linux-kernel - Re: [PATCH 4/6] fuse: enable close

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Date:	Fri, 22 Aug 2014 16:04:10 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <MPatlasov@...allels.com>
Cc:	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Anand Avati <avati@...ster.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] fuse: enable close_wait synchronous release

On Thu, Aug 21, 2014 at 6:09 PM, Maxim Patlasov <MPatlasov@...allels.com> wrote:
> The patch enables the feature by passing 'true' to fuse_file_put in
> fuse_release_common.
>
> Previously, this was safe only in special cases when we sure that
> multi-threaded userspace won't deadlock if we'll synchronously send
> FUSE_RELEASE in the context of read-ahead or write-back callback. Now, it's
> always safe because callbacks don't send requests to userspace anymore.

But we do want to make this privileged, as there are unlikely but
possible DoS scenarios with a sync release.

Thanks,
Miklos

>
> Signed-off-by: Maxim Patlasov <mpatlasov@...allels.com>
> ---
>  fs/fuse/file.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 73bce1b..cd55488 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -333,7 +333,8 @@ void fuse_release_common(struct file *file, int opcode)
>          * synchronous RELEASE is allowed (and desirable) in this case
>          * because the server can be trusted not to screw up.
>          */
> -       fuse_file_put(ff, ff->fc->destroy_req != NULL);
> +       fuse_file_put(ff, ff->fc->destroy_req != NULL ||
> +                         must_release_synchronously(ff));
>  }
>
>  static int fuse_open(struct inode *inode, struct file *file)
>
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