linux-kernel - Re: [PATCH v4 2/5] security: Rewrite security_old_inode_init

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Message-ID: <3dc4f389ead98972cb7d09ef285a0065decb0ad0.camel@linux.ibm.com>
Date:   Thu, 17 Nov 2022 08:03:23 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>,
        dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org, casey@...aufler-ca.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, nicolas.bouchinet@...p-os.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        ocfs2-devel@....oracle.com
Subject: Re: [PATCH v4 2/5] security: Rewrite
 security_old_inode_init_security()

Hi Roberto,

On Thu, 2022-11-10 at 10:46 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
> 
> Rewrite security_old_inode_init_security() to call
> security_inode_init_security() before making changes to support multiple
> LSMs providing xattrs. Do it so that the required changes are done only in
> one place.

Only security_inode_init_security() has support for EVM.   Making
security_old_inode_init_security() a wrapper for
security_inode_init_security() could result in security.evm extended
attributes being created that previously weren't created.

In fact ocfs2 defines ocfs2_init_security_get() as a wrapper for both
the old and new inode_init_security calls based on the caller's
preference.   Only mknod and symlink seem to use the old function. 
Wondering why do they differentiate between callers?  (Cc'ing the ocfs2
mailing list as they're affected by this change.)

"[PATCH v4 1/5] reiserfs: Add missing calls to
reiserfs_security_free()"  fixed a memory leak.  I couldn't tell if
there was a similar memory leak in ocfs2, the only other user of
security_old_inode_init_security().

As ocfs2 already defines initxattrs, that leaves only reiserfs missing
initxattrs().  A better, cleaner solution would be to define one.

thanks,

Mimi

> 
> Define the security_initxattrs() callback and pass it to
> security_inode_init_security() as argument, to obtain the first xattr
> provided by LSMs.
> 
> This behavior is a bit different from the current one. Before this patch
> calling call_int_hook() could cause multiple LSMs to provide an xattr,
> since call_int_hook() does not stop when an LSM returns zero. The caller of
> security_old_inode_init_security() receives the last xattr set. The pointer
> of the xattr value of previous LSMs is lost, causing memory leaks.
> 
> However, in practice, this scenario does not happen as the only in-tree
> LSMs providing an xattr at inode creation time are SELinux and Smack, which
> are mutually exclusive.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>b