From patchwork Mon Jan 27 14:17:15 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Tokarev X-Patchwork-Id: 13951428 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CD3A0C0218A for ; Mon, 27 Jan 2025 14:19:21 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tcPwn-0008Om-PD; Mon, 27 Jan 2025 09:18:42 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tcPwN-0008KV-Ji; Mon, 27 Jan 2025 09:18:17 -0500 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tcPwL-0002J4-Hw; Mon, 27 Jan 2025 09:18:15 -0500 Received: from localhost.tls.msk.ru (mjt.wg.tls.msk.ru [192.168.177.130]) by isrv.corpit.ru (Postfix) with ESMTP id 21A64E0E27; Mon, 27 Jan 2025 17:17:39 +0300 (MSK) Received: by localhost.tls.msk.ru (Postfix, from userid 1000) id 5C08851D5F; Mon, 27 Jan 2025 17:18:03 +0300 (MSK) From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Christian Schoenebeck , Dirk Herrendorfer , Greg Kurz , Michael Tokarev Subject: [Stable-9.2.1 01/41] 9pfs: fix regression regarding CVE-2023-2861 Date: Mon, 27 Jan 2025 17:17:15 +0300 Message-Id: <20250127141803.3514882-1-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.5 In-Reply-To: References: MIME-Version: 1.0 Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Christian Schoenebeck The released fix for this CVE: f6b0de53fb8 ("9pfs: prevent opening special files (CVE-2023-2861)") caused a regression with security_model=passthrough. When handling a 'Tmknod' request there was a side effect that 'Tmknod' request could fail as 9p server was trying to adjust permissions: #6 close_if_special_file (fd=30) at ../hw/9pfs/9p-util.h:140 #7 openat_file (mode=, flags=2228224, name=, dirfd=) at ../hw/9pfs/9p-util.h:181 #8 fchmodat_nofollow (dirfd=dirfd@entry=31, name=name@entry=0x5555577ea6e0 "mysocket", mode=493) at ../hw/9pfs/9p-local.c:360 #9 local_set_cred_passthrough (credp=0x7ffbbc4ace10, name=0x5555577ea6e0 "mysocket", dirfd=31, fs_ctx=0x55555811f528) at ../hw/9pfs/9p-local.c:457 #10 local_mknod (fs_ctx=0x55555811f528, dir_path=, name=0x5555577ea6e0 "mysocket", credp=0x7ffbbc4ace10) at ../hw/9pfs/9p-local.c:702 #11 v9fs_co_mknod (pdu=pdu@entry=0x555558121140, fidp=fidp@entry=0x5555574c46c0, name=name@entry=0x7ffbbc4aced0, uid=1000, gid=1000, dev=, mode=49645, stbuf=0x7ffbbc4acef0) at ../hw/9pfs/cofs.c:205 #12 v9fs_mknod (opaque=0x555558121140) at ../hw/9pfs/9p.c:3711 That's because server was opening the special file to adjust permissions, however it was using O_PATH and it would have not returned the file descriptor to guest. So the call to close_if_special_file() on that branch was incorrect. Let's lift the restriction introduced by f6b0de53fb8 such that it would allow to open special files on host if O_PATH flag is supplied, not only for 9p server's own operations as described above, but also for any client 'Topen' request. It is safe to allow opening special files with O_PATH on host, because O_PATH only allows path based operations on the resulting file descriptor and prevents I/O such as read() and write() on that file descriptor. Fixes: f6b0de53fb8 ("9pfs: prevent opening special files (CVE-2023-2861)") Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2337 Reported-by: Dirk Herrendorfer Signed-off-by: Christian Schoenebeck Reviewed-by: Greg Kurz Tested-by: Dirk Herrendorfer Message-Id: (cherry picked from commit d06a9d843fb65351e0e4dc42ba0c404f01ea92b3) Signed-off-by: Michael Tokarev diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h index 51c94b0116..95ee4da9bd 100644 --- a/hw/9pfs/9p-util.h +++ b/hw/9pfs/9p-util.h @@ -177,20 +177,27 @@ again: return -1; } - if (close_if_special_file(fd) < 0) { - return -1; - } - - serrno = errno; - /* O_NONBLOCK was only needed to open the file. Let's drop it. We don't - * do that with O_PATH since fcntl(F_SETFL) isn't supported, and openat() - * ignored it anyway. - */ + /* Only if O_PATH is not set ... */ if (!(flags & O_PATH_9P_UTIL)) { + /* + * Prevent I/O on special files (device files, etc.) on host side, + * however it is safe and required to allow opening them with O_PATH, + * as this is limited to (required) path based operations only. + */ + if (close_if_special_file(fd) < 0) { + return -1; + } + + serrno = errno; + /* + * O_NONBLOCK was only needed to open the file. Let's drop it. We don't + * do that with O_PATH since fcntl(F_SETFL) isn't supported, and + * openat() ignored it anyway. + */ ret = fcntl(fd, F_SETFL, flags); assert(!ret); + errno = serrno; } - errno = serrno; return fd; }