From patchwork Fri May 28 09:24:16 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 12286497 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0BAAEC4708D for ; Fri, 28 May 2021 09:27:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E769D613AB for ; Fri, 28 May 2021 09:26:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235493AbhE1J2a (ORCPT ); Fri, 28 May 2021 05:28:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:52886 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230200AbhE1J23 (ORCPT ); Fri, 28 May 2021 05:28:29 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6A2CB6127A; Fri, 28 May 2021 09:26:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1622194014; bh=n7L8THJ3hgZnP0QknCDp3CNVsn2J9iLiP7bBjnxa8/c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=F8nGVd+7W0rKD5PftV8egcAMuatHe4J+OZtYV19FwqQFAHfZquYE+leRb2IC3gYvt wOXn7EHa6rjwWcmK6TrQpigfUZf+gLjjMkJsfMyWE+pmE0P2AP3b/62Q3dDFpJNdw9 dcE4j5IheFRI35++VXbGxNacmwkaA9um4dZVNobg3B8dyDSRlUPvWUbcXaS43M70GM 2LnW4SEBEG4uRn+hNToRpWpSADwYZ+FE+h/f/CxEudyG7VRNGRsXaFZGUkI2rev30N gKsI2RszmhHxAEdtWNcPE/q8lHPhdbRm5YUTzhC6UBe19EV4R8/RWXCxrj4vqjDRgq 9Cf5lEa8vMGGQ== From: Christian Brauner To: Christoph Hellwig , Al Viro Cc: Aleksa Sarai , Richard Guy Briggs , linux-fsdevel@vger.kernel.org, Christian Brauner Subject: [PATCH v2 2/3] open: don't silently ignore unknown O-flags in openat2() Date: Fri, 28 May 2021 11:24:16 +0200 Message-Id: <20210528092417.3942079-3-brauner@kernel.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210528092417.3942079-1-brauner@kernel.org> References: <20210528092417.3942079-1-brauner@kernel.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; i=6HfI8flciKZB4VJnvGhErn3MBardNcPBqXfs5h/OfHw=; m=/i3HZZPKrmP04P+3mxM9YAOUPpHgr0g11FybAeMMEik=; p=NhmB7D6ZKh509a1KOnsYyxxVfeBSiBZ7igGZNN3BR3g=; g=de67de0e05d85c0da892ea52f4de0f5e1b5519a9 X-Patch-Sig: m=pgp; i=christian.brauner@ubuntu.com; s=0x0x91C61BC06578DCA2; b=iHUEABYKAB0WIQRAhzRXHqcMeLMyaSiRxhvAZXjcogUCYLC2egAKCRCRxhvAZXjcoij8AP9XPXl 44vksthPj4/+j9WHtdJ1Q8xK0S4MBt28P7cKEiwEAv5nt5d97XgTj97gtcPjyKTatf7xQsth/Ts8y sJGXCgI= Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Christian Brauner The new openat2() syscall verifies that no unknown O-flag values are set and returns an error to userspace if they are while the older open syscalls like open() and openat() simply ignore unknown flag values: #define O_FLAG_CURRENTLY_INVALID (1 << 31) struct open_how how = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID, .resolve = 0, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how, sizeof(how)); /* succeeds */ fd = openat(-EBADF, "/dev/null", O_RDONLY | O_FLAG_CURRENTLY_INVALID); However, openat2() silently truncates the upper 32 bits meaning: #define O_FLAG_CURRENTLY_INVALID_LOWER32 (1 << 31) #define O_FLAG_CURRENTLY_INVALID_UPPER32 (1 << 40) struct open_how how_lowe32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_LOWER32, }; struct open_how how_upper32 = { .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_UPPER32, }; /* fails */ fd = openat2(-EBADF, "/dev/null", &how_lower32, sizeof(how_lower32)); /* succeeds */ fd = openat2(-EBADF, "/dev/null", &how_upper32, sizeof(how_upper32)); Fix this by preventing the immediate truncation in build_open_flags(). There's a snafu here though stripping FMODE_* directly from flags would cause the upper 32 bits to be truncated as well due to integer promotion rules since FMODE_* is unsigned int, O_* are signed ints (yuck). In addition, struct open_flags currently defines flags to be 32 bit which is reasonable. If we simply were to bump it to 64 bit we would need to change a lot of code preemptively which doesn't seem worth it. So simply add a compile-time check verifying that all currently known O_* flags are within the 32 bit range and fail to build if they aren't anymore. This change shouldn't regress old open syscalls since they silently truncate any unknown values anyway. It is a tiny semantic change for openat2() but it is very unlikely people pass ing > 32 bit unknown flags and the syscall is relatively new too. Cc: Christoph Hellwig Cc: Aleksa Sarai Cc: Al Viro Cc: linux-fsdevel@vger.kernel.org Reported-by: Richard Guy Briggs Reviewed-by: Christoph Hellwig Reviewed-by: Aleksa Sarai Signed-off-by: Christian Brauner Reviewed-by: Richard Guy Briggs --- /* v2 */ - Richard Guy Briggs : - Add an explicit BUILD_BUG_ON() to check when we need to change struct open_flags to account for O_* flags > 32 bits. --- fs/open.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/open.c b/fs/open.c index e53af13b5835..53bc0573c0ec 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1002,12 +1002,20 @@ inline struct open_how build_open_how(int flags, umode_t mode) inline int build_open_flags(const struct open_how *how, struct open_flags *op) { - int flags = how->flags; + u64 flags = how->flags; + u64 strip = FMODE_NONOTIFY | O_CLOEXEC; int lookup_flags = 0; int acc_mode = ACC_MODE(flags); - /* Must never be set by userspace */ - flags &= ~(FMODE_NONOTIFY | O_CLOEXEC); + BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS), + "struct open_flags doesn't yet handle flags > 32 bits"); + + /* + * Strip flags that either shouldn't be set by userspace like + * FMODE_NONOTIFY or that aren't relevant in determining struct + * open_flags like O_CLOEXEC. + */ + flags &= ~strip; /* * Older syscalls implicitly clear all of the invalid flags or argument