Messages in this thread | | | Subject | Re: [PATCH 3/6] tracing: Change event_filter_read/write to verify i_private != NULL | From | Steven Rostedt <> | Date | Wed, 24 Jul 2013 15:52:29 -0400 |
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On Tue, 2013-07-23 at 22:59 +0200, Oleg Nesterov wrote: > 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. Rename print/apply just in case.
I wouldn't do the rename unless there is a print_/apply_ version added later. Just add a comment that event_mutex must be held for those functions.
> > 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. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> > --- > kernel/trace/trace.h | 4 ++-- > kernel/trace/trace_events.c | 28 ++++++++++++++++++---------- > kernel/trace/trace_events_filter.c | 21 ++++++++------------- > 3 files changed, 28 insertions(+), 25 deletions(-) > > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > index afaae41..8b7c72b 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -985,9 +985,9 @@ struct filter_pred { > > extern enum regex_type > filter_parse_regex(char *buff, int len, char **search, int *not); > -extern void print_event_filter(struct ftrace_event_call *call, > +extern void __print_event_filter(struct ftrace_event_call *call, > struct trace_seq *s); > -extern int apply_event_filter(struct ftrace_event_call *call, > +extern int __apply_event_filter(struct ftrace_event_call *call, > char *filter_string); > extern int apply_subsystem_event_filter(struct ftrace_subsystem_dir *dir, > char *filter_string); > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 821768e..0f081c0 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -977,9 +977,9 @@ static ssize_t > event_filter_read(struct file *filp, char __user *ubuf, size_t cnt, > loff_t *ppos) > { > - struct ftrace_event_call *call = filp->private_data; > + struct ftrace_event_call *call; > struct trace_seq *s; > - int r; > + int r = -ENODEV; > > if (*ppos) > return 0; > @@ -987,14 +987,18 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt, > s = kmalloc(sizeof(*s), GFP_KERNEL); > if (!s) > return -ENOMEM; > -
Again, I prefer she space. Just my preference.
> trace_seq_init(s); > > - print_event_filter(call, s); > - r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len); > + mutex_lock(&event_mutex); > + call = event_file_data(filp); > + if (likely(call))
This isn't a fast path. Remove the "likely". It just makes the code ugly.
> + __print_event_filter(call, s); > + mutex_unlock(&event_mutex); > > - kfree(s); > + if (call)
Especially since we have no likely here.
> + r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len); > > + kfree(s); > return r; > } > > @@ -1002,9 +1006,9 @@ static ssize_t > event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt, > loff_t *ppos) > { > - struct ftrace_event_call *call = filp->private_data; > + struct ftrace_event_call *call; > char *buf; > - int err; > + int err = -ENODEV; > > if (cnt >= PAGE_SIZE) > return -EINVAL; > @@ -1019,13 +1023,17 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt, > } > buf[cnt] = '\0'; > > - err = apply_event_filter(call, buf); > + mutex_lock(&event_mutex); > + call = event_file_data(filp); > + if (likely(call))
Again, remove the likely.
> + err = __apply_event_filter(call, buf); > + mutex_unlock(&event_mutex); > + > free_page((unsigned long) buf); > if (err < 0) > return err; > > *ppos += cnt; > - > return cnt; > } > > diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c > index 0c7b75a..71f76ee 100644 > --- a/kernel/trace/trace_events_filter.c > +++ b/kernel/trace/trace_events_filter.c > @@ -637,17 +637,15 @@ static void append_filter_err(struct filter_parse_state *ps, > free_page((unsigned long) buf); > } > > -void print_event_filter(struct ftrace_event_call *call, struct trace_seq *s) > +/* caller must hold event_mutex */ > +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) > trace_seq_printf(s, "%s\n", filter->filter_string); > else > trace_seq_puts(s, "none\n"); > - mutex_unlock(&event_mutex); > } > > void print_subsystem_event_filter(struct event_subsystem *system, > @@ -1841,23 +1839,22 @@ static int create_system_filter(struct event_subsystem *system, > return err; > } > > -int apply_event_filter(struct ftrace_event_call *call, char *filter_string) > +/* caller must hold event_mutex */ > +int __apply_event_filter(struct ftrace_event_call *call, char *filter_string) > { > struct event_filter *filter; > int err = 0;
We can remove the 0 init here.
> > - mutex_lock(&event_mutex); > - > if (!strcmp(strstrip(filter_string), "0")) { > filter_disable(call); > filter = call->filter; > if (!filter) > - goto out_unlock; > + goto out;
Remove the "out" label, and just return 0 here.
> RCU_INIT_POINTER(call->filter, NULL); > /* Make sure the filter is not being used */ > synchronize_sched(); > __free_filter(filter); > - goto out_unlock; > + goto out;
Here too.
> } > > err = create_filter(call, filter_string, true, &filter); > @@ -1884,9 +1881,7 @@ int apply_event_filter(struct ftrace_event_call *call, char *filter_string) > __free_filter(tmp); > } > } > -out_unlock: > - mutex_unlock(&event_mutex); > - > +out: > return err; > } >
-- Steve
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