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

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Message-ID: <CA+55aFzZXBBn+HgLD_4C6DgpSiOMAP2WzuGPWRUkEXZJuz+QBQ@mail.gmail.com>
Date:   Thu, 28 Sep 2017 20:26:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     Dave Chinner <david@...morbit.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-integrity@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, "Theodore Ts'o" <tytso@....edu>
Subject: Re: [RFC PATCH 3/3] fs: detect that the i_rwsem has already been
 taken exclusively

On Thu, Sep 28, 2017 at 6:53 PM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
>
> The locking issue isn't with validating the file hash, but with the
> setxattr, chmod, chown syscalls.  Each of these syscalls takes the
> i_rwsem exclusively before IMA (or EVM) is called.

Read my email again.

> In setxattr, chmod, chown syscalls, IMA (and EVM) are called after the
> i_rwsem is already taken.  So the locking would be:
>
> lock: i_rwsem
> lock: iint->mutex

No.

Two locks. One inner, one outer. Only the actual ones that calculates
the hash would take the outer one. Read my email.

           Linus