linux-kernel - Re: [RFC PATCH 2/2] integrity: double check iint

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Message-ID: <1a2245c6-3cab-7085-83d3-55b083619303@i-love.sakura.ne.jp>
Date:   Tue, 23 Mar 2021 10:46:52 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers@...nel.org>
Subject: Re: [RFC PATCH 2/2] integrity: double check iint_cache was
 initialized

On 2021/03/20 5:03, Mimi Zohar wrote:
> The integrity's "iint_cache" is initialized at security_init().  Only
> after an IMA policy is loaded, which is initialized at late_initcall,
> is a file's integrity status stored in the "iint_cache".
> 
> All integrity_inode_get() callers first verify that the IMA policy has
> been loaded, before calling it.  Yet for some reason, it is still being
> called, causing a NULL pointer dereference.
> 
> qemu-system-x86_64 (...snipped...) lsm=smack (...snipped...)

Hmm, why are you using lsm=smack instead of security=smack ?
Since use of lsm= overrides CONFIG_LSM="lockdown,yama,safesetid,integrity,tomoyo,smack,bpf" settings,
only smack is activated, which means that integrity_iintcache_init() will not be called by

  DEFINE_LSM(integrity) = {
  	.name = "integrity",
  	.init = integrity_iintcache_init,
  };

declaration. That's the reason iint_cache == NULL when integrity_inode_get() is called.