fe-secure-common.c

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/*-------------------------------------------------------------------------
 *
 * fe-secure-common.c
 *
 * common implementation-independent SSL support code
 *
 * While fe-secure.c contains the interfaces that the rest of libpq call, this
 * file contains support routines that are used by the library-specific
 * implementations such as fe-secure-openssl.c.
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-secure-common.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <arpa/inet.h>
 
#include "fe-secure-common.h"
 
#include "libpq-int.h"
#include "pqexpbuffer.h"
 
/*
 * Check if a wildcard certificate matches the server hostname.
 *
 * The rule for this is:
 *  1. We only match the '*' character as wildcard
 *  2. We match only wildcards at the start of the string
 *  3. The '*' character does *not* match '.', meaning that we match only
 *     a single pathname component.
 *  4. We don't support more than one '*' in a single pattern.
 *
 * This is roughly in line with RFC2818, but contrary to what most browsers
 * appear to be implementing (point 3 being the difference)
 *
 * Matching is always case-insensitive, since DNS is case insensitive.
 */
static bool
wildcard_certificate_match(const char *pattern, const char *string)
{
    int         lenpat = strlen(pattern);
    int         lenstr = strlen(string);
 
    /* If we don't start with a wildcard, it's not a match (rule 1 & 2) */
    if (lenpat < 3 ||
        pattern[0] != '*' ||
        pattern[1] != '.')
        return false;
 
    /* If pattern is longer than the string, we can never match */
    if (lenpat > lenstr)
        return false;
 
    /*
     * If string does not end in pattern (minus the wildcard), we don't match
     */
    if (pg_strcasecmp(pattern + 1, string + lenstr - lenpat + 1) != 0)
        return false;
 
    /*
     * If there is a dot left of where the pattern started to match, we don't
     * match (rule 3)
     */
    if (strchr(string, '.') < string + lenstr - lenpat)
        return false;
 
    /* String ended with pattern, and didn't have a dot before, so we match */
    return true;
}
 
/*
 * Check if a name from a server's certificate matches the peer's hostname.
 *
 * Returns 1 if the name matches, and 0 if it does not. On error, returns
 * -1, and sets the libpq error message.
 *
 * The name extracted from the certificate is returned in *store_name. The
 * caller is responsible for freeing it.
 */
int
pq_verify_peer_name_matches_certificate_name(PGconn *conn,
                                             const char *namedata, size_t namelen,
                                             char **store_name)
{
    char       *name;
    int         result;
    char       *host = conn->connhost[conn->whichhost].host;
 
    *store_name = NULL;
 
    if (!(host && host[0] != '\0'))
    {
        libpq_append_conn_error(conn, "host name must be specified");
        return -1;
    }
 
    /*
     * There is no guarantee the string returned from the certificate is
     * NULL-terminated, so make a copy that is.
     */
    name = malloc(namelen + 1);
    if (name == NULL)
    {
        libpq_append_conn_error(conn, "out of memory");
        return -1;
    }
    memcpy(name, namedata, namelen);
    name[namelen] = '\0';
 
    /*
     * Reject embedded NULLs in certificate common or alternative name to
     * prevent attacks like CVE-2009-4034.
     */
    if (namelen != strlen(name))
    {
        free(name);
        libpq_append_conn_error(conn, "SSL certificate's name contains embedded null");
        return -1;
    }
 
    if (pg_strcasecmp(name, host) == 0)
    {
        /* Exact name match */
        result = 1;
    }
    else if (wildcard_certificate_match(name, host))
    {
        /* Matched wildcard name */
        result = 1;
    }
    else
    {
        result = 0;
    }
 
    *store_name = name;
    return result;
}
 
/*
 * Check if an IP address from a server's certificate matches the peer's
 * hostname (which must itself be an IPv4/6 address).
 *
 * Returns 1 if the address matches, and 0 if it does not. On error, returns
 * -1, and sets the libpq error message.
 *
 * A string representation of the certificate's IP address is returned in
 * *store_name. The caller is responsible for freeing it.
 */
int
pq_verify_peer_name_matches_certificate_ip(PGconn *conn,
                                           const unsigned char *ipdata,
                                           size_t iplen,
                                           char **store_name)
{
    char       *addrstr;
    int         match = 0;
    char       *host = conn->connhost[conn->whichhost].host;
    int         family;
    char        tmp[sizeof "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255"];
    char        sebuf[PG_STRERROR_R_BUFLEN];
 
    *store_name = NULL;
 
    if (!(host && host[0] != '\0'))
    {
        libpq_append_conn_error(conn, "host name must be specified");
        return -1;
    }
 
    /*
     * The data from the certificate is in network byte order. Convert our
     * host string to network-ordered bytes as well, for comparison. (The host
     * string isn't guaranteed to actually be an IP address, so if this
     * conversion fails we need to consider it a mismatch rather than an
     * error.)
     */
    if (iplen == 4)
    {
        /* IPv4 */
        struct in_addr addr;
 
        family = AF_INET;
 
        /*
         * The use of inet_aton() is deliberate; we accept alternative IPv4
         * address notations that are accepted by inet_aton() but not
         * inet_pton() as server addresses.
         */
        if (inet_aton(host, &addr))
        {
            if (memcmp(ipdata, &addr.s_addr, iplen) == 0)
                match = 1;
        }
    }
 
    /*
     * If they don't have inet_pton(), skip this.  Then, an IPv6 address in a
     * certificate will cause an error.
     */
#ifdef HAVE_INET_PTON
    else if (iplen == 16)
    {
        /* IPv6 */
        struct in6_addr addr;
 
        family = AF_INET6;
 
        if (inet_pton(AF_INET6, host, &addr) == 1)
        {
            if (memcmp(ipdata, &addr.s6_addr, iplen) == 0)
                match = 1;
        }
    }
#endif
    else
    {
        /*
         * Not IPv4 or IPv6. We could ignore the field, but leniency seems
         * wrong given the subject matter.
         */
        libpq_append_conn_error(conn, "certificate contains IP address with invalid length %zu",
                                iplen);
        return -1;
    }
 
    /* Generate a human-readable representation of the certificate's IP. */
    addrstr = pg_inet_net_ntop(family, ipdata, 8 * iplen, tmp, sizeof(tmp));
    if (!addrstr)
    {
        libpq_append_conn_error(conn, "could not convert certificate's IP address to string: %s",
                                strerror_r(errno, sebuf, sizeof(sebuf)));
        return -1;
    }
 
    *store_name = strdup(addrstr);
    return match;
}
 
/*
 * Verify that the server certificate matches the hostname we connected to.
 *
 * The certificate's Common Name and Subject Alternative Names are considered.
 */
bool
pq_verify_peer_name_matches_certificate(PGconn *conn)
{
    char       *host = conn->connhost[conn->whichhost].host;
    int         rc;
    int         names_examined = 0;
    char       *first_name = NULL;
 
    /*
     * If told not to verify the peer name, don't do it. Return true
     * indicating that the verification was successful.
     */
    if (strcmp(conn->sslmode, "verify-full") != 0)
        return true;
 
    /* Check that we have a hostname to compare with. */
    if (!(host && host[0] != '\0'))
    {
        libpq_append_conn_error(conn, "host name must be specified for a verified SSL connection");
        return false;
    }
 
    rc = pgtls_verify_peer_name_matches_certificate_guts(conn, &names_examined, &first_name);
 
    if (rc == 0)
    {
        /*
         * No match. Include the name from the server certificate in the error
         * message, to aid debugging broken configurations. If there are
         * multiple names, only print the first one to avoid an overly long
         * error message.
         */
        if (names_examined > 1)
        {
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_ngettext("server certificate for \"%s\" (and %d other name) does not match host name \"%s\"",
                                             "server certificate for \"%s\" (and %d other names) does not match host name \"%s\"",
                                             names_examined - 1),
                              first_name, names_examined - 1, host);
            appendPQExpBufferChar(&conn->errorMessage, '\n');
        }
        else if (names_examined == 1)
        {
            libpq_append_conn_error(conn, "server certificate for \"%s\" does not match host name \"%s\"",
                                    first_name, host);
        }
        else
        {
            libpq_append_conn_error(conn, "could not get server's host name from server certificate");
        }
    }
 
    /* clean up */
    free(first_name);
 
    return (rc == 1);
}