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

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

[Shaohua Li]

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.

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;
 		}
 	}
 

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

[Steven Rostedt]

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;
>  		}
>  	}
>  
> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

[tip:perf/urgent] tracing: Fix an unallocated memory access in function_graph

[tip-bot for Shaohua Li]

Commit-ID:  575570f02761bd680ba5731c1dfd4701062e7fb2
Gitweb:     http://git.kernel.org/tip/575570f02761bd680ba5731c1dfd4701062e7fb2
Author:     Shaohua Li <shaohua.li@intel.com>
AuthorDate: Tue, 27 Jul 2010 16:06:34 +0800
Committer:  Steven Rostedt <rostedt@goodmis.org>
CommitDate: Fri, 6 Aug 2010 12:19:15 -0400

tracing: Fix an unallocated memory access in function_graph

With CONFIG_DEBUG_PAGEALLOC, I observed an 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 the page size
and touches an unallocated page.

Cc: <stable@kernel.org>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
LKML-Reference: <1280217994.32400.76.camel@sli10-desk.sh.intel.com>
[ Added a comment to explain the problem - SDR ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace_functions_graph.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 79f4bac..b4c179a 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -507,7 +507,15 @@ get_return_for_leaf(struct trace_iterator *iter,
 			 * if the output fails.
 			 */
 			data->ent = *curr;
-			data->ret = *next;
+			/*
+			 * If the next event is not a return type, then
+			 * we only care about what type it is. Otherwise we can
+			 * safely copy the entire event.
+			 */
+			if (next->ent.type == TRACE_GRAPH_RET)
+				data->ret = *next;
+			else
+				data->ret.ent.type = next->ent.type;
 		}
 	}