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Subject[PATCH 5/5] tracing/filters: fix race between filter setting and module unload
From: Li Zefan <lizf@cn.fujitsu.com>

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>
---
kernel/trace/trace_events_filter.c | 27 ++++++++++-----------------
1 files changed, 10 insertions(+), 17 deletions(-)
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index d9f01c1..936c621 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;
}
--
1.6.3.1
--


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