tracing: only truncate ftrace files when O_TRUNC is set

The current code will truncate the ftrace files contents if O_APPEND
is not set and the file is opened in write mode. This is incorrect.
It should only truncate the file if O_TRUNC is set. Otherwise
if one of these files is opened by a C program with fopen "r+",
it will incorrectly truncate the file.

Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8bc8d8afea6a..d8ef28574aa1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2031,7 +2031,7 @@ static int tracing_open(struct inode *inode, struct file *file)
 
         /* If this file was open for write, then erase contents */
         if ((file->f_mode & FMODE_WRITE) &&
-            !(file->f_flags & O_APPEND)) {
+            (file->f_flags & O_TRUNC)) {
                 long cpu = (long) inode->i_private;
 
                 if (cpu == TRACE_PIPE_ALL_CPU)