linux-kernel - Re: [PATCH v2 3/7] ima: Ensure lock is held when setting iint pointer in inode security blob

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Message-ID: <85823922-0947-488e-ba95-f6c0e3132313@huaweicloud.com>
Date: Wed, 15 Jan 2025 11:51:22 +0100
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: Mimi Zohar <zohar@...ux.ibm.com>, viro@...iv.linux.org.uk,
 brauner@...nel.org, jack@...e.cz, dmitry.kasatkin@...il.com,
 eric.snowberg@...cle.com, paul@...l-moore.com, jmorris@...ei.org,
 serge@...lyn.com
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
 Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v2 3/7] ima: Ensure lock is held when setting iint pointer
 in inode security blob

On 1/14/2025 3:20 PM, Mimi Zohar wrote:
> On Thu, 2024-11-28 at 11:06 +0100, Roberto Sassu wrote:
>> From: Roberto Sassu <roberto.sassu@...wei.com>
>>
>> IMA stores a pointer of the ima_iint_cache structure, containing integrity
>> metadata, in the inode security blob. However, check and assignment of this
>> pointer is not atomic, and it might happen that two tasks both see that the
>> iint pointer is NULL and try to set it, causing a memory leak.
>>
>> Ensure that the iint check and assignment is guarded, by adding a lockdep
>> assertion in ima_inode_get().
> 
> -> is guarded by the ima_iint_cache_lock mutex, ...

By the iint_lock mutex...

>> Consequently, guard the remaining ima_inode_get() calls, in
>> ima_post_create_tmpfile() and ima_post_path_mknod(), to avoid the lockdep
>> warnings.
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>> ---
>>   security/integrity/ima/ima_iint.c |  2 ++
>>   security/integrity/ima/ima_main.c | 14 ++++++++++++--
>>   2 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
>> index dcc32483d29f..fca9db293c79 100644
>> --- a/security/integrity/ima/ima_iint.c
>> +++ b/security/integrity/ima/ima_iint.c
>> @@ -97,6 +97,8 @@ struct ima_iint_cache *ima_inode_get(struct inode *inode)
>>   	if (!iint_lock)
>>   		return NULL;
>>   
>> +	lockdep_assert_held(&iint_lock->mutex);
>> +
> 
> lockdep_assert_held() doesn't actually "ensure" the lock is held, but emits a warning
> when the lock is not held (if debugging is enabled).  Semantically "ensure" gives the
> impression of enforcing.

I agree. I would replace ensure with detect.

Thanks

Roberto

> Mimi
> 
>>   	iint = iint_lock->iint;
>>   	if (iint)
>>   		return iint;
>> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
>> index 05cfb04cd02b..1e474ff6a777 100644
>> --- a/security/integrity/ima/ima_main.c
>> +++ b/security/integrity/ima/ima_main.c
>> @@ -705,14 +705,19 @@ static void ima_post_create_tmpfile(struct mnt_idmap *idmap,
>>   	if (!must_appraise)
>>   		return;
>>   
>> +	ima_iint_lock(inode);
>> +
>>   	/* Nothing to do if we can't allocate memory */
>>   	iint = ima_inode_get(inode);
>> -	if (!iint)
>> +	if (!iint) {
>> +		ima_iint_unlock(inode);
>>   		return;
>> +	}
>>   
>>   	/* needed for writing the security xattrs */
>>   	set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
>>   	iint->ima_file_status = INTEGRITY_PASS;
>> +	ima_iint_unlock(inode);
>>   }
>>   
>>   /**
>> @@ -737,13 +742,18 @@ static void ima_post_path_mknod(struct mnt_idmap *idmap,
>> struct dentry *dentry)
>>   	if (!must_appraise)
>>   		return;
>>   
>> +	ima_iint_lock(inode);
>> +
>>   	/* Nothing to do if we can't allocate memory */
>>   	iint = ima_inode_get(inode);
>> -	if (!iint)
>> +	if (!iint) {
>> +		ima_iint_unlock(inode);
>>   		return;
>> +	}
>>   
>>   	/* needed for re-opening empty files */
>>   	iint->flags |= IMA_NEW_FILE;
>> +	ima_iint_unlock(inode);
>>   }
>>   
>>   /**
>