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From: THOBY Simon <Simon.THOBY@viveris.fr>
To: Mimi Zohar <zohar@linux.ibm.com>,
	"dmitry.kasatkin@gmail.com" <dmitry.kasatkin@gmail.com>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	BARVAUX Didier <Didier.BARVAUX@viveris.fr>
Cc: Paul Moore <paul@paul-moore.com>
Subject: Re: [PATCH v4 2/5] IMA: block writes of the security.ima xattr with unsupported algorithms
Date: Wed, 28 Jul 2021 12:53:54 +0000	[thread overview]
Message-ID: <7bc627f3-a3bb-1cf4-44dc-097b241ac7ad@viveris.fr> (raw)
In-Reply-To: <3a576c8f562201f441a72bb7232c4bb0faa36318.camel@linux.ibm.com>

Hi Mimi,

On 7/28/21 2:43 PM, Mimi Zohar wrote:
> Hi Simon,
> 
> On Wed, 2021-07-28 at 07:00 +0000, THOBY Simon wrote: 
>>>> +
>>>> +	if (likely(dentry_hash == ima_hash_algo
>>>> +	    || crypto_has_alg(hash_algo_name[dentry_hash], 0, 0)))
>>>> +		return 0;
>>>> +
>>>> +	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
>>>> +	/* no memory available ? no file path for you */
>>>
>>> The comment here is unnecessary.  Avoid or limit comments inside a
>>> function.  Refer to the section "8) Commenting" in
>>> Documentation/process/coding-style.rst
>>>
>>>> +	if (pathbuf)
>>>> +		path = dentry_path(dentry, pathbuf, PATH_MAX);
>>>> +
>>>> +	/* disallow xattr writes with algorithms not built in the kernel */
>>>> +	integrity_audit_msg(AUDIT_INTEGRITY_DATA, d_inode(dentry),
>>>> +		path, "collect_data", "unavailable-hash-algorithm", res, 0);
>>>
>>> This will emit an audit message without the filename when !path.  Is
>>> this what you intended?
>>>
>>
>> This is what I was clumsily trying to explain in the previous comment: if we cannot
>> allocate memory for a file path, I thought it best to log the audit message without
>> the path than fail with a -ENOMEM (auditing will also try to allocate a memory buffer
>> too, but a bit smaller, and memory could have been reclaimed between the two calls,
>> so the auditing operation may succeed).
>>
>> Of course I could also return -ENOMEM, and it would happily propagate back to the user.
>>
>> What do you think ?
> 
> Memory pressure isn't the reason for preventing the xattr write.  It's
> the reason for not being able to audit the setxattr failure.
> 

I completely agree with you, but I'm not quite sure I get the action you want to take
from there.
Does this mean you prefer the mechanism already implemented in this patch (not printing
the file path and trying to audit the setxattr failure anyway)?

> thanks,
> 
> Mimi
> 

  reply	other threads:[~2021-07-28 12:53 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 16:33 [PATCH v4 0/5] IMA: restrict the accepted digest algorithms for THOBY Simon
2021-07-27 16:33 ` [PATCH v4 1/5] IMA: remove the dependency on CRYPTO_MD5 THOBY Simon
2021-07-27 17:57   ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 2/5] IMA: block writes of the security.ima xattr with unsupported algorithms THOBY Simon
2021-07-27 20:32   ` Mimi Zohar
2021-07-28  7:00     ` THOBY Simon
2021-07-28 12:43       ` Mimi Zohar
2021-07-28 12:53         ` THOBY Simon [this message]
2021-07-28 13:09           ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 3/5] IMA: add support to restrict the hash algorithms used for file appraisal THOBY Simon
2021-07-27 20:38   ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 4/5] IMA: add a policy option to restrict xattr hash algorithms on appraisal THOBY Simon
2021-07-27 21:07   ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 5/5] IMA: introduce a new policy option func=SETXATTR_CHECK THOBY Simon
2021-07-27 17:25   ` Mimi Zohar
2021-07-27 17:58     ` THOBY Simon
2021-07-27 17:47 ` [PATCH v4 0/5] IMA: restrict the accepted digest algorithms for Mimi Zohar

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