linux-kernel - Re: [syzbot] [lsm?] general protection fault in hook_inode_free

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Message-ID: <eb168f2f-948b-4a3b-9237-92902f0c7438@I-love.SAKURA.ne.jp>
Date: Thu, 11 Jul 2024 09:30:40 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Paul Moore <paul@...l-moore.com>,
        Mickaël Salaün
 <mic@...ikod.net>
Cc: Jann Horn <jannh@...gle.com>, Christian Brauner <brauner@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Kees Cook <keescook@...omium.org>,
        syzbot <syzbot+5446fbf332b0602ede0b@...kaller.appspotmail.com>,
        jmorris@...ei.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, serge@...lyn.com,
        syzkaller-bugs@...glegroups.com, linux-fsdevel@...r.kernel.org
Subject: Re: [syzbot] [lsm?] general protection fault in
 hook_inode_free_security

On 2024/06/28 3:28, Paul Moore wrote:
> It's also worth mentioning that while we always allocate i_security in
> security_inode_alloc() right now, I can see a world where we allocate
> the i_security field based on need using the lsm_blob_size info (maybe
> that works today?  not sure how kmem_cache handled 0 length blobs?).
> The result is that there might be a legitimate case where i_security
> is NULL, yet we still want to call into the LSM using the
> inode_free_security() implementation hook.

As a LKM-based LSM user, I don't like dependency on the lsm_blob_size info.

Since LKM-based LSM users cannot use lsm_blob_size due to __ro_after_init,
LKM-based LSM users depend on individual LSM hooks being called even if
i_security is NULL. How do we provide hooks for AV/EDR which cannot be 
built into vmlinux (due to distributor's support policy) ? They cannot be
benefited from infrastructure-managed security blobs.