From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huaweicloud.com>,
mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com,
dmitry.kasatkin@gmail.com, paul@paul-moore.com,
jmorris@namei.org, serge@hallyn.com,
stephen.smalley.work@gmail.com, eparis@parisplace.org,
casey@schaufler-ca.com
Cc: ocfs2-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
linux-kernel@vger.kernel.org, keescook@chromium.org,
nicolas.bouchinet@clip-os.org,
Roberto Sassu <roberto.sassu@huawei.com>
Subject: Re: [PATCH v7 4/6] security: Allow all LSMs to provide xattrs for inode_init_security hook
Date: Mon, 20 Feb 2023 07:43:24 -0500 [thread overview]
Message-ID: <22f48112c2fbc2812317c33af13accb022e9abdf.camel@linux.ibm.com> (raw)
In-Reply-To: <20221201104125.919483-5-roberto.sassu@huaweicloud.com>
On Thu, 2022-12-01 at 11:41 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> Currently, security_inode_init_security() supports only one LSM providing
> an xattr and EVM calculating the HMAC on that xattr, plus other inode
> metadata.
>
> Allow all LSMs to provide one or multiple xattrs, by extending the security
> blob reservation mechanism. Introduce the new lbs_xattr field of the
> lsm_blob_sizes structure, so that each LSM can specify how many xattrs it
> needs, and the LSM infrastructure knows how many xattr slots it should
> allocate.
>
> Dynamically allocate the xattrs array to be populated by LSMs with the
> inode_init_security hook, and pass it to the latter instead of the
> name/value/len triple. Update the documentation accordingly, and fix the
> description of the xattr name, as it is not allocated anymore.
>
> Since the LSM infrastructure, at initialization time, updates the number of
> the requested xattrs provided by each LSM with a corresponding offset in
> the security blob (in this case the xattr array), it makes straightforward
> for an LSM to access the right position in the xattr array.
>
> There is still the issue that an LSM might not fill the xattr, even if it
> requests it (legitimate case, for example it might have been loaded but not
> initialized with a policy). Since users of the xattr array (e.g. the
> initxattrs() callbacks) detect the end of the xattr array by checking if
> the xattr name is NULL, not filling an xattr would cause those users to
> stop scanning xattrs prematurely.
>
> Solve that issue by introducing security_check_compact_filled_xattrs(),
> which does a basic check of the xattr array (if the xattr name is filled,
> the xattr value should be too, and viceversa), and compacts the xattr array
> by removing the holes.
>
> An alternative solution would be to let users of the xattr array know the
> number of elements of that array, so that they don't have to check the
> termination. However, this seems more invasive, compared to a simple move
> of few array elements.
>
> security_check_compact_filled_xattrs() also determines how many xattrs in
> the xattr array have been filled. If there is none, skip
> evm_inode_init_security() and initxattrs(). Skipping the former also avoids
> EVM to crash the kernel, as it is expecting a filled xattr.
>
> Finally, adapt both SELinux and Smack to use the new definition of the
> inode_init_security hook, and to correctly fill the designated slots in the
> xattr array. For Smack, reserve space for the other defined xattrs although
> they are not set yet in smack_inode_init_security().
>
> Reported-by: Nicolas Bouchinet <nicolas.bouchinet@clip-os.org> (EVM crash)
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
next prev parent reply other threads:[~2023-02-20 12:44 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-01 10:41 [PATCH v7 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes Roberto Sassu
2022-12-01 10:41 ` [PATCH v7 1/6] reiserfs: Switch to security_inode_init_security() Roberto Sassu
2023-02-17 19:47 ` Mimi Zohar
2022-12-01 10:41 ` [PATCH v7 2/6] ocfs2: " Roberto Sassu
2023-01-10 8:55 ` Roberto Sassu
2023-01-12 17:21 ` Paul Moore
2023-02-08 14:33 ` Roberto Sassu
2023-02-09 21:05 ` Paul Moore
2023-02-21 6:45 ` Joseph Qi
2023-02-21 7:51 ` Roberto Sassu
2023-02-17 19:51 ` Mimi Zohar
2023-02-17 21:30 ` Mimi Zohar
2023-02-20 9:27 ` Roberto Sassu
2023-02-20 11:08 ` Mimi Zohar
2023-02-20 12:20 ` Roberto Sassu
2023-02-20 12:40 ` Mimi Zohar
2023-02-20 8:34 ` Roberto Sassu
2022-12-01 10:41 ` [PATCH v7 3/6] security: Remove security_old_inode_init_security() Roberto Sassu
2023-02-19 19:41 ` Mimi Zohar
2022-12-01 10:41 ` [PATCH v7 4/6] security: Allow all LSMs to provide xattrs for inode_init_security hook Roberto Sassu
2023-02-20 12:43 ` Mimi Zohar [this message]
2022-12-01 10:41 ` [PATCH v7 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure Roberto Sassu
2023-02-19 19:41 ` Mimi Zohar
2022-12-01 10:41 ` [PATCH v7 6/6] evm: Support multiple LSMs providing an xattr Roberto Sassu
2023-02-19 19:42 ` Mimi Zohar
2023-02-20 9:49 ` Roberto Sassu
2023-02-20 10:56 ` Mimi Zohar
2023-01-12 17:15 ` [PATCH v7 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes Paul Moore
2023-01-13 10:35 ` Roberto Sassu
2023-03-08 22:16 ` Paul Moore
2023-03-09 7:53 ` Roberto Sassu
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