tracing: Use trace_seq_used() and seq_buf_used() instead of len

As the seq_buf->len will soon be +1 size when there's an overflow, we
must use trace_seq_used() or seq_buf_used() methods to get the real
length. This will prevent buffer overflow issues if just the len
of the seq_buf descriptor is used to copy memory.

Link: http://lkml.kernel.org/r/20141114121911.09ba3d38@gandalf.local.home

Reported-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 6d1342ae7a44..ec35468349a7 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -1153,6 +1153,9 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
                         return ret;
         }
 
+        if (trace_seq_has_overflowed(s))
+                goto out;
+
         /* Strip ending newline */
         if (s->buffer[s->seq.len - 1] == '\n') {
                 s->buffer[s->seq.len - 1] = '\0';
@@ -1160,7 +1163,7 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
         }
 
         trace_seq_puts(s, " */\n");
-
+ out:
         return trace_handle_return(s);
 }