From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-42aa.mail.infomaniak.ch (smtp-42aa.mail.infomaniak.ch [84.16.66.170]) (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 4A39518CC05 for ; Thu, 8 Aug 2024 14:09:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=84.16.66.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723126178; cv=none; b=aa1Nr/uXGRyZi+xAlREGQ2qglmysmfVYPzd0dqyB4RaxGK7F0EL/jGGkRbAjKKLY/PZMKnYEH28MDMVxaDqTwGlP5A07mweMdaOGfshi4537eG5AOI8ZfWP+uXgWhoaFsgjsqqTGXP5bxm/FV07VvLTs1X+eeGP9BCBrcB/16tg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723126178; c=relaxed/simple; bh=zbW+TnT2zxyMB+yxd0fACCt1cAOudRQVOD0lCGX/HEo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eqIf67oysaDwi0kAM7QDkPx7rvtQuTCFIG6V36ucq/iE4XVxul5Zc3ZMczObKItYBJ2BbHIpBDuMk8JRTm4Vqn5tg12z+ZK0jVi3UroZXBJDG8byizytivS3aJs2McUIjCSpWciEabdApimCwhGND7SlkidNyXCophLDXgwO414= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net; spf=pass smtp.mailfrom=digikod.net; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b=QqhTjXFW; arc=none smtp.client-ip=84.16.66.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=digikod.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b="QqhTjXFW" Received: from smtp-4-0000.mail.infomaniak.ch (smtp-4-0000.mail.infomaniak.ch [10.7.10.107]) by smtp-3-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4Wfpng0q8YzRVT; Thu, 8 Aug 2024 16:09:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1723126167; bh=MbLKs2A5zMNmmzak6XvmEHCMnOoCd8Xu8lOUJ5M2KQY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QqhTjXFW5BJKsWENy5GGCaj2cL+YpbF2ZFQOTgDmHVVg+Y+IOItc7XD/Xuz8gC1HI evfGSiybrDBagWMU9EKiHSHPNzU73aIMEjLAGVY0gWKCU1I6O6Ww8fZUxS4J9pZ5fI 3f0CYWuKs/sULKTbnDSDd4lFOqrOXVT1RApX4ego= Received: from unknown by smtp-4-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4Wfpnd5BQYzrQF; Thu, 8 Aug 2024 16:09:25 +0200 (CEST) Date: Thu, 8 Aug 2024 16:09:20 +0200 From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= To: Jann Horn Cc: Tahera Fahimi , outreachy@lists.linux.dev, gnoack@google.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, bjorn3_gh@protonmail.com, netdev@vger.kernel.org Subject: Re: [PATCH v2 1/4] Landlock: Add signal control Message-ID: <20240808.kaiyaeZoo1ha@digikod.net> References: <49557e48c1904d2966b8aa563215d2e1733dad95.1722966592.git.fahimitahera@gmail.com> <20240807.Yee4al2lahCo@digikod.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Infomaniak-Routing: alpha On Thu, Aug 08, 2024 at 03:10:54AM +0200, Jann Horn wrote: > On Thu, Aug 8, 2024 at 1:36 AM Tahera Fahimi wrote: > > On Wed, Aug 07, 2024 at 08:16:47PM +0200, Mickaël Salaün wrote: > > > On Tue, Aug 06, 2024 at 11:55:27PM +0200, Jann Horn wrote: > > > > On Tue, Aug 6, 2024 at 8:56 PM Jann Horn wrote: > > > > > On Tue, Aug 6, 2024 at 8:11 PM Tahera Fahimi wrote: > > > > > > Currently, a sandbox process is not restricted to send a signal > > > > > > (e.g. SIGKILL) to a process outside of the sandbox environment. > > > > > > Ability to sending a signal for a sandboxed process should be > > > > > > scoped the same way abstract unix sockets are scoped. Therefore, > > > > > > we extend "scoped" field in a ruleset with > > > > > > "LANDLOCK_SCOPED_SIGNAL" to specify that a ruleset will deny > > > > > > sending any signal from within a sandbox process to its > > > > > > parent(i.e. any parent sandbox or non-sandboxed procsses). > > > > [...] > > > > > > + if (is_scoped) > > > > > > + return 0; > > > > > > + > > > > > > + return -EPERM; > > > > > > +} > > > > > > + > > > > > > +static int hook_file_send_sigiotask(struct task_struct *tsk, > > > > > > + struct fown_struct *fown, int signum) > > > > > > I was wondering if we should handle this case, but I guess it makes > > > sense to have a consistent policy for all kind of user-triggerable > > > signals. > > > > > > > > > +{ > > > > > > + bool is_scoped; > > > > > > + const struct landlock_ruleset *dom, *target_dom; > > > > > > + struct task_struct *result = get_pid_task(fown->pid, fown->pid_type); > > > > > > > > > > I'm not an expert on how the fowner stuff works, but I think this will > > > > > probably give you "result = NULL" if the file owner PID has already > > > > > exited, and then the following landlock_get_task_domain() would > > > > > probably crash? But I'm not entirely sure about how this works. > > > > > > > > > > I think the intended way to use this hook would be to instead use the > > > > > "file_set_fowner" hook to record the owning domain (though the setup > > > > > for that is going to be kind of a pain...), see the Smack and SELinux > > > > > definitions of that hook. Or alternatively maybe it would be even > > > > > nicer to change the fown_struct to record a cred* instead of a uid and > > > > > euid and then use the domain from those credentials for this hook... > > > > > I'm not sure which of those would be easier. > > > > > > > > (For what it's worth, I think the first option would probably be > > > > easier to implement and ship for now, since you can basically copy > > > > what Smack and SELinux are already doing in their implementations of > > > > these hooks. I think the second option would theoretically result in > > > > nicer code, but it might require a bit more work, and you'd have to > > > > include the maintainers of the file locking code in the review of such > > > > refactoring and have them approve those changes. So if you want to get > > > > this patchset into the kernel quickly, the first option might be > > > > better for now?) > > > > > > > > > > I agree, let's extend landlock_file_security with a new "fown" pointer > > > to a Landlock domain. We'll need to call landlock_get_ruleset() in > > > hook_file_send_sigiotask(), and landlock_put_ruleset() in a new > > > hook_file_free_security(). > > I think we should add a new hook (hook_file_set_owner()) to initialize > > the "fown" pointer and call landlock_get_ruleset() in that? > > Yeah. Initialize the pointer in the file_set_fowner hook, and read the > pointer in the file_send_sigiotask hook. > > Note that in the file_set_fowner hook, you'll probably need to use > both landlock_get_ruleset() (to take a reference on the ruleset you're > storing in the fown pointer) and landlock_put_ruleset() (to drop the > reference to the ruleset that the fown pointer was pointing to > before). And you'll need to use some kind of lock to protect the fown > pointer - either by adding an appropriate lock next to your fown > pointer or by using some appropriate existing lock in "struct file". > Probably it's cleanest to have your own lock for this? (This lock will > have to be something like a spinlock, not a mutex, since you need to > be able to acquire it in the file_set_fowner hook, which runs inside > an RCU read-side critical section, where sleeping is forbidden - > acquiring a mutex can sleep and therefore is forbidden in this > context, acquiring a spinlock can't sleep.) Yes, I think this should work for file_set_fowner: struct landlock_ruleset *prev_dom, *new_dom; new_dom = landlock_get_current_domain(); landlock_get_ruleset(new_dom); /* Cf. f_modown() */ write_lock_irq(&filp->f_owner.lock); prev_dom = rcu_replace_pointer(&landlock_file(file)->fown_domain, new_dom, lockdep_is_held(&filp->f_owner.lock)); write_unlock_irq(&filp->f_owner.lock); landlock_put_ruleset_rcu(prev_dom); With landlock_put_ruleset_rcu() define with this: diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c index a93bdbf52fff..897116205520 100644 --- a/security/landlock/ruleset.c +++ b/security/landlock/ruleset.c @@ -524,6 +524,20 @@ void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset) } } +static void free_ruleset_rcu(struct rcu_head *const head) +{ + struct landlock_ruleset *ruleset; + + ruleset = container_of(head, struct landlock_ruleset, rcu); + free_ruleset(ruleset); +} + +void landlock_put_ruleset_rcu(struct landlock_ruleset *const ruleset) +{ + if (ruleset && refcount_dec_and_test(&ruleset->usage)) + call_rcu(&ruleset->rcu, free_ruleset_rcu); +} + /** * landlock_merge_ruleset - Merge a ruleset with a domain * diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h index c749fa0b3ecd..c930b39174b0 100644 --- a/security/landlock/ruleset.h +++ b/security/landlock/ruleset.h @@ -190,19 +190,35 @@ struct landlock_ruleset { * @work_free: Enables to free a ruleset within a lockless * section. This is only used by * landlock_put_ruleset_deferred() when @usage reaches zero. - * The fields @lock, @usage, @num_rules, @num_layers and + * The fields @rcu, @lock, @usage, @num_rules, @num_layers and * @access_masks are then unused. */ struct work_struct work_free; struct { - /** - * @lock: Protects against concurrent modifications of - * @root, if @usage is greater than zero. - */ - struct mutex lock; + union { + /** + * @rcu: Protects RCU read-side critical + * sections. This is only used by + * landlock_put_ruleset_rcu() when @usage + * reaches zero. + * + * Only used for domains. + */ + struct rcu_head rcu; + /** + * @lock: Protects against concurrent + * modifications of @root_inode and + * @root_net_port, if @usage is greater than + * zero. + * + * Only used for rulesets. + */ + struct mutex lock; + }; /** * @usage: Number of processes (i.e. domains) or file - * descriptors referencing this ruleset. + * descriptors referencing this ruleset. It can be + * zero in RCU read-side critical sections. */ refcount_t usage; /** @@ -241,6 +257,7 @@ landlock_create_ruleset(const access_mask_t access_mask_fs, void landlock_put_ruleset(struct landlock_ruleset *const ruleset); void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset); +void landlock_put_ruleset_rcu(struct landlock_ruleset *const ruleset); int landlock_insert_rule(struct landlock_ruleset *const ruleset, const struct landlock_id id,