linux-kernel - Re: [PATCH 05/20] tomoyo_write_control(): get rid of pointless access

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Date:   Sun, 10 May 2020 09:50:58 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Al Viro <viro@...IV.linux.org.uk>, linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 05/20] tomoyo_write_control(): get rid of pointless
 access_ok()

Hello, Al.

I think that this access_ok() check helps reducing partial writes (either
"whole amount was processed" or "not processed at all" unless -ENOMEM).
Do you think that such attempt is pointless? Then, please go ahead...

On 2020/05/10 8:45, Al Viro wrote:
> From: Al Viro <viro@...iv.linux.org.uk>
> 
> address is passed only to get_user()
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  security/tomoyo/common.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
> index 1b467381986f..f93f8acd05f7 100644
> --- a/security/tomoyo/common.c
> +++ b/security/tomoyo/common.c
> @@ -2662,8 +2662,6 @@ ssize_t tomoyo_write_control(struct tomoyo_io_buffer *head,
>  
>  	if (!head->write)
>  		return -EINVAL;
> -	if (!access_ok(buffer, buffer_len))
> -		return -EFAULT;
>  	if (mutex_lock_interruptible(&head->io_sem))
>  		return -EINTR;
>  	head->read_user_buf_avail = 0;
>