linux-kernel - Re: [PATCH] tracing: use seq_buf_used() in seq_buf_to

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Date:	Wed, 23 Dec 2015 11:09:30 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jerry Snitselaar <jsnitsel@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: use seq_buf_used() in seq_buf_to_user()
 instead of len

On Mon, 16 Nov 2015 12:57:28 -0700
Jerry Snitselaar <jsnitsel@...hat.com> wrote:

> commit 5ac48378414d ("tracing: Use trace_seq_used() and seq_buf_used()
> instead of len") changed the tracing code to use trace_seq_used() and
> seq_buf_used() instead of using the seq_buf len directly to avoid
> overflow issues, but missed a spot in seq_buf_to_user() that makes use
> of s->len.
> 
> Cleaned up the code a bit as well per suggestion of Steve Rostedt.
> 
> Cc: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> Signed-off-by: Jerry Snitselaar <jsnitsel@...hat.com>

I finally got around to applying this. Thanks!

-- Steve

> ---
>  lib/seq_buf.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/seq_buf.c b/lib/seq_buf.c
> index 5c94e10..cb18469 100644
> --- a/lib/seq_buf.c
> +++ b/lib/seq_buf.c
> @@ -306,10 +306,12 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
>  	if (!cnt)
>  		return 0;
>  
> -	if (s->len <= s->readpos)
> +	len = seq_buf_used(s);
> +
> +	if (len <= s->readpos)
>  		return -EBUSY;
>  
> -	len = seq_buf_used(s) - s->readpos;
> +	len -= s->readpos;
>  	if (cnt > len)
>  		cnt = len;
>  	ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);

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