linux-kernel - Re: [PATCH 1/1] do_truncate needs to increment iversion

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Date:	Fri, 16 Dec 2011 20:40:20 +0200
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 1/1] do_truncate needs to increment iversion

On Thu, Dec 15, 2011 at 11:55 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 14 Dec 2011 18:44:57 +0200
> Dmitry Kasatkin <dmitry.kasatkin@...el.com> wrote:
>
>> IMA/EVM uses iversion to identify if file content has been changed.
>> It has been found that when file is opened, truncated with ftruncate()
>> and then closed, iversion is not updated.
>>
>> This patch adds iversion incrementation to do_truncate().
>
> I confess that I've never really fully understood what i_version is
> supposed to do, so I'm not in any position to comment on where, when
> and why the thing should be updated.
>
> At present it gets updated in file_update_time() so I suppose that
> we're not calling file_update_time() in the ftruncate case, which
> sounds wrong?

What I see from notify_change(), it updates the time...
So what is really missing is incrimination of i_version...

>
> It's notable that file_update_time() will not update i_version if the
> inode has NOCMTIME.  This might be wrong, but one would need to know
> the intent of i_version to be able to say.  Do your files have
> S_NOCMTIME set?

Yes. I saw it and even made a test to verify if is the reason for
i_version not to be updated...
But it was not set.
I have the same feeling that i_version should be updated despite NOCMTIME,
because i_version supposed to work if mounted with "iversion" option....
I think it should not have dependency to other mount options...

>
>> --- a/fs/open.c
>> +++ b/fs/open.c
>> @@ -56,6 +56,8 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
>>               newattrs.ia_valid |= ret | ATTR_FORCE;
>>
>>       mutex_lock(&dentry->d_inode->i_mutex);
>> +     if (IS_I_VERSION(dentry->d_inode))
>> +             inode_inc_iversion(dentry->d_inode);
>>       ret = notify_change(dentry, &newattrs);
>>       mutex_unlock(&dentry->d_inode->i_mutex);
>>       return ret;
>
> With four evaluations, it is time to cache dentry->d_inode in a local.

True...

Thanks..
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