From: "Serge E. Hallyn" <serge@hallyn.com>
To: Christian Brauner <brauner@kernel.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
Stefan Berger <stefanb@linux.ibm.com>,
linux-integrity@vger.kernel.org, zohar@linux.ibm.com,
christian.brauner@ubuntu.com, containers@lists.linux.dev,
dmitry.kasatkin@gmail.com, ebiederm@xmission.com,
krzysztof.struczynski@huawei.com, roberto.sassu@huawei.com,
mpeters@redhat.com, lhinds@redhat.com, lsturman@redhat.com,
puiterwi@redhat.com, jejb@linux.ibm.com, jamjoom@us.ibm.com,
linux-kernel@vger.kernel.org, paul@paul-moore.com,
rgb@redhat.com, linux-security-module@vger.kernel.org,
jmorris@namei.org, jpenumak@redhat.com,
John Johansen <john.johansen@canonical.com>,
Matthew Garrett <mjg59@srcf.ucam.org>,
Micah Morton <mortonm@chromium.org>,
Kentaro Takeda <takedakn@nttdata.co.jp>,
Jarkko Sakkinen <jarkko@kernel.org>
Subject: Re: [PATCH v12 01/26] securityfs: rework dentry creation
Date: Tue, 10 May 2022 15:41:51 -0500 [thread overview]
Message-ID: <20220510204151.GA12935@mail.hallyn.com> (raw)
In-Reply-To: <20220510155107.srxifzuqfstvet2f@wittgenstein>
On Tue, May 10, 2022 at 05:51:07PM +0200, Christian Brauner wrote:
> On Tue, May 10, 2022 at 09:10:25AM -0500, Serge Hallyn wrote:
> > On Tue, May 10, 2022 at 12:25:25PM +0200, Christian Brauner wrote:
> > > On Mon, May 09, 2022 at 02:54:14PM -0500, Serge Hallyn wrote:
> > > > On Wed, Apr 20, 2022 at 10:06:08AM -0400, Stefan Berger wrote:
> > > > > From: Christian Brauner <brauner@kernel.org>
> > > > >
> > > > > When securityfs creates a new file or directory via
> > > > > securityfs_create_dentry() it will take an additional reference on the
> > > > > newly created dentry after it has attached the new inode to the new
> > > > > dentry and added it to the hashqueues.
> > > > > If we contrast this with debugfs which has the same underlying logic as
> > > > > securityfs. It uses a similar pairing as securityfs. Where securityfs
> > > > > has the securityfs_create_dentry() and securityfs_remove() pairing,
> > > > > debugfs has the __debugfs_create_file() and debugfs_remove() pairing.
> > > > >
> > > > > In contrast to securityfs, debugfs doesn't take an additional reference
> > > > > on the newly created dentry in __debugfs_create_file() which would need
> > > > > to be put in debugfs_remove().
> > > > >
> > > > > The additional dget() isn't a problem per se. In the current
> > > > > implementation of securityfs each created dentry pins the filesystem via
> > > >
> > > > Is 'via' an extra word here or is there a missing word?
> > > >
> > > > I'll delay the rest of my response as the missing word may answer my
> > > > remaining question :)
> > >
> > > It can be both. It should either be removed or it should be followed by
> > > "securityfs_create_dentry()". securityfs_create_dentry() takes two
> > > references one in lookup_one_len() and another one explicitly via
> > > dget(). The latter one isn't needed. Some of that has been covered in an
> > > earlier thread:
> > > https://lore.kernel.org/lkml/20220105101815.ldsm4s5yx7pmuiil@wittgenstein
> >
> > Yes, I saw that two references were being taken. And near as I can tell,
> > the second one was never being dropped. So if you tell me that before this
> > patch the dentries are never freed, then I'm happy. Otherwise, I'm
> > bothered the fact that no matching dput is being deleted in the code (to
> > match the extra dget being removed). So where is the code where the final
> > dput was happening, and is it the d_delete() you're adding which is making
> > it so that that dput won't be called now?
>
> * So consider mounting securityfs _without this patch applied_:
>
> mount -t securityfs /sfs
>
> and assume we only have a single user that creates a file "foo" via
>
> securityfs_create_file()
> {
> lookup_one_len(); // first dget()
> dget(); // second dget()
> }
>
> now assume that user at some point calls
>
> void securityfs_remove()
> {
> if (d_is_dir(dentry))
> simple_rmdir(dir, dentry); // first dput()
> else
> simple_unlink(dir, dentry); // first dput()
> dput(dentry); // second dput()
> }
>
> * Now consider mounting securityfs _with this patch applied_:
>
> securityfs_create_file()
> {
> lookup_one_len(); // first dget()
> }
>
> void securityfs_remove()
> {
> dget(); // second dget()
> if (d_is_dir(dentry))
> simple_rmdir(dir, dentry); // first dput()
> else
> simple_unlink(dir, dentry); // first dput()
> dput(dentry); // second dput()
> }
Thanks, I get it now
Reviewed-by: Serge Hallyn <serge@hallyn.com>
next prev parent reply other threads:[~2022-05-10 20:42 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-20 14:06 [PATCH v12 00/26] ima: Namespace IMA with audit support in IMA-ns Stefan Berger
2022-04-20 14:06 ` [PATCH v12 01/26] securityfs: rework dentry creation Stefan Berger
2022-05-09 19:54 ` Serge E. Hallyn
2022-05-09 20:36 ` Serge E. Hallyn
2022-05-10 8:43 ` Amir Goldstein
2022-05-10 10:38 ` Christian Brauner
2022-05-10 14:51 ` Serge E. Hallyn
2022-05-10 14:53 ` Serge E. Hallyn
2022-05-10 10:26 ` Christian Brauner
2022-05-10 10:25 ` Christian Brauner
2022-05-10 14:10 ` Serge E. Hallyn
2022-05-10 15:51 ` Christian Brauner
2022-05-10 18:51 ` Serge E. Hallyn
2022-05-10 20:41 ` Serge E. Hallyn [this message]
2022-06-09 14:27 ` Mimi Zohar
2022-05-10 16:50 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 02/26] securityfs: Extend securityfs with namespacing support Stefan Berger
2022-05-21 2:23 ` Serge E. Hallyn
2022-05-21 9:38 ` Christian Brauner
2022-05-21 15:09 ` Serge E. Hallyn
2022-07-07 14:34 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 03/26] ima: Define ima_namespace struct and start moving variables into it Stefan Berger
2022-05-21 2:33 ` Serge E. Hallyn
2022-05-24 14:57 ` Stefan Berger
2022-05-24 15:05 ` Serge E. Hallyn
2022-05-24 16:18 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 04/26] ima: Move arch_policy_entry into ima_namespace Stefan Berger
2022-05-21 2:46 ` Serge E. Hallyn
2022-05-21 3:07 ` Serge E. Hallyn
2022-07-07 14:12 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 05/26] ima: Move ima_htable " Stefan Berger
2022-05-21 2:50 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 06/26] ima: Move measurement list related variables " Stefan Berger
2022-05-21 2:55 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 07/26] ima: Move some IMA policy and filesystem " Stefan Berger
2022-05-21 3:03 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 08/26] ima: Move IMA securityfs files into ima_namespace or onto stack Stefan Berger
2022-05-21 3:24 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 09/26] ima: Move ima_lsm_policy_notifier into ima_namespace Stefan Berger
2022-05-22 2:35 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 10/26] ima: Switch to lazy lsm policy updates for better performance Stefan Berger
2022-05-22 17:06 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 11/26] ima: Define mac_admin_ns_capable() as a wrapper for ns_capable() Stefan Berger
2022-05-22 17:31 ` Serge E. Hallyn
2022-05-24 14:17 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 12/26] ima: Only accept AUDIT rules for non-init_ima_ns namespaces for now Stefan Berger
2022-05-22 17:38 ` Serge E. Hallyn
2022-05-24 13:25 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 13/26] userns: Add pointer to ima_namespace to user_namespace Stefan Berger
2022-05-22 18:24 ` Serge E. Hallyn
2022-05-23 9:59 ` Christian Brauner
2022-05-23 11:31 ` Stefan Berger
2022-05-23 12:41 ` Christian Brauner
2022-05-23 12:58 ` Stefan Berger
2022-05-23 14:25 ` Serge E. Hallyn
2022-07-07 14:14 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 14/26] ima: Implement hierarchical processing of file accesses Stefan Berger
2022-05-23 0:42 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 15/26] ima: Implement ima_free_policy_rules() for freeing of an ima_namespace Stefan Berger
2022-05-23 0:43 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 16/26] ima: Add functions for creating and " Stefan Berger
2022-05-30 1:07 ` Serge E. Hallyn
2022-04-20 14:06 ` [PATCH v12 17/26] integrity/ima: Define ns_status for storing namespaced iint data Stefan Berger
2022-04-20 14:06 ` [PATCH v12 18/26] integrity: Add optional callback function to integrity_inode_free() Stefan Berger
2022-04-20 14:06 ` [PATCH v12 19/26] ima: Namespace audit status flags Stefan Berger
2022-04-20 14:06 ` [PATCH v12 20/26] ima: Remove unused iints from the integrity_iint_cache Stefan Berger
2022-04-20 14:06 ` [PATCH v12 21/26] ima: Setup securityfs for IMA namespace Stefan Berger
2022-05-30 1:16 ` Serge E. Hallyn
2022-05-31 19:26 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 22/26] ima: Introduce securityfs file to activate an " Stefan Berger
2022-04-20 14:06 ` [PATCH v12 23/26] ima: Show owning user namespace's uid and gid when displaying policy Stefan Berger
2022-05-22 17:54 ` Serge E. Hallyn
2022-05-24 13:19 ` Stefan Berger
2022-04-20 14:06 ` [PATCH v12 24/26] ima: Limit number of policy rules in non-init_ima_ns Stefan Berger
2022-04-20 14:06 ` [PATCH v12 25/26] ima: Restrict informational audit messages to init_ima_ns Stefan Berger
2022-04-20 14:06 ` [PATCH v12 26/26] ima: Enable IMA namespaces Stefan Berger
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