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authorLai Jiangshan <laijs@cn.fujitsu.com>2009-05-18 15:35:34 +0400
committerFrederic Weisbecker <fweisbec@gmail.com>2009-05-26 01:53:41 +0400
commit4f5359685af6de7dca101393dc606620adbe963f (patch)
tree1f9dc3fb9299008daa6a5fb6f03945008ea4a4f9 /kernel/trace/trace_output.c
parent5537937696c55530447c20aa27daccb8d0d29b33 (diff)
downloadlinux-4f5359685af6de7dca101393dc606620adbe963f.tar.xz
tracing: add trace_event_read_lock()
I found that there is nothing to protect event_hash in ftrace_find_event(). Rcu protects the event hashlist but not the event itself while we use it after its extraction through ftrace_find_event(). This lack of a proper locking in this spot opens a race window between any event dereferencing and module removal. Eg: --Task A-- print_trace_line(trace) { event = find_ftrace_event(trace) --Task B-- trace_module_remove_events(mod) { list_trace_events_module(ev, mod) { unregister_ftrace_event(ev->event) { hlist_del(ev->event->node) list_del(....) } } } |--> module removed, the event has been dropped --Task A-- event->print(trace); // Dereferencing freed memory If the event retrieved belongs to a module and this module is concurrently removed, we may end up dereferencing a data from a freed module. RCU could solve this, but it would add latency to the kernel and forbid tracers output callbacks to call any sleepable code. So this fix converts 'trace_event_mutex' to a read/write semaphore, and adds trace_event_read_lock() to protect ftrace_find_event(). [ Impact: fix possible freed memory dereference in ftrace ] Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Acked-by: Steven Rostedt <rostedt@goodmis.org> LKML-Reference: <4A114806.7090302@cn.fujitsu.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Diffstat (limited to 'kernel/trace/trace_output.c')
-rw-r--r--kernel/trace/trace_output.c25
1 files changed, 18 insertions, 7 deletions
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 489c0e8ada09..7136420603aa 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -14,7 +14,7 @@
/* must be a power of 2 */
#define EVENT_HASHSIZE 128
-static DEFINE_MUTEX(trace_event_mutex);
+static DECLARE_RWSEM(trace_event_mutex);
static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
static int next_event_type = __TRACE_LAST_TYPE + 1;
@@ -466,6 +466,7 @@ static int task_state_char(unsigned long state)
* @type: the type of event to look for
*
* Returns an event of type @type otherwise NULL
+ * Called with trace_event_read_lock() held.
*/
struct trace_event *ftrace_find_event(int type)
{
@@ -475,7 +476,7 @@ struct trace_event *ftrace_find_event(int type)
key = type & (EVENT_HASHSIZE - 1);
- hlist_for_each_entry_rcu(event, n, &event_hash[key], node) {
+ hlist_for_each_entry(event, n, &event_hash[key], node) {
if (event->type == type)
return event;
}
@@ -513,6 +514,16 @@ static int trace_search_list(struct list_head **list)
return last + 1;
}
+void trace_event_read_lock(void)
+{
+ down_read(&trace_event_mutex);
+}
+
+void trace_event_read_unlock(void)
+{
+ up_read(&trace_event_mutex);
+}
+
/**
* register_ftrace_event - register output for an event type
* @event: the event type to register
@@ -533,7 +544,7 @@ int register_ftrace_event(struct trace_event *event)
unsigned key;
int ret = 0;
- mutex_lock(&trace_event_mutex);
+ down_write(&trace_event_mutex);
if (WARN_ON(!event))
goto out;
@@ -581,11 +592,11 @@ int register_ftrace_event(struct trace_event *event)
key = event->type & (EVENT_HASHSIZE - 1);
- hlist_add_head_rcu(&event->node, &event_hash[key]);
+ hlist_add_head(&event->node, &event_hash[key]);
ret = event->type;
out:
- mutex_unlock(&trace_event_mutex);
+ up_write(&trace_event_mutex);
return ret;
}
@@ -597,10 +608,10 @@ EXPORT_SYMBOL_GPL(register_ftrace_event);
*/
int unregister_ftrace_event(struct trace_event *event)
{
- mutex_lock(&trace_event_mutex);
+ down_write(&trace_event_mutex);
hlist_del(&event->node);
list_del(&event->list);
- mutex_unlock(&trace_event_mutex);
+ up_write(&trace_event_mutex);
return 0;
}