linux-kernel - Re: [PATCH v4] tracing: Fix out of bounds write in get_trace

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Date:   Thu, 29 Oct 2020 14:49:35 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Qiujun Huang <hqjagain@...il.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v4] tracing: Fix out of bounds write in get_trace_buf

On Fri, 30 Oct 2020 00:19:05 +0800
Qiujun Huang <hqjagain@...il.com> wrote:

> The subscript should be nesting - 1, as nesting had self-added.
> 
> Fixes: 3d9622c12c887 ("tracing: Add barrier to trace_printk() buffer nesting modification")

Thanks, I'll still use the updated change log.

-- Steve

> Signed-off-by: Qiujun Huang <hqjagain@...il.com>
> ---
> v4:
> Find the right patch which cause the problem.
> v3:
> Modify the way of array reference instead.
> v2:
> Fix a typo in the title.
> ---
>  kernel/trace/trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 528971714fc6..daa96215e294 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3132,7 +3132,7 @@ static char *get_trace_buf(void)
>  
>  	/* Interrupts must see nesting incremented before we use the buffer */
>  	barrier();
> -	return &buffer->buffer[buffer->nesting][0];
> +	return &buffer->buffer[buffer->nesting - 1][0];
>  }
>  
>  static void put_trace_buf(void)