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

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Message-Id: <1506859691.5691.211.camel@linux.vnet.ibm.com>
Date:   Sun, 01 Oct 2017 08:08:11 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Dave Chinner <david@...morbit.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        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

On Sat, 2017-09-30 at 18:56 -0700, Linus Torvalds wrote:
> 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.

Right, re-introducing the iint->mutex and a new i_generation field in
the iint struct with a separate set of locks should work.  It will be
reset if the file metadata changes (eg. setxattr, chown, chmod).

(We need i_generation for namespacing IMA as well.)

thanks,

Mimi