linux-kernel - Re: [PATCH] tracing/profile: Fix profile_disable vs module

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 25 Aug 2009 13:22:13 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

>>>>>> If the correspoding module is unloaded before ftrace_profile_disable()
>>>>>> is called, event->profile_disable() won't be called, which can
>>>>>> cause oops:
>>>>>>
>>>>>>   # insmod trace-events-sample.ko
>>>>>>   # perf record -f -a -e sample:foo_bar sleep 3 &
>>>>>>   # sleep 1
>>>>>>   # rmmod trace_events_sample
>>>>>>   # insmod trace-events-sample.ko
>>>>>>   OOPS!
>>>>>>
>>>>>> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
>>>>>
>>>>> Hrmm, feel fragile, why don't we check if all a modules tracepoints are
>>>>> unused on unload?
>>>>>
>>>> I don't think it's fragile. We are profiling via a module's
>>>> tracepoint, so we should pin the module, via module_get().
>>>> If event->profile_enable() has been calld, we should make
>>>> sure it's profile_disable() will be called.
>>> What I call fragile is that everyone registering a tracepoint 
>>> callback will now apparently need to worry about modules, _that_ 
>>> is fragile.
>>>
>>> Either make module unload look at tracepoint users, or place the 
>>> try_get_module() in the registration hooks so that regular users 
>>> don't need to worry about it.
>> The bug found by Li needs to be fixed obviously.
>>
>> I tend to agree with you that this does not appear to be the best 
>> place to do it: so you suggest to implicitly increase the module 
>> refcount on callback registr instead? (and releasing it when 
>> unregistering)
>>
>> Same end result, slightly cleaner place to bump the refcount.
> 
> Yes, because the user of tracepoints should never need to care about
> modules.
> 

I'm afraid it is not feasible to bump module refcnt implicitly
in tracepoint_probe_register().

If a tracepoint is registered in module_init, and unregistered
in module_exit (see sample/tracepoints), the module is unloadable:

 insmod
 ->call mod->init()
   ->trace_reg_foo()
     ->module_get()

 rmmod
 ->check mod refcnt
 ->call mod->exit()
   ->trace_unreg_foo()
     ->module_put()
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/