linux-kernel - Re: [PATCH 2/3] *: convert stream-like files from nonseekable_open -> stream

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Date:   Wed, 27 Mar 2019 07:54:28 +0100
From:   Lubomir Rintel <lkundrak@...sk>
To:     Kirill Smelkov <kirr@...edi.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] *: convert stream-like files from nonseekable_open
 -> stream_open

On Tue, 2019-03-26 at 23:23 +0000, Kirill Smelkov wrote:
> Using scripts/coccinelle/api/stream_open.cocci added in the previous
> patch, search and convert to stream_open all in-kernel nonseekable_open
> users for which read and write actually do not depend on ppos and where
> there is no other methods in file_operations which assume @offset
> access.
> 
> I've verified each generated change manually - that it is correct to convert -
> and each other nonseekable_open instance left - that it is either not correct
> to convert there, or that it is not converted due to current stream_open.cocci
> limitations. The script also does not convert files that should be valid to
> convert, but that currently have .llseek = noop_llseek or generic_file_llseek
> for unknown reason despite file being opened with nonseekable_open (e.g.
> drivers/input/mousedev.c)
> 
> Among cases converted 14 were potentially vulnerable to read vs write deadlock
> (see details in the previous patch):

...

> and the reset were just safe to convert to stream_open because their
> read and write do not use ppos at all and corresponding file_operations
> do not have methods that assume @offset file access:

...

> 	drivers/char/pcmcia/scr24x_cs.c:95:8-24: WARNING: scr24x_fops: .read() and .write() have stream semantic; safe to change nonseekable_open -> stream_open.

...

> diff --git a/drivers/char/pcmcia/scr24x_cs.c b/drivers/char/pcmcia/scr24x_cs.c
> index f6b43d9350f0..04b39c3596cc 100644
> --- a/drivers/char/pcmcia/scr24x_cs.c
> +++ b/drivers/char/pcmcia/scr24x_cs.c
> @@ -92,7 +92,7 @@ static int scr24x_open(struct inode *inode, struct file *filp)
>  	kref_get(&dev->refcnt);
>  	filp->private_data = dev;
>  
> -	return nonseekable_open(inode, filp);
> +	return stream_open(inode, filp);
>  }
>  
>  static int scr24x_release(struct inode *inode, struct file *filp)

Acked-by: Lubomir Rintel <lkundrak@...sk> [scr24x_cs]

Thanks,
Lubo