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Date: Tue, 26 May 2009 04:04:46 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: LKML <linux-kernel@...r.kernel.org>,
Lai Jiangshan <laijs@...fujitsu.com>,
Steven Rostedt <rostedt@...dmis.org>,
Li Zefan <lizf@...fujitsu.com>,
Pekka Enberg <penberg@...helsinki.fi>,
Zhaolei <zhaolei@...fujitsu.com>,
Tom Zanussi <tzanussi@...il.com>,
Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 1/5] tracing: add trace_event_read_lock()
From: Lai Jiangshan <laijs@...fujitsu.com>
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@...fujitsu.com>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
LKML-Reference: <4A114806.7090302@...fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
kernel/trace/trace.c | 8 ++++++++
kernel/trace/trace_output.c | 25 ++++++++++++++++++-------
kernel/trace/trace_output.h | 2 ++
3 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dd40d23..02d32ba 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1569,12 +1569,14 @@ static void *s_start(struct seq_file *m, loff_t *pos)
p = s_next(m, p, &l);
}
+ trace_event_read_lock();
return p;
}
static void s_stop(struct seq_file *m, void *p)
{
atomic_dec(&trace_record_cmdline_disabled);
+ trace_event_read_unlock();
}
static void print_lat_help_header(struct seq_file *m)
@@ -1817,6 +1819,7 @@ static int trace_empty(struct trace_iterator *iter)
return 1;
}
+/* Called with trace_event_read_lock() held. */
static enum print_line_t print_trace_line(struct trace_iterator *iter)
{
enum print_line_t ret;
@@ -3008,6 +3011,7 @@ waitagain:
offsetof(struct trace_iterator, seq));
iter->pos = -1;
+ trace_event_read_lock();
while (find_next_entry_inc(iter) != NULL) {
enum print_line_t ret;
int len = iter->seq.len;
@@ -3024,6 +3028,7 @@ waitagain:
if (iter->seq.len >= cnt)
break;
}
+ trace_event_read_unlock();
/* Now copy what we have to the user */
sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
@@ -3146,6 +3151,8 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
goto out_err;
}
+ trace_event_read_lock();
+
/* Fill as many pages as possible. */
for (i = 0, rem = len; i < PIPE_BUFFERS && rem; i++) {
pages[i] = alloc_page(GFP_KERNEL);
@@ -3168,6 +3175,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
trace_seq_init(&iter->seq);
}
+ trace_event_read_unlock();
mutex_unlock(&iter->mutex);
spd.nr_pages = i;
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 489c0e8..7136420 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;
}
diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h
index 6e220a8..ac240e7 100644
--- a/kernel/trace/trace_output.h
+++ b/kernel/trace/trace_output.h
@@ -20,6 +20,8 @@ extern int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
extern int trace_print_context(struct trace_iterator *iter);
extern int trace_print_lat_context(struct trace_iterator *iter);
+extern void trace_event_read_lock(void);
+extern void trace_event_read_unlock(void);
extern struct trace_event *ftrace_find_event(int type);
extern enum print_line_t trace_nop_print(struct trace_iterator *iter,
--
1.6.2.3
--
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