OK, queuing or no.  If it got one or might have
 * gotten one, pass got_epipe = true.
 *
 * We do not want this to change errno, since if it did that could lose
 * the error code from a preceding send().  We essentially assume that if
 * we were able to do pq_block_sigpipe(), this can't fail.
 */
void
pq_reset_sigpipe(sigset_t *osigset, bool sigpipe_pending, bool got_epipe)
{
    int         save_errno = SOCK_ERRNO;
    int         signo;
    sigset_t    sigset;
 
    /* Clear SIGPIPE only if none was pending */
    if (got_epipe && !sigpipe_pending)
    {
        if (sigpending(&sigset) == 0 &&
            sigismember(&sigset, SIGPIPE))
        {
            sigset_t    sigpipe_sigset;
 
            sigemptyset(&sigpipe_sigset);
            sigaddset(&sigpipe_sigset, SIGPIPE);
 
            sigwait(&sigpipe_sigset, &signo);
        }
    }
 
    /* Restore saved block mask */
    pthread_sigmask(SIG_SETMASK, osigset, NULL);
 
    SOCK_ERRNO_SET(save_errno);
}
 
#endif                          /* !WIN32 */