tracing/filters: add filter_mutex to protect filter predicates

This patch adds a filter_mutex to prevent the filter predicates from
being accessed concurrently by various external functions.

It's based on a previous patch by Li Zefan:
        "[PATCH 7/7] tracing/filters: make filter preds RCU safe"

v2 changes:

- fixed wrong value returned in a add_subsystem_pred() failure case
  noticed by Li Zefan.

[ Impact: fix trace filter corruption/crashes on parallel access ]

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: paulmck@linux.vnet.ibm.com
LKML-Reference: <1239946028.6639.13.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 75 insertions, 23 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8817c18ef97a..247948e81b08 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -757,13 +757,15 @@ struct filter_pred {
 };
 
 extern void filter_free_pred(struct filter_pred *pred);
-extern void filter_print_preds(struct filter_pred **preds, int n_preds,
+extern void filter_print_preds(struct ftrace_event_call *call,
                                struct trace_seq *s);
 extern int filter_parse(char **pbuf, struct filter_pred *pred);
 extern int filter_add_pred(struct ftrace_event_call *call,
                            struct filter_pred *pred);
 extern void filter_disable_preds(struct ftrace_event_call *call);
 extern void filter_free_subsystem_preds(struct event_subsystem *system);
+extern void filter_print_subsystem_preds(struct event_subsystem *system,
+                                         struct trace_seq *s);
 extern int filter_add_subsystem_pred(struct event_subsystem *system,
                                      struct filter_pred *pred);
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 1137f951be42..64f9d6d2735b 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -488,7 +488,7 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 
         trace_seq_init(s);
 
-        filter_print_preds(call->preds, call->n_preds, s);
+        filter_print_preds(call, s);
         r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
 
         kfree(s);
@@ -558,7 +558,7 @@ subsystem_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 
         trace_seq_init(s);
 
-        filter_print_preds(system->preds, system->n_preds, s);
+        filter_print_subsystem_preds(system, s);
         r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
 
         kfree(s);
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index f8e5eab0424c..e0fcfd2a16d6 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -22,10 +22,13 @@
 #include <linux/uaccess.h>
 #include <linux/module.h>
 #include <linux/ctype.h>
+#include <linux/mutex.h>
 
 #include "trace.h"
 #include "trace_output.h"
 
+static DEFINE_MUTEX(filter_mutex);
+
 static int filter_pred_64(struct filter_pred *pred, void *event)
 {
         u64 *addr = (u64 *)(event + pred->offset);
@@ -112,8 +115,8 @@ int filter_match_preds(struct ftrace_event_call *call, void *rec)
 }
 EXPORT_SYMBOL_GPL(filter_match_preds);
 
-void filter_print_preds(struct filter_pred **preds, int n_preds,
-                        struct trace_seq *s)
+static void __filter_print_preds(struct filter_pred **preds, int n_preds,
+                                 struct trace_seq *s)
 {
         char *field_name;
         struct filter_pred *pred;
@@ -138,6 +141,21 @@ void filter_print_preds(struct filter_pred **preds, int n_preds,
         }
 }
 
+void filter_print_preds(struct ftrace_event_call *call, struct trace_seq *s)
+{
+        mutex_lock(&filter_mutex);
+        __filter_print_preds(call->preds, call->n_preds, s);
+        mutex_unlock(&filter_mutex);
+}
+
+void filter_print_subsystem_preds(struct event_subsystem *system,
+                                  struct trace_seq *s)
+{
+        mutex_lock(&filter_mutex);
+        __filter_print_preds(system->preds, system->n_preds, s);
+        mutex_unlock(&filter_mutex);
+}
+
 static struct ftrace_event_field *
 find_event_field(struct ftrace_event_call *call, char *name)
 {
@@ -180,7 +198,7 @@ static int filter_set_pred(struct filter_pred *dest,
         return 0;
 }
 
-void filter_disable_preds(struct ftrace_event_call *call)
+static void __filter_disable_preds(struct ftrace_event_call *call)
 {
         int i;
 
@@ -190,6 +208,13 @@ void filter_disable_preds(struct ftrace_event_call *call)
                 call->preds[i]->fn = filter_pred_none;
 }
 
+void filter_disable_preds(struct ftrace_event_call *call)
+{
+        mutex_lock(&filter_mutex);
+        __filter_disable_preds(call);
+        mutex_unlock(&filter_mutex);
+}
+
 int init_preds(struct ftrace_event_call *call)
 {
         struct filter_pred *pred;
@@ -223,7 +248,7 @@ oom:
 }
 EXPORT_SYMBOL_GPL(init_preds);
 
-void filter_free_subsystem_preds(struct event_subsystem *system)
+static void __filter_free_subsystem_preds(struct event_subsystem *system)
 {
         struct ftrace_event_call *call;
         int i;
@@ -241,18 +266,25 @@ void filter_free_subsystem_preds(struct event_subsystem *system)
                         continue;
 
                 if (!strcmp(call->system, system->name))
-                        filter_disable_preds(call);
+                        __filter_disable_preds(call);
         }
 }
 
-static int __filter_add_pred(struct ftrace_event_call *call,
-                             struct filter_pred *pred,
-                             filter_pred_fn_t fn)
+void filter_free_subsystem_preds(struct event_subsystem *system)
+{
+        mutex_lock(&filter_mutex);
+        __filter_free_subsystem_preds(system);
+        mutex_unlock(&filter_mutex);
+}
+
+static int filter_add_pred_fn(struct ftrace_event_call *call,
+                              struct filter_pred *pred,
+                              filter_pred_fn_t fn)
 {
         int idx, err;
 
         if (call->n_preds && !pred->compound)
-                filter_disable_preds(call);
+                __filter_disable_preds(call);
 
         if (call->n_preds == MAX_FILTER_PRED)
                 return -ENOSPC;
@@ -276,7 +308,8 @@ static int is_string_field(const char *type)
         return 0;
 }
 
-int filter_add_pred(struct ftrace_event_call *call, struct filter_pred *pred)
+static int __filter_add_pred(struct ftrace_event_call *call,
+                             struct filter_pred *pred)
 {
         struct ftrace_event_field *field;
         filter_pred_fn_t fn;
@@ -293,7 +326,7 @@ int filter_add_pred(struct ftrace_event_call *call, struct filter_pred *pred)
                         return -EINVAL;
                 fn = filter_pred_string;
                 pred->str_len = field->size;
-                return __filter_add_pred(call, pred, fn);
+                return filter_add_pred_fn(call, pred, fn);
         } else {
                 if (pred->str_len)
                         return -EINVAL;
@@ -316,7 +349,18 @@ int filter_add_pred(struct ftrace_event_call *call, struct filter_pred *pred)
                 return -EINVAL;
         }
 
-        return __filter_add_pred(call, pred, fn);
+        return filter_add_pred_fn(call, pred, fn);
+}
+
+int filter_add_pred(struct ftrace_event_call *call, struct filter_pred *pred)
+{
+        int err;
+
+        mutex_lock(&filter_mutex);
+        err = __filter_add_pred(call, pred);
+        mutex_unlock(&filter_mutex);
+
+        return err;
 }
 
 int filter_add_subsystem_pred(struct event_subsystem *system,
@@ -324,20 +368,27 @@ int filter_add_subsystem_pred(struct event_subsystem *system,
 {
         struct ftrace_event_call *call;
 
+        mutex_lock(&filter_mutex);
+
         if (system->n_preds && !pred->compound)
-                filter_free_subsystem_preds(system);
+                __filter_free_subsystem_preds(system);
 
         if (!system->n_preds) {
                 system->preds = kzalloc(MAX_FILTER_PRED * sizeof(pred),
                                         GFP_KERNEL);
-                if (!system->preds)
+                if (!system->preds) {
+                        mutex_unlock(&filter_mutex);
                         return -ENOMEM;
+                }
         }
 
-        if (system->n_preds == MAX_FILTER_PRED)
+        if (system->n_preds == MAX_FILTER_PRED) {
+                mutex_unlock(&filter_mutex);
                 return -ENOSPC;
+        }
 
         system->preds[system->n_preds] = pred;
+        system->n_preds++;
 
         list_for_each_entry(call, &ftrace_events, list) {
                 int err;
@@ -348,17 +399,16 @@ int filter_add_subsystem_pred(struct event_subsystem *system,
                 if (strcmp(call->system, system->name))
                         continue;
 
-                if (!find_event_field(call, pred->field_name))
-                        continue;
-
-                err = filter_add_pred(call, pred);
+                err = __filter_add_pred(call, pred);
                 if (err == -ENOMEM) {
                         system->preds[system->n_preds] = NULL;
+                        system->n_preds--;
+                        mutex_unlock(&filter_mutex);
                         return err;
                 }
         }
 
-        system->n_preds++;
+        mutex_unlock(&filter_mutex);
 
         return 0;
 }