ftrace: Have set_graph_functions handle write with RDWR

Since reading the set_graph_functions uses seq functions, which sets the
file->private_data pointer to a seq_file descriptor. On writes the
ftrace_graph_data descriptor is set to file->private_data. But if the file
is opened for RDWR, the ftrace_graph_write() will incorrectly use the
file->private_data descriptor instead of
((struct seq_file *)file->private_data)->private pointer, and this can crash
the kernel.

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b7df0dcf8652d2ee4826b16363f4b13d865b0081..0233c8cb45f4c04649a994ebcaa67fde8e2ed767 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4842,6 +4842,12 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
        if (trace_parser_get_init(&parser, FTRACE_BUFF_MAX))
                return -ENOMEM;
 
+       /* Read mode uses seq functions */
+       if (file->f_mode & FMODE_READ) {
+               struct seq_file *m = file->private_data;
+               fgd = m->private;
+       }
+
        read = trace_get_user(&parser, ubuf, cnt, ppos);
 
        if (read >= 0 && trace_parser_loaded((&parser))) {