Re: [RFC]ftrace: fix a unallocated memory access in function_graph

[Steven Rostedt <rostedt@goodmis.org>]

Sorry for the late response, I just got back from vacation.

Also note, please do not send to my RH account. I do not check it as
much. Send emails to me to this (goodmis) account.


On Tue, 2010-07-27 at 16:06 +0800, Shaohua Li wrote:
> With CONFIG_DEBUG_PAGEALLOC, I observed a unallocated memory access in
> function_graph trace. It appears we find a small size entry in ring buffer, but
> we access it as a big size entry. The access overflows a page size and touch
> a unallocated page.

Nice catch! This is a legit bug. I'll prepare it for 2.6.36, as well as
send it off to stable.

Thanks!

-- Steve

> 
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> 
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 79f4bac..33b379d 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -507,7 +507,10 @@ get_return_for_leaf(struct trace_iterator *iter,
>  			 * if the output fails.
>  			 */
>  			data->ent = *curr;
> -			data->ret = *next;
> +			if (next->ent.type == TRACE_GRAPH_RET)
> +				data->ret = *next;
> +			else
> +				data->ret.ent.type = next->ent.type;
>  		}
>  	}
>  
> 
> 
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