From: Jann Horn <jannh@google.com> To: "Mickaël Salaün" <mic@digikod.net> Cc: "James Morris" <jmorris@namei.org>, "Serge E . Hallyn" <serge@hallyn.com>, "Al Viro" <viro@zeniv.linux.org.uk>, "Andy Lutomirski" <luto@amacapital.net>, "Anton Ivanov" <anton.ivanov@cambridgegreys.com>, "Arnd Bergmann" <arnd@arndb.de>, "Casey Schaufler" <casey@schaufler-ca.com>, "Jeff Dike" <jdike@addtoit.com>, "Jonathan Corbet" <corbet@lwn.net>, "Kees Cook" <keescook@chromium.org>, "Michael Kerrisk" <mtk.manpages@gmail.com>, "Richard Weinberger" <richard@nod.at>, "Shuah Khan" <shuah@kernel.org>, "Vincent Dagonneau" <vincent.dagonneau@ssi.gouv.fr>, "Kernel Hardening" <kernel-hardening@lists.openwall.com>, "Linux API" <linux-api@vger.kernel.org>, linux-arch <linux-arch@vger.kernel.org>, "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, "kernel list" <linux-kernel@vger.kernel.org>, "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>, linux-security-module <linux-security-module@vger.kernel.org>, "the arch/x86 maintainers" <x86@kernel.org>, "Mickaël Salaün" <mic@linux.microsoft.com> Subject: Re: [PATCH v26 07/12] landlock: Support filesystem access-control Date: Thu, 14 Jan 2021 04:22:01 +0100 Message-ID: <CAG48ez1wbAQwU-eoC9DngHyUM_5F01MJQpRnLaJFvfRUrnXBdA@mail.gmail.com> (raw) In-Reply-To: <20201209192839.1396820-8-mic@digikod.net> On Wed, Dec 9, 2020 at 8:28 PM Mickaël Salaün <mic@digikod.net> wrote: > Thanks to the Landlock objects and ruleset, it is possible to identify > inodes according to a process's domain. To enable an unprivileged > process to express a file hierarchy, it first needs to open a directory > (or a file) and pass this file descriptor to the kernel through > landlock_add_rule(2). When checking if a file access request is > allowed, we walk from the requested dentry to the real root, following > the different mount layers. The access to each "tagged" inodes are > collected according to their rule layer level, and ANDed to create > access to the requested file hierarchy. This makes possible to identify > a lot of files without tagging every inodes nor modifying the > filesystem, while still following the view and understanding the user > has from the filesystem. > > Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not > keep the same struct inodes for the same inodes whereas these inodes are > in use. > > This commit adds a minimal set of supported filesystem access-control > which doesn't enable to restrict all file-related actions. This is the > result of multiple discussions to minimize the code of Landlock to ease > review. Thanks to the Landlock design, extending this access-control > without breaking user space will not be a problem. Moreover, seccomp > filters can be used to restrict the use of syscall families which may > not be currently handled by Landlock. [...] > +static bool check_access_path_continue( > + const struct landlock_ruleset *const domain, > + const struct path *const path, const u32 access_request, > + u64 *const layer_mask) > +{ [...] > + /* > + * An access is granted if, for each policy layer, at least one rule > + * encountered on the pathwalk grants the access, regardless of their > + * position in the layer stack. We must then check not-yet-seen layers > + * for each inode, from the last one added to the first one. > + */ > + 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); > + > + if (!(layer_level & *layer_mask)) > + continue; > + if ((layer->access & access_request) != access_request) > + return false; > + *layer_mask &= ~layer_level; Hmm... shouldn't the last 5 lines be replaced by the following? if ((layer->access & access_request) == access_request) *layer_mask &= ~layer_level; And then, since this function would always return true, you could change its return type to "void". As far as I can tell, the current version will still, if a ruleset looks like this: /usr read+write /usr/lib/ read reject write access to /usr/lib, right? > + } > + return true; > +}
next prev parent reply index Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-09 19:28 [PATCH v26 00/12] Landlock LSM Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 01/12] landlock: Add object management Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 02/12] landlock: Add ruleset and domain management Mickaël Salaün 2021-01-14 3:21 ` Jann Horn 2020-12-09 19:28 ` [PATCH v26 03/12] landlock: Set up the security framework and manage credentials Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 04/12] landlock: Add ptrace restrictions Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 05/12] LSM: Infrastructure management of the superblock Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 06/12] fs,security: Add sb_delete hook Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 07/12] landlock: Support filesystem access-control Mickaël Salaün 2021-01-14 3:22 ` Jann Horn [this message] 2021-01-14 18:54 ` Mickaël Salaün 2021-01-14 22:43 ` Jann Horn 2021-01-15 9:10 ` Mickaël Salaün 2021-01-15 18:31 ` Jann Horn 2021-01-16 17:16 ` Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 08/12] landlock: Add syscall implementations Mickaël Salaün 2020-12-10 10:38 ` Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 09/12] arch: Wire up Landlock syscalls Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 10/12] selftests/landlock: Add user space tests Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 11/12] samples/landlock: Add a sandbox manager example Mickaël Salaün 2021-01-14 3:21 ` Jann Horn 2021-01-14 18:59 ` Mickaël Salaün 2020-12-09 19:28 ` [PATCH v26 12/12] landlock: Add user and kernel documentation Mickaël Salaün 2021-01-14 3:22 ` [PATCH v26 00/12] Landlock LSM Jann Horn 2021-01-14 19:03 ` Mickaël Salaün
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