tracing/filters: fix race between filter setting and module unload

Module unload is protected by event_mutex, while setting filter is
protected by filter_mutex. This leads to the race:

echo 'bar == 0 || bar == 10' \    |
		> sample/filter   |
                                  |  insmod sample.ko
  add_pred("bar == 0")            |
    -> n_preds == 1               |
  add_pred("bar == 100")          |
    -> n_preds == 2               |
                                  |  rmmod sample.ko
                                  |  insmod sample.ko
  add_pred("&&")                  |
    -> n_preds == 1 (should be 3) |

Now event->filter->preds is corrupted. An then when filter_match_preds()
is called, the WARN_ON() in it will be triggered.

To avoid the race, we remove filter_mutex, and replace it with event_mutex.

[ Impact: prevent corruption of filters by module removing and loading ]

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A375A4D.6000205@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 10 insertions, 17 deletions

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index d9f01c1a042b..936c621bbf46 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -27,8 +27,6 @@
 #include "trace.h"
 #include "trace_output.h"
 
-static DEFINE_MUTEX(filter_mutex);
-
 enum filter_op_ids
 {
         OP_OR,
@@ -294,12 +292,12 @@ void print_event_filter(struct ftrace_event_call *call, struct trace_seq *s)
 {
         struct event_filter *filter = call->filter;
 
-        mutex_lock(&filter_mutex);
+        mutex_lock(&event_mutex);
         if (filter->filter_string)
                 trace_seq_printf(s, "%s\n", filter->filter_string);
         else
                 trace_seq_printf(s, "none\n");
-        mutex_unlock(&filter_mutex);
+        mutex_unlock(&event_mutex);
 }
 
 void print_subsystem_event_filter(struct event_subsystem *system,
@@ -307,12 +305,12 @@ void print_subsystem_event_filter(struct event_subsystem *system,
 {
         struct event_filter *filter = system->filter;
 
-        mutex_lock(&filter_mutex);
+        mutex_lock(&event_mutex);
         if (filter->filter_string)
                 trace_seq_printf(s, "%s\n", filter->filter_string);
         else
                 trace_seq_printf(s, "none\n");
-        mutex_unlock(&filter_mutex);
+        mutex_unlock(&event_mutex);
 }
 
 static struct ftrace_event_field *
@@ -434,7 +432,6 @@ static void filter_free_subsystem_preds(struct event_subsystem *system)
                 filter->n_preds = 0;
         }
 
-        mutex_lock(&event_mutex);
         list_for_each_entry(call, &ftrace_events, list) {
                 if (!call->define_fields)
                         continue;
@@ -444,7 +441,6 @@ static void filter_free_subsystem_preds(struct event_subsystem *system)
                         remove_filter_string(call->filter);
                 }
         }
-        mutex_unlock(&event_mutex);
 }
 
 static int filter_add_pred_fn(struct filter_parse_state *ps,
@@ -631,7 +627,6 @@ static int filter_add_subsystem_pred(struct filter_parse_state *ps,
         filter->preds[filter->n_preds] = pred;
         filter->n_preds++;
 
-        mutex_lock(&event_mutex);
         list_for_each_entry(call, &ftrace_events, list) {
 
                 if (!call->define_fields)
@@ -642,14 +637,12 @@ static int filter_add_subsystem_pred(struct filter_parse_state *ps,
 
                 err = filter_add_pred(ps, call, pred);
                 if (err) {
-                        mutex_unlock(&event_mutex);
                         filter_free_subsystem_preds(system);
                         parse_error(ps, FILT_ERR_BAD_SUBSYS_FILTER, 0);
                         goto out;
                 }
                 replace_filter_string(call->filter, filter_string);
         }
-        mutex_unlock(&event_mutex);
 out:
         return err;
 }
@@ -1076,12 +1069,12 @@ int apply_event_filter(struct ftrace_event_call *call, char *filter_string)
 
         struct filter_parse_state *ps;
 
-        mutex_lock(&filter_mutex);
+        mutex_lock(&event_mutex);
 
         if (!strcmp(strstrip(filter_string), "0")) {
                 filter_disable_preds(call);
                 remove_filter_string(call->filter);
-                mutex_unlock(&filter_mutex);
+                mutex_unlock(&event_mutex);
                 return 0;
         }
 
@@ -1109,7 +1102,7 @@ out:
         postfix_clear(ps);
         kfree(ps);
 out_unlock:
-        mutex_unlock(&filter_mutex);
+        mutex_unlock(&event_mutex);
 
         return err;
 }
@@ -1121,12 +1114,12 @@ int apply_subsystem_event_filter(struct event_subsystem *system,
 
         struct filter_parse_state *ps;
 
-        mutex_lock(&filter_mutex);
+        mutex_lock(&event_mutex);
 
         if (!strcmp(strstrip(filter_string), "0")) {
                 filter_free_subsystem_preds(system);
                 remove_filter_string(system->filter);
-                mutex_unlock(&filter_mutex);
+                mutex_unlock(&event_mutex);
                 return 0;
         }
 
@@ -1154,7 +1147,7 @@ out:
         postfix_clear(ps);
         kfree(ps);
 out_unlock:
-        mutex_unlock(&filter_mutex);
+        mutex_unlock(&event_mutex);
 
         return err;
 }