Re: [PATCH] tracing: Move destroy_actions() before destroy_hist_fields()

[Tom Zanussi]

Hi Steve,

On Wed, 2019-03-20 at 12:53 -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> The destroy_actions() function will call track_data_destroy() which
> calls
> destroy_hist_field() on the data->track_data.var_ref. This checks the
> hist_field flags for HIST_FIELD_FL_VAR_REF, and if it is set it will
> not
> free the variable as it will be freed later.
> 
> destroy_hist_fields() frees the hist_fields that are marked with
> HIST_FIELD_VAR_REF.
> 
> The issue is that destroy_hist_fields() is called before
> destroy_actions()
> and frees the data->track_data.var_ref before destroy_actions() is
> called.
> When the destroy_hist_field() checks the hist_field's flag for
> HIST_FIELD_FL_VAR_REF, the hist_field has already been freed, and
> KASAN
> reports a "used after free" warning:
> 
> ==================================================================
> BUG: KASAN: use-after-free in destroy_hist_field+0x30/0x70
> Read of size 8 at addr ffff888086df2210 by task bash/1694
> 
> CPU: 6 PID: 1694 Comm: bash Not tainted 5.1.0-rc1-test+ #15
> Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01
> v03.03
> 07/14/2016
> Call Trace:
>  dump_stack+0x71/0xa0
>  ? destroy_hist_field+0x30/0x70
>  print_address_description.cold.3+0x9/0x1fb
>  ? destroy_hist_field+0x30/0x70
>  ? destroy_hist_field+0x30/0x70
>  kasan_report.cold.4+0x1a/0x33
>  ? __kasan_slab_free+0x100/0x150
>  ? destroy_hist_field+0x30/0x70
>  destroy_hist_field+0x30/0x70
>  track_data_destroy+0x55/0xe0
>  destroy_hist_data+0x1f0/0x350
>  hist_unreg_all+0x203/0x220
>  event_trigger_open+0xbb/0x130
>  do_dentry_open+0x296/0x700
>  ? stacktrace_count_trigger+0x30/0x30
>  ? generic_permission+0x56/0x200
>  ? __x64_sys_fchdir+0xd0/0xd0
>  ? inode_permission+0x55/0x200
>  ? security_inode_permission+0x18/0x60
>  path_openat+0x633/0x22b0
>  ? path_lookupat.isra.50+0x420/0x420
>  ? __kasan_kmalloc.constprop.12+0xc1/0xd0
>  ? kmem_cache_alloc+0xe5/0x260
>  ? getname_flags+0x6c/0x2a0
>  ? do_sys_open+0x149/0x2b0
>  ? do_syscall_64+0x73/0x1b0
>  ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
>  ? _raw_write_lock_bh+0xe0/0xe0
>  ? __kernel_text_address+0xe/0x30
>  ? unwind_get_return_address+0x2f/0x50
>  ? __list_add_valid+0x2d/0x70
>  ? deactivate_slab.isra.62+0x1f4/0x5a0
>  ? getname_flags+0x6c/0x2a0
>  ? set_track+0x76/0x120
>  do_filp_open+0x11a/0x1a0
>  ? may_open_dev+0x50/0x50
>  ? _raw_spin_lock+0x7a/0xd0
>  ? _raw_write_lock_bh+0xe0/0xe0
>  ? __alloc_fd+0x10f/0x200
>  do_sys_open+0x1db/0x2b0
>  ? filp_open+0x50/0x50
>  do_syscall_64+0x73/0x1b0
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7fa7b24a4ca2
> Code: 25 00 00 41 00 3d 00 00 41 00 74 4c 48 8d 05 85 7a 0d 00 8b 00
> 85 c0
> 75 6d 89 f2 b8 01 01 00 00 48 89 fe bf 9c ff ff ff 0f 05 <48> 3d 00
> f0 ff ff
> 0f 87 a2 00 00 00 48 8b 4c 24 28 64 48 33 0c 25
> RSP: 002b:00007fffbafb3af0 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000101
> RAX: ffffffffffffffda RBX: 000055d3648ade30 RCX: 00007fa7b24a4ca2
> RDX: 0000000000000241 RSI: 000055d364a55240 RDI: 00000000ffffff9c
> RBP: 00007fffbafb3bf0 R08: 0000000000000020 R09: 0000000000000002
> R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000003 R14: 0000000000000001 R15: 000055d364a55240
> 
> By calling destroy_actions() before destroy_hist_fields() will move
> the
> check before the free.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_hist.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c
> b/kernel/trace/trace_events_hist.c
> index ca46339f3009..c510a0e89623 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -4992,10 +4992,10 @@ static void destroy_hist_data(struct
> hist_trigger_data *hist_data)
>  		return;
>  
>  	destroy_hist_trigger_attrs(hist_data->attrs);
> +	destroy_actions(hist_data);
>  	destroy_hist_fields(hist_data);
>  	tracing_map_destroy(hist_data->map);
>  
> -	destroy_actions(hist_data);
>  	destroy_field_vars(hist_data);
>  	destroy_field_var_hists(hist_data);
>  

I initially couldn't reproduce this, but then realized it was because I
had hit another KASAN bug on bootup, unrelated to tracing (will post
that splat shortly), and that turns off further warnings, so I couldn't
see the var ref warning until I realized that...

Anyway, your patch will work, and I even tested it to verify that, but
I think the patch below more directly fixes the problem.