tracing: Fix possible double free in event_enable_trigger_func()

BugLink: http://bugs.launchpad.net/bugs/1815234
commit 15cc78644d0075e76d59476a4467e7143860f660 upstream.

There was a case that triggered a double free in event_trigger_callback()
due to the called reg() function freeing the trigger_data and then it
getting freed again by the error return by the caller. The solution there
was to up the trigger_data ref count.

Code inspection found that event_enable_trigger_func() has the same issue,
but is not as easy to trigger (requires harder to trigger failures). It
needs to be solved slightly different as it needs more to clean up when the
reg() function fails.

Link: http://lkml.kernel.org/r/20180725124008.7008e586@gandalf.local.home
Cc: stable@vger.kernel.org
Fixes: 7862ad1846e99 ("tracing: Add 'enable_event' and 'disable_event' event trigger commands")
Reivewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 8b03635c1b9f56faf01620630caf156f1e9fdfed..55a5b6122847d85b7df06832f1320043aa5e2afd 100644 (file)
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1405,6 +1405,9 @@ int event_enable_trigger_func(struct event_command *cmd_ops,
                goto out;
        }
 
+       /* Up the trigger_data count to make sure nothing frees it on failure */
+       event_trigger_init(trigger_ops, trigger_data);
+
        if (trigger) {
                number = strsep(&trigger, ":");
 
@@ -1455,6 +1458,7 @@ int event_enable_trigger_func(struct event_command *cmd_ops,
                goto out_disable;
        /* Just return zero, not the number of enabled functions */
        ret = 0;
+       event_trigger_free(trigger_ops, trigger_data);
  out:
        return ret;
 
@@ -1465,7 +1469,7 @@ int event_enable_trigger_func(struct event_command *cmd_ops,
  out_free:
        if (cmd_ops->set_filter)
                cmd_ops->set_filter(NULL, trigger_data, NULL);
-       kfree(trigger_data);
+       event_trigger_free(trigger_ops, trigger_data);
        kfree(enable_data);
        goto out;
 }