diff options
author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2009-05-18 19:35:34 +0800 |
---|---|---|
committer | Frederic Weisbecker <fweisbec@gmail.com> | 2009-05-25 23:53:41 +0200 |
commit | 4f5359685af6de7dca101393dc606620adbe963f (patch) | |
tree | 1f9dc3fb9299008daa6a5fb6f03945008ea4a4f9 /kernel | |
parent | 5537937696c55530447c20aa27daccb8d0d29b33 (diff) | |
download | linux-4f5359685af6de7dca101393dc606620adbe963f.tar.bz2 |
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')
-rw-r--r-- | kernel/trace/trace.c | 8 | ||||
-rw-r--r-- | kernel/trace/trace_output.c | 25 | ||||
-rw-r--r-- | 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 dd40d2320346..02d32baa23ac 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 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; } diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h index 6e220a8e5706..ac240e76eb01 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, |