linux-kernel - Re: [RFC PATCH 3/3] fs: detect that the i_rwsem has already been taken exclusively

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Message-ID: <87shf2jzfr.fsf@xmission.com>
Date:   Sun, 01 Oct 2017 17:06:16 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dave Chinner <david@...morbit.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-integrity@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] fs: detect that the i_rwsem has already been taken exclusively

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Sep 30, 2017 18:33, "Eric W. Biederman" <ebiederm@...ssion.com> wrote:.
>
>  That would require a task_work or another kind of work callback so that
>  the writes of the xattr are not synchronous with the vfs callback
>  correct?
>
> No, why?
>
> You should just invalidate the IMA on xattr write or other operations that make the measurement invalid. You only need the inner
> lock.
>
> Why are you guys making up all these things just to make it complicated?

I am not trying to make things complicated I am just trying to
understand the conversation.

Unless I misread something it was being pointed out there are some vfs
operations today on which ima writes an ima xattr as a side effect.  And
those operations hold the i_sem.  So perhaps I am misunderstanding
things or writing the ima xattr needs to happen at some point.  Which
implies something like queued work.

But perhaps I a misunderstanding the conversation and ima.  I frequenly
misunderstand ima.

Eric