(2013/07/27 2:25), Oleg Nesterov wrote:
> trace_format_open() and trace_format_seq_ops are racy, nothing
> protects ftrace_event_call from trace_remove_event_call().
>
> Change f_start() to take event_mutex and verify i_private != NULL,
> change f_stop() to drop this lock.
>
> This fixes nothing, but now we can change debugfs_remove("format")
> callers to nullify ->i_private and fix the the problem.
>
> Note: the usage of event_mutex is sub-optimal but simple, we can
> change this later.
>
Looks good for me.
Reviewed-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
Thanks!
> Signed-off-by: Oleg Nesterov <o...@redhat.com>
> ---
> kernel/trace/trace_events.c | 13 +++++++++----
> 1 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index b5144c4..3de2aca 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -839,7 +839,7 @@ enum {
>
> static void *f_next(struct seq_file *m, void *v, loff_t *pos)
> {
> - struct ftrace_event_call *call = m->private;
> + struct ftrace_event_call *call = event_file_data(m->private);
> struct list_head *common_head = &ftrace_common_fields;
> struct list_head *head = trace_get_fields(call);
> struct list_head *node = v;
> @@ -871,7 +871,7 @@ static void *f_next(struct seq_file *m, void *v, loff_t
> *pos)
>
> static int f_show(struct seq_file *m, void *v)
> {
> - struct ftrace_event_call *call = m->private;
> + struct ftrace_event_call *call = event_file_data(m->private);
> struct ftrace_event_field *field;
> const char *array_descriptor;
>
> @@ -924,6 +924,11 @@ static void *f_start(struct seq_file *m, loff_t *pos)
> void *p = (void *)FORMAT_HEADER;
> loff_t l = 0;
>
> + /* ->stop() is called even if ->start() fails */
> + mutex_lock(&event_mutex);
> + if (!event_file_data(m->private))
> + return ERR_PTR(-ENODEV);
> +
> while (l < *pos && p)
> p = f_next(m, p, &l);
>
> @@ -932,6 +937,7 @@ static void *f_start(struct seq_file *m, loff_t *pos)
>
> static void f_stop(struct seq_file *m, void *p)
> {
> + mutex_unlock(&event_mutex);
> }
>
> static const struct seq_operations trace_format_seq_ops = {
> @@ -943,7 +949,6 @@ static const struct seq_operations trace_format_seq_ops =
> {
>
> static int trace_format_open(struct inode *inode, struct file *file)
> {
> - struct ftrace_event_call *call = inode->i_private;
> struct seq_file *m;
> int ret;
>
> @@ -952,7 +957,7 @@ static int trace_format_open(struct inode *inode, struct
> file *file)
> return ret;
>
> m = file->private_data;
> - m->private = call;
> + m->private = file;
>
> return 0;
> }
>
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu...@hitachi.com
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