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>

1 files changed, 9 insertions, 1 deletions

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 79f4bac99a94..b4c179ae4e45 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;
                 }
         }