From patchwork Mon Feb 21 21:25:13 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 12754144 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05A18C433EF for ; Mon, 21 Feb 2022 21:15:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234323AbiBUVPm (ORCPT ); Mon, 21 Feb 2022 16:15:42 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:41086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234293AbiBUVPl (ORCPT ); Mon, 21 Feb 2022 16:15:41 -0500 Received: from smtp-42ad.mail.infomaniak.ch (smtp-42ad.mail.infomaniak.ch [84.16.66.173]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D428923BE7 for ; Mon, 21 Feb 2022 13:15:13 -0800 (PST) Received: from smtp-2-0001.mail.infomaniak.ch (unknown [10.5.36.108]) by smtp-2-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4K2Znr2D7BzMqK3b; Mon, 21 Feb 2022 22:15:12 +0100 (CET) Received: from localhost (unknown [23.97.221.149]) by smtp-2-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4K2Znr0TjLzlhPJX; Mon, 21 Feb 2022 22:15:12 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: James Morris , "Serge E . Hallyn" Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Al Viro , Jann Horn , Kees Cook , Konstantin Meskhidze , Paul Moore , Shuah Khan , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= Subject: [PATCH v1 02/11] landlock: Reduce the maximum number of layers to 16 Date: Mon, 21 Feb 2022 22:25:13 +0100 Message-Id: <20220221212522.320243-3-mic@digikod.net> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220221212522.320243-1-mic@digikod.net> References: <20220221212522.320243-1-mic@digikod.net> MIME-Version: 1.0 Precedence: bulk List-ID: From: Mickaël Salaün The maximum number of nested Landlock domains is currently 64. Because of the following fix and to help reduce the stack size, let's reduce it to 16. This seems large enough for a lot of use cases (e.g. sandboxed init service, spawning a sandboxed SSH service, in nested sandboxed containers). Reducing the number of nested domains may also help to discover misuse of Landlock (e.g. creating a domain per rule). Add and use a dedicated layer_mask_t typedef to fit with the number of layers. This might be useful when changing it and to keep it consistent with the maximum number of layers. Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20220221212522.320243-3-mic@digikod.net Reviewed-by: Paul Moore --- security/landlock/fs.c | 13 +++++-------- security/landlock/limits.h | 2 +- security/landlock/ruleset.h | 4 ++++ tools/testing/selftests/landlock/fs_test.c | 2 +- 4 files changed, 11 insertions(+), 10 deletions(-) diff --git a/security/landlock/fs.c b/security/landlock/fs.c index 9de2a460a762..4048e3c04d75 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -180,10 +180,10 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, /* Access-control management */ -static inline u64 unmask_layers( +static inline layer_mask_t unmask_layers( const struct landlock_ruleset *const domain, const struct path *const path, - const access_mask_t access_request, u64 layer_mask) + const access_mask_t access_request, layer_mask_t layer_mask) { const struct landlock_rule *rule; const struct inode *inode; @@ -209,11 +209,11 @@ static inline u64 unmask_layers( */ for (i = 0; i < rule->num_layers; i++) { const struct landlock_layer *const layer = &rule->layers[i]; - const u64 layer_level = BIT_ULL(layer->level - 1); + const layer_mask_t layer_bit = BIT_ULL(layer->level - 1); /* Checks that the layer grants access to the full request. */ if ((layer->access & access_request) == access_request) { - layer_mask &= ~layer_level; + layer_mask &= ~layer_bit; if (layer_mask == 0) return layer_mask; @@ -228,12 +228,9 @@ static int check_access_path(const struct landlock_ruleset *const domain, { bool allowed = false; struct path walker_path; - u64 layer_mask; + layer_mask_t layer_mask; size_t i; - /* Make sure all layers can be checked. */ - BUILD_BUG_ON(BITS_PER_TYPE(layer_mask) < LANDLOCK_MAX_NUM_LAYERS); - if (!access_request) return 0; if (WARN_ON_ONCE(!domain || !path)) diff --git a/security/landlock/limits.h b/security/landlock/limits.h index 458d1de32ed5..126d1ec04d34 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -13,7 +13,7 @@ #include #include -#define LANDLOCK_MAX_NUM_LAYERS 64 +#define LANDLOCK_MAX_NUM_LAYERS 16 #define LANDLOCK_MAX_NUM_RULES U32_MAX #define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_MAKE_SYM diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h index 7e7cac68e443..0128c56ee7ff 100644 --- a/security/landlock/ruleset.h +++ b/security/landlock/ruleset.h @@ -23,6 +23,10 @@ typedef u16 access_mask_t; /* Makes sure all filesystem access rights can be stored. */ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS); +typedef u16 layer_mask_t; +/* Makes sure all layers can be checked. */ +static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS); + /** * struct landlock_layer - Access rights for a given layer */ diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index 10c9a1e4ebd9..99838cac970b 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -1080,7 +1080,7 @@ TEST_F_FORK(layout1, max_layers) const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); ASSERT_LE(0, ruleset_fd); - for (i = 0; i < 64; i++) + for (i = 0; i < 16; i++) enforce_ruleset(_metadata, ruleset_fd); for (i = 0; i < 2; i++) {