linux-kernel - Re: [RFC/PATCH 1/2] pstore: Protect unlink with read

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Message-ID: <CAGXu5jJDHpu0zpFGWS++HEOJCbr6qmdnxW1WWudYf36ed0oZNg@mail.gmail.com>
Date:   Tue, 15 Nov 2016 15:20:56 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [RFC/PATCH 1/2] pstore: Protect unlink with read_mutex

On Tue, Oct 18, 2016 at 6:23 PM, Namhyung Kim <namhyung@...nel.org> wrote:
> When update_ms is set, pstore_get_records() will be called when there's
> a new entry.  But unlink can be called at the same time and might
> contend with the open-read-close loop.  Depending on the implementation
> of platform driver, it may be safe or not.  But I think it'd be better
> to protect those race in the first place.
>
> Cc: Stefan Hajnoczi <stefanha@...hat.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

This looks correct to me, thanks! It should appear in -next shortly...

-Kees

> ---
>  fs/pstore/inode.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
> index 1781dc50762e..75728dfae0a6 100644
> --- a/fs/pstore/inode.c
> +++ b/fs/pstore/inode.c
> @@ -197,11 +197,14 @@ static int pstore_unlink(struct inode *dir, struct dentry *dentry)
>         if (err)
>                 return err;
>
> -       if (p->psi->erase)
> +       if (p->psi->erase) {
> +               mutex_lock(&p->psi->read_mutex);
>                 p->psi->erase(p->type, p->id, p->count,
>                               d_inode(dentry)->i_ctime, p->psi);
> -       else
> +               mutex_unlock(&p->psi->read_mutex);
> +       } else {
>                 return -EPERM;
> +       }
>
>         return simple_unlink(dir, dentry);
>  }
> --
> 2.9.3
>



-- 
Kees Cook
Nexus Security