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tracing: Change event_filter_read/write to verify i_private != NULL 

event_filter_read/write() are racy, ftrace_event_call can be already
freed by trace_remove_event_call() callers.

1. Shift mutex_lock(event_mutex) from print/apply_event_filter to
   the callers.

2. Change the callers, event_filter_read() and event_filter_write()
   to read i_private under this mutex and abort if it is NULL.

This fixes nothing, but now we can change debugfs_remove("filter")
callers to nullify ->i_private and fix the the problem.

Link: http://lkml.kernel.org/r/20130726172540.GA3619@redhat.com

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Oleg Nesterov 2013-07-26 19:25:40 +02:00 committed by Steven Rostedt
parent bc6f6b08de
commit e2912b091c
2 changed files with 25 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
kernel/trace/trace_events.c
View File

@ -980,21 +980,28 @@ static ssize_t
event_filter_read(struct file *filp, char __user *ubuf, size_t cnt, event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
loff_t *ppos) loff_t *ppos)
{ {
struct ftrace_event_call *call = filp->private_data; struct ftrace_event_call *call;
struct trace_seq *s; struct trace_seq *s;
int r; int r = -ENODEV;
if (*ppos) if (*ppos)
return 0; return 0;
s = kmalloc(sizeof(*s), GFP_KERNEL); s = kmalloc(sizeof(*s), GFP_KERNEL);
if (!s) if (!s)
return -ENOMEM; return -ENOMEM;
trace_seq_init(s); trace_seq_init(s);
print_event_filter(call, s); mutex_lock(&event_mutex);
r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len); call = event_file_data(filp);
if (call)
print_event_filter(call, s);
mutex_unlock(&event_mutex);
if (call)
r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
kfree(s); kfree(s);
@ -1005,9 +1012,9 @@ static ssize_t
event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt, event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
loff_t *ppos) loff_t *ppos)
{ {
struct ftrace_event_call *call = filp->private_data; struct ftrace_event_call *call;
char *buf; char *buf;
int err; int err = -ENODEV;
if (cnt >= PAGE_SIZE) if (cnt >= PAGE_SIZE)
return -EINVAL; return -EINVAL;
@ -1022,7 +1029,12 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
} }
buf[cnt] = '\0'; buf[cnt] = '\0';
err = apply_event_filter(call, buf); mutex_lock(&event_mutex);
call = event_file_data(filp);
if (call)
err = apply_event_filter(call, buf);
mutex_unlock(&event_mutex);
free_page((unsigned long) buf); free_page((unsigned long) buf);
if (err < 0) if (err < 0)
return err; return err;

17
kernel/trace/trace_events_filter.c
View File

@ -637,17 +637,15 @@ static void append_filter_err(struct filter_parse_state *ps,
free_page((unsigned long) buf); free_page((unsigned long) buf);
} }
/* caller must hold event_mutex */
void print_event_filter(struct ftrace_event_call *call, struct trace_seq *s) void print_event_filter(struct ftrace_event_call *call, struct trace_seq *s)
{ {
struct event_filter *filter; struct event_filter *filter = call->filter;
mutex_lock(&event_mutex);
filter = call->filter;
if (filter && filter->filter_string) if (filter && filter->filter_string)
trace_seq_printf(s, "%s\n", filter->filter_string); trace_seq_printf(s, "%s\n", filter->filter_string);
else else
trace_seq_puts(s, "none\n"); trace_seq_puts(s, "none\n");
mutex_unlock(&event_mutex);
} }
void print_subsystem_event_filter(struct event_subsystem *system, void print_subsystem_event_filter(struct event_subsystem *system,
@ -1841,23 +1839,22 @@ static int create_system_filter(struct event_subsystem *system,
return err; return err;
} }
/* caller must hold event_mutex */
int apply_event_filter(struct ftrace_event_call *call, char *filter_string) int apply_event_filter(struct ftrace_event_call *call, char *filter_string)
{ {
struct event_filter *filter; struct event_filter *filter;
int err = 0; int err;
mutex_lock(&event_mutex);
if (!strcmp(strstrip(filter_string), "0")) { if (!strcmp(strstrip(filter_string), "0")) {
filter_disable(call); filter_disable(call);
filter = call->filter; filter = call->filter;
if (!filter) if (!filter)
goto out_unlock; return 0;
RCU_INIT_POINTER(call->filter, NULL); RCU_INIT_POINTER(call->filter, NULL);
/* Make sure the filter is not being used */ /* Make sure the filter is not being used */
synchronize_sched(); synchronize_sched();
__free_filter(filter); __free_filter(filter);
goto out_unlock; return 0;
} }
err = create_filter(call, filter_string, true, &filter); err = create_filter(call, filter_string, true, &filter);
@ -1884,8 +1881,6 @@ int apply_event_filter(struct ftrace_event_call *call, char *filter_string)
__free_filter(tmp); __free_filter(tmp);
} }
} }
out_unlock:
mutex_unlock(&event_mutex);
return err; return err;
} }