[v2] ftrace: Fix use-after-free for dynamic ftrace_ops

  KASAN reported a use-after-free with ftrace ops [1]. It was found from
vmcore that perf had registered two ops with the same content
successively, both dynamic. After unregistering the second ops, a
use-after-free occurred.

In ftrace_shutdown(), when the second ops is unregistered, the
FTRACE_UPDATE_CALLS command is not set because there is another enabled
ops with the same content.  Also, both ops are dynamic and the ftrace
callback function is ftrace_ops_list_func, so the
FTRACE_UPDATE_TRACE_FUNC command will not be set. Eventually the value
of 'command' will be 0 and ftrace_shutdown() will skip the rcu
synchronization.

However, ftrace may be activated. When the ops is released, another CPU
may be accessing the ops.  Add the missing synchronization to fix this
problem.

[1]
BUG: KASAN: use-after-free in __ftrace_ops_list_func kernel/trace/ftrace.c:7020 [inline]
BUG: KASAN: use-after-free in ftrace_ops_list_func+0x2b0/0x31c kernel/trace/ftrace.c:7049
Read of size 8 at addr ffff56551965bbc8 by task syz-executor.2/14468

CPU: 1 PID: 14468 Comm: syz-executor.2 Not tainted 5.10.0 #7
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x0/0x40c arch/arm64/kernel/stacktrace.c:132
 show_stack+0x30/0x40 arch/arm64/kernel/stacktrace.c:196
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b4/0x248 lib/dump_stack.c:118
 print_address_description.constprop.0+0x28/0x48c mm/kasan/report.c:387
 __kasan_report mm/kasan/report.c:547 [inline]
 kasan_report+0x118/0x210 mm/kasan/report.c:564
 check_memory_region_inline mm/kasan/generic.c:187 [inline]
 __asan_load8+0x98/0xc0 mm/kasan/generic.c:253
 __ftrace_ops_list_func kernel/trace/ftrace.c:7020 [inline]
 ftrace_ops_list_func+0x2b0/0x31c kernel/trace/ftrace.c:7049
 ftrace_graph_call+0x0/0x4
 __might_sleep+0x8/0x100 include/linux/perf_event.h:1170
 __might_fault mm/memory.c:5183 [inline]
 __might_fault+0x58/0x70 mm/memory.c:5171
 do_strncpy_from_user lib/strncpy_from_user.c:41 [inline]
 strncpy_from_user+0x1f4/0x4b0 lib/strncpy_from_user.c:139
 getname_flags+0xb0/0x31c fs/namei.c:149
 getname+0x2c/0x40 fs/namei.c:209
 [...]

Allocated by task 14445:
 kasan_save_stack+0x24/0x50 mm/kasan/common.c:48
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc mm/kasan/common.c:479 [inline]
 __kasan_kmalloc.constprop.0+0x110/0x13c mm/kasan/common.c:449
 kasan_kmalloc+0xc/0x14 mm/kasan/common.c:493
 kmem_cache_alloc_trace+0x440/0x924 mm/slub.c:2950
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:675 [inline]
 perf_event_alloc.part.0+0xb4/0x1350 kernel/events/core.c:11230
 perf_event_alloc kernel/events/core.c:11733 [inline]
 __do_sys_perf_event_open kernel/events/core.c:11831 [inline]
 __se_sys_perf_event_open+0x550/0x15f4 kernel/events/core.c:11723
 __arm64_sys_perf_event_open+0x6c/0x80 kernel/events/core.c:11723
 [...]

Freed by task 14445:
 kasan_save_stack+0x24/0x50 mm/kasan/common.c:48
 kasan_set_track+0x24/0x34 mm/kasan/common.c:56
 kasan_set_free_info+0x20/0x40 mm/kasan/generic.c:358
 __kasan_slab_free.part.0+0x11c/0x1b0 mm/kasan/common.c:437
 __kasan_slab_free mm/kasan/common.c:445 [inline]
 kasan_slab_free+0x2c/0x40 mm/kasan/common.c:446
 slab_free_hook mm/slub.c:1569 [inline]
 slab_free_freelist_hook mm/slub.c:1608 [inline]
 slab_free mm/slub.c:3179 [inline]
 kfree+0x12c/0xc10 mm/slub.c:4176
 perf_event_alloc.part.0+0xa0c/0x1350 kernel/events/core.c:11434
 perf_event_alloc kernel/events/core.c:11733 [inline]
 __do_sys_perf_event_open kernel/events/core.c:11831 [inline]
 __se_sys_perf_event_open+0x550/0x15f4 kernel/events/core.c:11723
 [...]

Fixes: edb096e00724f ("ftrace: Fix memleak when unregistering dynamic ops when tracing disabled")
Cc: stable@vger.kernel.org
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Li Huafei <lihuafei1@huawei.com>
---
v1: https://lore.kernel.org/lkml/20221101064146.69551-1-lihuafei1@huawei.com/

Changlog in v1 -> v2:
 - Cc the stable list as suggested by Masami. I did not add Masami's
   Review-by due to some differences from v1. If the new changes are
   still okay, please let me know. Thanks to Masami!
 - Add Fixes tag as suggested by Steve.
 - Remove the 'ftrace_enabled' check.

 kernel/trace/ftrace.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)
  

On Thu, 3 Nov 2022 11:10:10 +0800
Li Huafei <lihuafei1@huawei.com> wrote:

> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -3028,18 +3028,8 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command)
>  		command |= FTRACE_UPDATE_TRACE_FUNC;
>  	}
>  
> -	if (!command || !ftrace_enabled) {
> -		/*
> -		 * If these are dynamic or per_cpu ops, they still
> -		 * need their data freed. Since, function tracing is
> -		 * not currently active, we can just free them
> -		 * without synchronizing all CPUs.
> -		 */
> -		if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
> -			goto free_ops;
> -
> -		return 0;
> -	}
> +	if (!command || !ftrace_enabled)
> +		goto out;
>  

Hi Li,

I think you misunderstood me. What I was suggesting was to get rid of
the ftrace_enabled check. The DYNAMIC part is most definitely needed.

	if (!command) {
		if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
			goto out;
		return 0;
	}

-- Steve
  

On Wed, 2 Nov 2022 23:23:34 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> I think you misunderstood me. What I was suggesting was to get rid of
> the ftrace_enabled check. The DYNAMIC part is most definitely needed.
> 
> 	if (!command) {
> 		if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
> 			goto out;
> 		return 0;
> 	}


Nevermind, I forgot that the out is before the DYNAMIC check.

   ;-)

-- Steve
  

On 2022/11/3 11:24, Steven Rostedt wrote:
> On Wed, 2 Nov 2022 23:23:34 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
>> I think you misunderstood me. What I was suggesting was to get rid of
>> the ftrace_enabled check. The DYNAMIC part is most definitely needed.
>>
>> 	if (!command) {
>> 		if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
>> 			goto out;
>> 		return 0;
>> 	}
> 
> 
> Nevermind, I forgot that the out is before the DYNAMIC check.
> 
>    ;-)
> 

Yes. There we have the DYNAMIC check.

> -- Steve
> 
> .
>
  

On Thu, 3 Nov 2022 11:38:30 +0800
Li Huafei <lihuafei1@huawei.com> wrote:

> Yes. There we have the DYNAMIC check.

Yep.

I'm running it now through my tests and if everything goes well (and my
tests don't fail on someone else's bug again), I should have a pull
request ready by tomorrow.

-- Steve
  

On 2022/11/3 12:10, Steven Rostedt wrote:
> On Thu, 3 Nov 2022 11:38:30 +0800
> Li Huafei <lihuafei1@huawei.com> wrote:
> 
>> Yes. There we have the DYNAMIC check.
> 
> Yep.
> 
> I'm running it now through my tests and if everything goes well (and my
> tests don't fail on someone else's bug again), I should have a pull
> request ready by tomorrow.
> 

Thanks!

> -- Steve
> 
> .
>