From patchwork Wed Oct 9 20:40:42 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Aleksa Sarai X-Patchwork-Id: 13829237 Received: from mout-p-201.mailbox.org (mout-p-201.mailbox.org [80.241.56.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D9AC1E7C3E; Wed, 9 Oct 2024 20:42:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.171 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728506552; cv=none; b=lROuajdjjudj3CKmxCdHZMCjb8U01UWVgSgFCHEc4fB4dulbKAakwGdJNQIzcgeLvwZvUKaGT1puvE63aYiqqCO/X3c/TerfNR65Df3g1avJXCP1QkVAlc0zQohiO1jlqHUKQvEvpUfUg94G18J7oc7xWUOHun1wROtr1qkktkw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728506552; c=relaxed/simple; bh=uMJLkf5QTDuvdiBzRMepbN6IKFXf5n7a7YM4+FwWbAk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=s1vUdknFbtyK87O4FKY9cXmfyI+Y66fCzTFsXn2WSbHhKF2zk6LwXtzMJpqONge6TWIj0ccEfrNpc0Ia/nXvmpJq/WPs0nXlV/TVOJkcX37p8WV7waF/94ZJUJcGnHU/Cb973ndHB7e4uzDW2OPBtwZnJ4frDL9y8HszIUuWyvE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=cyphar.com; spf=pass smtp.mailfrom=cyphar.com; dkim=pass (2048-bit key) header.d=cyphar.com header.i=@cyphar.com header.b=ZjNZHALZ; arc=none smtp.client-ip=80.241.56.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=cyphar.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=cyphar.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=cyphar.com header.i=@cyphar.com header.b="ZjNZHALZ" Received: from smtp102.mailbox.org (smtp102.mailbox.org [IPv6:2001:67c:2050:b231:465::102]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-201.mailbox.org (Postfix) with ESMTPS id 4XP4ZW0rLNz9ssh; Wed, 9 Oct 2024 22:42:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cyphar.com; s=MBO0001; t=1728506547; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QWYXRXXrADdO6m0g06MFjKfnGjcDChbWetducV/F6Dk=; b=ZjNZHALZWFcrjZgV9gAg0JNFBkQlLD2SaCQY1YF2e9E23GDiBLPflEaL4boR0gyEkEggy9 XLW0KNc2DSCBqByqxm4hir/o531UXgDTzDdW7RM3USRTyWq/7xWwMLdzLltrlm2iwi+xTu dnI8SqSL6O5KB6eaScMcP/O4DqJpN835gz5ToETv3Stveq+0CsK/knfKzpL9OLNz8np2nx Izz2LyEEKAxM1VpL1PSxeaTLgF8JS7uPy79iP8fjiq7LCGE5FXFXgkplKUkOJhJDXe01N9 4XTdDzNYLqSzB8r/MefbtcWeIDTSPyv1RKHwKOzF4mQYmaWFpCURYPQExJqO8Q== From: Aleksa Sarai Date: Thu, 10 Oct 2024 07:40:42 +1100 Subject: [PATCH RFC v3 09/10] mount_setattr: add CHECK_FIELDS flag to usize argument Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241010-extensible-structs-check_fields-v3-9-d2833dfe6edd@cyphar.com> References: <20241010-extensible-structs-check_fields-v3-0-d2833dfe6edd@cyphar.com> In-Reply-To: <20241010-extensible-structs-check_fields-v3-0-d2833dfe6edd@cyphar.com> To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Alexander Viro , Christian Brauner , Jan Kara , Arnd Bergmann , Shuah Khan Cc: Kees Cook , Florian Weimer , Arnd Bergmann , Mark Rutland , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, Aleksa Sarai X-Developer-Signature: v=1; a=openpgp-sha256; l=2453; i=cyphar@cyphar.com; h=from:subject:message-id; bh=uMJLkf5QTDuvdiBzRMepbN6IKFXf5n7a7YM4+FwWbAk=; b=owGbwMvMwCWmMf3Xpe0vXfIZT6slMaSzvQp6eOwQr3GCiIjonTCWo6sOZps53Up4lHl7G8OVC 9vY+Q5c7ChlYRDjYpAVU2TZ5ucZumn+4ivJn1aywcxhZQIZwsDFKQATeeDB8D/p0qE1VzfuzLXq 9HnMcv/w/70FyysO/284OdtAa9PfgsiVDP9snyots6z2r8j6EH89oeyRSUzpmdfTUz3VXkrl3as NsWYEAA== X-Developer-Key: i=cyphar@cyphar.com; a=openpgp; fpr=C9C370B246B09F6DBCFC744C34401015D1D2D386 X-Rspamd-Queue-Id: 4XP4ZW0rLNz9ssh As with openat2(2), this allows userspace to easily figure out what flags and fields are supported by mount_setattr(2). As with clone3(2), for fields which are not flag-based, we simply set every bit in the field so that a naive bitwise-and would show that any value of the field is valid. The intended way of using this interface to get feature information looks something like the following: static bool mountattr_nosymfollow_supported; static bool mountattr_idmap_supported; int check_clone3_support(void) { int err; struct mount_attr attr = {}; err = mount_attr(-EBADF, "", 0, &args, CHECK_FIELDS | sizeof(args)); assert(err < 0); switch (errno) { case EFAULT: case E2BIG: /* Old kernel... */ check_support_the_old_way(); break; case EEXTSYS_NOOP: mountattr_nosymfollow_supported = ((attr.attr_clr | attr.attr_set) & MOUNT_ATTR_NOSYMFOLLOW); mountattr_idmap_supported = ((attr.attr_clr | attr.attr_set) & MOUNT_ATTR_IDMAP) && (attr.userns_fd != 0); break; } } Signed-off-by: Aleksa Sarai --- fs/namespace.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 328087a4df8a..c7ae8d96b7b7 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4771,6 +4771,7 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, size_t, usize) { int err; + bool check_fields; struct path target; struct mount_attr attr; struct mount_kattr kattr; @@ -4783,11 +4784,27 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, AT_NO_AUTOMOUNT)) return -EINVAL; + check_fields = usize & CHECK_FIELDS; + usize &= ~CHECK_FIELDS; + if (unlikely(usize > PAGE_SIZE)) return -E2BIG; if (unlikely(usize < MOUNT_ATTR_SIZE_VER0)) return -EINVAL; + if (unlikely(check_fields)) { + memset(&attr, 0, sizeof(attr)); + attr = (struct mount_attr) { + .attr_set = MOUNT_SETATTR_VALID_FLAGS, + .attr_clr = MOUNT_SETATTR_VALID_FLAGS, + .propagation = MOUNT_SETATTR_PROPAGATION_FLAGS, + .userns_fd = 0xFFFFFFFFFFFFFFFF, + }; + + err = copy_struct_to_user(uattr, usize, &attr, sizeof(attr), NULL); + return err ?: -EEXTSYS_NOOP; + } + if (!may_mount()) return -EPERM;