Commit message: CVE-2015-5296: s3:libsmb: force signing when requiring encryption in SMBC_server_internal()

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11536

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
CVE: CVE-2015-5296
CWE: CWE-20
Vulnerability description: Samba 3.x and 4.x before 4.1.22, 4.2.x before 4.2.7, and 4.3.x before 4.3.3 supports connections that are encrypted but unsigned, which allows man-in-the-middle attackers to conduct encrypted-to-unencrypted downgrade attacks by modifying the client-server data stream, related to clidfs.c, libsmb_server.c, and smbXcli_base.c.

Project: samba

SMBC_server_internal(TALLOC_CTX *ctx,
            SMBCCTX *context,
            bool connect_if_not_found,
            const char *server,
            uint16_t port,
            const char *share,
            char **pp_workgroup,
            char **pp_username,
            char **pp_password,
	    bool *in_cache)
{
	SMBCSRV *srv=NULL;
	char *workgroup = NULL;
	struct cli_state *c = NULL;
	const char *server_n = server;
        int is_ipc = (share != NULL && strcmp(share, "IPC$") == 0);
	uint32_t fs_attrs = 0;
        const char *username_used;
 	NTSTATUS status;
        char *newserver, *newshare;
        int flags = 0;
        struct smbXcli_tcon *tcon = NULL;
 
        ZERO_STRUCT(c);
        *in_cache = false;
	if (server[0] == 0) {
		errno = EPERM;
		return NULL;
	}

        /* Look for a cached connection */
        srv = SMBC_find_server(ctx, context, server, share,
                               pp_workgroup, pp_username, pp_password);

        /*
         * If we found a connection and we're only allowed one share per
         * server...
         */
        if (srv &&
	    share != NULL && *share != '\0' &&
            smbc_getOptionOneSharePerServer(context)) {

                /*
                 * ... then if there's no current connection to the share,
                 * connect to it.  SMBC_find_server(), or rather the function
                 * pointed to by context->get_cached_srv_fn which
                 * was called by SMBC_find_server(), will have issued a tree
                 * disconnect if the requested share is not the same as the
                 * one that was already connected.
                 */

		/*
		 * Use srv->cli->desthost and srv->cli->share instead of
		 * server and share below to connect to the actual share,
		 * i.e., a normal share or a referred share from
		 * 'msdfs proxy' share.
		 */
                if (!cli_state_has_tcon(srv->cli)) {
                        /* Ensure we have accurate auth info */
			SMBC_call_auth_fn(ctx, context,
					  smbXcli_conn_remote_name(srv->cli->conn),
					  srv->cli->share,
                                          pp_workgroup,
                                          pp_username,
                                          pp_password);

			if (!*pp_workgroup || !*pp_username || !*pp_password) {
				errno = ENOMEM;
				cli_shutdown(srv->cli);
				srv->cli = NULL;
				smbc_getFunctionRemoveCachedServer(context)(context,
                                                                            srv);
				return NULL;
			}

			/*
			 * We don't need to renegotiate encryption
			 * here as the encryption context is not per
			 * tid.
			 */

			status = cli_tree_connect(srv->cli,
						  srv->cli->share,
						  "?????",
						  *pp_password,
						  strlen(*pp_password)+1);
			if (!NT_STATUS_IS_OK(status)) {
                                errno = map_errno_from_nt_status(status);
                                cli_shutdown(srv->cli);
				srv->cli = NULL;
                                smbc_getFunctionRemoveCachedServer(context)(context,
                                                                            srv);
                                srv = NULL;
                        }

                        /* Determine if this share supports case sensitivity */
                        if (is_ipc) {
                                DEBUG(4,
                                      ("IPC$ so ignore case sensitivity\n"));
                                status = NT_STATUS_OK;
                        } else {
                                status = cli_get_fs_attr_info(c, &fs_attrs);
                        }

                        if (!NT_STATUS_IS_OK(status)) {
                                DEBUG(4, ("Could not retrieve "
                                          "case sensitivity flag: %s.\n",
                                          nt_errstr(status)));

                                /*
                                 * We can't determine the case sensitivity of
                                 * the share. We have no choice but to use the
                                 * user-specified case sensitivity setting.
                                 */
                                if (smbc_getOptionCaseSensitive(context)) {
                                        cli_set_case_sensitive(c, True);
                                } else {
                                        cli_set_case_sensitive(c, False);
                                }
                        } else if (!is_ipc) {
                                DEBUG(4,
                                      ("Case sensitive: %s\n",
                                       (fs_attrs & FILE_CASE_SENSITIVE_SEARCH
                                        ? "True"
                                        : "False")));
                                cli_set_case_sensitive(
                                        c,
                                        (fs_attrs & FILE_CASE_SENSITIVE_SEARCH
                                         ? True
                                         : False));
                        }

                        /*
                         * Regenerate the dev value since it's based on both
                         * server and share
                         */
                        if (srv) {
				const char *remote_name =
					smbXcli_conn_remote_name(srv->cli->conn);

				srv->dev = (dev_t)(str_checksum(remote_name) ^
                                                   str_checksum(srv->cli->share));
                        }
                }
        }

        /* If we have a connection... */
        if (srv) {

                /* ... then we're done here.  Give 'em what they came for. */
		*in_cache = true;
                goto done;
        }

        /* If we're not asked to connect when a connection doesn't exist... */
        if (! connect_if_not_found) {
                /* ... then we're done here. */
                return NULL;
        }

	if (!*pp_workgroup || !*pp_username || !*pp_password) {
		errno = ENOMEM;
		return NULL;
	}

	DEBUG(4,("SMBC_server: server_n=[%s] server=[%s]\n", server_n, server));

	DEBUG(4,(" -> server_n=[%s] server=[%s]\n", server_n, server));

	status = NT_STATUS_UNSUCCESSFUL;

	if (smbc_getOptionUseKerberos(context)) {
		flags |= CLI_FULL_CONNECTION_USE_KERBEROS;
	}

	if (smbc_getOptionFallbackAfterKerberos(context)) {
		flags |= CLI_FULL_CONNECTION_FALLBACK_AFTER_KERBEROS;
	}

	if (smbc_getOptionUseCCache(context)) {
		flags |= CLI_FULL_CONNECTION_USE_CCACHE;
	}

	if (smbc_getOptionUseNTHash(context)) {
		flags |= CLI_FULL_CONNECTION_USE_NT_HASH;
                flags |= CLI_FULL_CONNECTION_USE_NT_HASH;
        }
 
        if (port == 0) {
                if (share == NULL || *share == '\0' || is_ipc) {
                        /*
		}
                         */
                        status = cli_connect_nb(server_n, NULL, NBT_SMB_PORT, 0x20,
                                        smbc_getNetbiosName(context),
                                       SMB_SIGNING_DEFAULT, flags, &c);
                }
        }