From: Jarkko Sakkinen <jarkko@kernel.org>
To: Stefan Berger <stefanb@linux.ibm.com>
Cc: linux-integrity@vger.kernel.org, zohar@linux.ibm.com,
serge@hallyn.com, brauner@kernel.org, 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>
Subject: Re: [PATCH v15 01/26] securityfs: rework dentry creation
Date: Fri, 10 Feb 2023 02:39:19 +0200 [thread overview]
Message-ID: <Y+WSDX/zxRpxzqLP@kernel.org> (raw)
In-Reply-To: <20230206140253.3755945-2-stefanb@linux.ibm.com>
On Mon, Feb 06, 2023 at 09:02:28AM -0500, 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
nit: "Constrating this with debugfs"
Passive form is better when there is no well-defined definition of "we".
> 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
> securityfs_create_dentry() until it is removed. Since it is virtually
> guaranteed that there is at least one user of securityfs that has created
> dentries the initial securityfs mount cannot go away until all dentries
> have been removed.
>
> Since most of the users of the initial securityfs mount don't go away
> until the system is shutdown the initial securityfs won't go away when
> unmounted. Instead a mount will usually surface the same superblock as
> before. The additional dget() doesn't matter in this scenario since it
> is required that all dentries have been cleaned up by the respective
> users before the superblock can be destroyed, i.e. superblock shutdown
> is tied to the lifetime of the associated dentries.
>
> However, in order to support ima namespaces we need to extend securityfs
> to support being mounted outside of the initial user namespace. For
> namespaced users the pinning logic doesn't make sense. Whereas in the
> initial namespace the securityfs instance and the associated data
> structures of its users can't go away for reason explained earlier users
> of non-initial securityfs instances do go away when the last users of
> the namespace are gone.
"for reason explained earlier" ?
> So for those users we neither want to duplicate the pinning logic nor
> make the global securityfs instance display different information based
> on the namespace. Both options would be really messy and hacky.
>
> Instead we will simply give each namespace its own securityfs instance
> similar to how each ipc namespace has its own mqueue instance and all
> entries in there are cleaned up on umount or when the last user of the
> associated namespace is gone.
>
> This means that the superblock's lifetime isn't tied to the dentries.
> Instead the last umount, without any fds kept open, will trigger a clean
> shutdown. But now the additional dget() gets in the way. Instead of
> being able to rely on the generic superblock shutdown logic we would
> need to drop the additional dentry reference during superblock shutdown
> for all associated users. That would force the use of a generic
> coordination mechanism for current and future users of securityfs which
> is unnecessary. Simply remove the additional dget() in
> securityfs_dentry_create().
>
> In securityfs_remove() we will call dget() to take an additional
> reference on the dentry about to be removed. After simple_unlink() or
> simple_rmdir() have dropped the dentry refcount we can call d_delete()
> which will either turn the dentry into negative dentry if our earlier
> dget() is the only reference to the dentry, i.e. it has no other users,
> or remove it from the hashqueues in case there are additional users.
>
> All of these changes should not have any effect on the userspace
> semantics of the initial securityfs mount.
>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> Cc: John Johansen <john.johansen@canonical.com>
> Cc: Matthew Garrett <mjg59@srcf.ucam.org>
> Cc: Micah Morton <mortonm@chromium.org>
> Cc: Kentaro Takeda <takedakn@nttdata.co.jp>
> Cc: James Morris <jmorris@namei.org>
> Cc: Jarkko Sakkinen <jarkko@kernel.org>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
>
> ---
> v13:
> - Slight improvements in 1st paragraph of commit message
> ---
> security/inode.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/security/inode.c b/security/inode.c
> index 6c326939750d..13e6780c4444 100644
> --- a/security/inode.c
> +++ b/security/inode.c
> @@ -159,7 +159,6 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
> inode->i_fop = fops;
> }
> d_instantiate(dentry, inode);
> - dget(dentry);
> inode_unlock(dir);
> return dentry;
>
> @@ -302,10 +301,12 @@ void securityfs_remove(struct dentry *dentry)
> dir = d_inode(dentry->d_parent);
> inode_lock(dir);
> if (simple_positive(dentry)) {
> + dget(dentry);
> if (d_is_dir(dentry))
> simple_rmdir(dir, dentry);
> else
> simple_unlink(dir, dentry);
> + d_delete(dentry);
> dput(dentry);
> }
> inode_unlock(dir);
> --
> 2.37.3
>
BR, Jarkko
next prev parent reply other threads:[~2023-02-10 0:39 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-06 14:02 [PATCH v15 00/26] ima: Namespace IMA with audit support in IMA-ns Stefan Berger
2023-02-06 14:02 ` [PATCH v15 01/26] securityfs: rework dentry creation Stefan Berger
2023-02-10 0:39 ` Jarkko Sakkinen [this message]
2023-02-06 14:02 ` [PATCH v15 02/26] securityfs: Extend securityfs with namespacing support Stefan Berger
2023-02-06 14:02 ` [PATCH v15 03/26] ima: Define ima_namespace struct and start moving variables into it Stefan Berger
2023-02-06 14:02 ` [PATCH v15 04/26] ima: Move arch_policy_entry into ima_namespace Stefan Berger
2023-02-06 14:02 ` [PATCH v15 05/26] ima: Move ima_htable " Stefan Berger
2023-02-06 14:02 ` [PATCH v15 06/26] ima: Move measurement list related variables " Stefan Berger
2023-02-06 14:02 ` [PATCH v15 07/26] ima: Move some IMA policy and filesystem " Stefan Berger
2023-02-06 14:02 ` [PATCH v15 08/26] ima: Move IMA securityfs files into ima_namespace or onto stack Stefan Berger
2023-02-06 14:02 ` [PATCH v15 09/26] ima: Move ima_lsm_policy_notifier into ima_namespace Stefan Berger
2023-02-06 14:02 ` [PATCH v15 10/26] ima: Switch to lazy lsm policy updates for better performance Stefan Berger
2023-02-06 14:02 ` [PATCH v15 11/26] ima: Define mac_admin_ns_capable() as a wrapper for ns_capable() Stefan Berger
2023-02-06 14:02 ` [PATCH v15 12/26] ima: Only accept AUDIT rules for non-init_ima_ns namespaces for now Stefan Berger
2023-02-06 14:02 ` [PATCH v15 13/26] userns: Add pointer to ima_namespace to user_namespace Stefan Berger
2023-02-06 14:02 ` [PATCH v15 14/26] ima: Implement hierarchical processing of file accesses Stefan Berger
2023-02-06 14:02 ` [PATCH v15 15/26] ima: Implement ima_free_policy_rules() for freeing of an ima_namespace Stefan Berger
2023-02-06 14:02 ` [PATCH v15 16/26] ima: Add functions for creating and " Stefan Berger
2023-02-06 14:02 ` [PATCH v15 17/26] integrity/ima: Define ns_status for storing namespaced iint data Stefan Berger
2023-02-06 14:02 ` [PATCH v15 18/26] integrity: Add optional callback function to integrity_inode_free() Stefan Berger
2023-02-06 14:02 ` [PATCH v15 19/26] ima: Namespace audit status flags Stefan Berger
2023-02-06 14:02 ` [PATCH v15 20/26] ima: Remove unused iints from the integrity_iint_cache Stefan Berger
2023-02-06 14:02 ` [PATCH v15 21/26] ima: Setup securityfs for IMA namespace Stefan Berger
2023-02-06 14:02 ` [PATCH v15 22/26] ima: Introduce securityfs file to activate an " Stefan Berger
2023-02-06 14:02 ` [PATCH v15 23/26] ima: Show owning user namespace's uid and gid when displaying policy Stefan Berger
2023-02-06 14:02 ` [PATCH v15 24/26] ima: Limit number of policy rules in non-init_ima_ns Stefan Berger
2023-02-06 14:02 ` [PATCH v15 25/26] ima: Restrict informational audit messages to init_ima_ns Stefan Berger
2023-02-06 14:02 ` [PATCH v15 26/26] ima: Enable IMA namespaces Stefan Berger
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