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

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Message-ID: <8a8763a7-eeeb-3578-d50c-c15919fbe1f9@i-love.sakura.ne.jp>
Date:   Tue, 23 Mar 2021 23:01:31 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.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 2021/03/23 22:37, Tetsuo Handa wrote:
> On 2021/03/23 21:09, Mimi Zohar wrote:
>> Please take a look at the newer version of this patch.   Do you want to
>> add any tags?
> 
> Oh, I didn't know that you already posted the newer version.
> 
>> diff --git a/security/integrity/iint.c b/security/integrity/iint.c
>> index 1d20003243c3..0ba01847e836 100644
>> --- a/security/integrity/iint.c
>> +++ b/security/integrity/iint.c
>> @@ -98,6 +98,14 @@ struct integrity_iint_cache *integrity_inode_get(struct inode *inode)
>>  	struct rb_node *node, *parent = NULL;
>>  	struct integrity_iint_cache *iint, *test_iint;
>>  
>> +	/*
>> +	 * The integrity's "iint_cache" is initialized at security_init(),
>> +	 * unless it is not included in the ordered list of LSMs enabled
>> +	 * on the boot command line.
>> +	 */
>> +	if (!iint_cache)
>> +		panic("%s: lsm=integrity required.\n", __func__);
>> +
> 
> This looks strange. If "lsm=" parameter must include "integrity",
> it implies that nobody is allowed to disable "integrity" at boot.
> Then, why not unconditionally call integrity_iintcache_init() by
> not counting on DEFINE_LSM(integrity) declaration?

Or, I think below one is also possible.

diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index 1d20003243c3..37afc5168891 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -19,6 +19,7 @@
 #include <linux/uaccess.h>
 #include <linux/security.h>
 #include <linux/lsm_hooks.h>
+#include <linux/sched/mm.h>
 #include "integrity.h"
 
 static struct rb_root integrity_iint_tree = RB_ROOT;
@@ -85,6 +86,20 @@ static void iint_free(struct integrity_iint_cache *iint)
 	kmem_cache_free(iint_cache, iint);
 }
 
+static void init_once(void *foo)
+{
+	struct integrity_iint_cache *iint = foo;
+
+	memset(iint, 0, sizeof(*iint));
+	iint->ima_file_status = INTEGRITY_UNKNOWN;
+	iint->ima_mmap_status = INTEGRITY_UNKNOWN;
+	iint->ima_bprm_status = INTEGRITY_UNKNOWN;
+	iint->ima_read_status = INTEGRITY_UNKNOWN;
+	iint->ima_creds_status = INTEGRITY_UNKNOWN;
+	iint->evm_status = INTEGRITY_UNKNOWN;
+	mutex_init(&iint->mutex);
+}
+
 /**
  * integrity_inode_get - find or allocate an iint associated with an inode
  * @inode: pointer to the inode
@@ -102,6 +117,18 @@ struct integrity_iint_cache *integrity_inode_get(struct inode *inode)
 	if (iint)
 		return iint;
 
+	if (!iint_cache) {
+		static DEFINE_MUTEX(lock);
+		unsigned int flags = memalloc_nofs_save();
+
+		mutex_lock(&lock);
+		if (!iint_cache)
+			iint_cache = kmem_cache_create("iint_cache",
+						       sizeof(struct integrity_iint_cache),
+						       0, SLAB_PANIC, init_once);
+		mutex_unlock(&lock);
+		memalloc_nofs_restore(flags);
+	}
 	iint = kmem_cache_alloc(iint_cache, GFP_NOFS);
 	if (!iint)
 		return NULL;
@@ -150,25 +177,8 @@ void integrity_inode_free(struct inode *inode)
 	iint_free(iint);
 }
 
-static void init_once(void *foo)
-{
-	struct integrity_iint_cache *iint = foo;
-
-	memset(iint, 0, sizeof(*iint));
-	iint->ima_file_status = INTEGRITY_UNKNOWN;
-	iint->ima_mmap_status = INTEGRITY_UNKNOWN;
-	iint->ima_bprm_status = INTEGRITY_UNKNOWN;
-	iint->ima_read_status = INTEGRITY_UNKNOWN;
-	iint->ima_creds_status = INTEGRITY_UNKNOWN;
-	iint->evm_status = INTEGRITY_UNKNOWN;
-	mutex_init(&iint->mutex);
-}
-
 static int __init integrity_iintcache_init(void)
 {
-	iint_cache =
-	    kmem_cache_create("iint_cache", sizeof(struct integrity_iint_cache),
-			      0, SLAB_PANIC, init_once);
 	return 0;
 }
 DEFINE_LSM(integrity) = {