[PATCH 4.19 2/2] tracing: Remove unnecessary var destroy in onmax_destroy()

[George Guo <dongtai.guo@linux.dev>]

From: George Guo <guodongtai@kylinos.cn>

commit ff9d31d0d46672e201fc9ff59c42f1eef5f00c77 upstream.

The onmax_destroy() destroyed the onmax var, casusing a double-free error
flagged by KASAN.

This is tested via "./ftracetest test.d/trigger/inter-event/
trigger-onmatch-onmax-action-hist.tc".

==================================================================
BUG: KASAN: use-after-free in destroy_hist_field+0x1c2/0x200
Read of size 8 at addr ffff88800a4ad100 by task ftracetest/4731

CPU: 0 PID: 4731 Comm: ftracetest Kdump: loaded Tainted: GE 4.19.90-89 #77
Source Version: Unknown
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0
Call Trace:
 dump_stack+0xcb/0x10b
 print_address_description.cold+0x54/0x249
 kasan_report_error.cold+0x63/0xab
 ? destroy_hist_field+0x1c2/0x200
 ? hist_trigger_elt_data_alloc+0x5a0/0x5a0
 __asan_report_load8_noabort+0x8d/0xa0
 ? destroy_hist_field+0x1c2/0x200
 destroy_hist_field+0x1c2/0x200
 onmax_destroy+0x72/0x1e0
 ? hist_trigger_elt_data_alloc+0x5a0/0x5a0
 destroy_hist_data+0x236/0xa40
 event_hist_trigger_free+0x212/0x2f0
 ? update_cond_flag+0x128/0x170
 ? event_hist_trigger_func+0x2880/0x2880
 hist_unregister_trigger+0x2f2/0x4f0
 event_hist_trigger_func+0x168c/0x2880
 ? tracing_map_cmp_u64+0xa0/0xa0
 ? onmatch_create.constprop.0+0xf50/0xf50
 ? __mutex_lock_slowpath+0x10/0x10
 event_trigger_write+0x2f4/0x490
 ? trigger_start+0x180/0x180
 ? __fget_light+0x369/0x5d0
 ? count_memcg_event_mm+0x104/0x2b0
 ? trigger_start+0x180/0x180
 __vfs_write+0x81/0x100
 vfs_write+0x1e1/0x540
 ksys_write+0x12a/0x290
 ? __ia32_sys_read+0xb0/0xb0
 ? __close_fd+0x1d3/0x280
 do_syscall_64+0xe3/0x2d0
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1
RIP: 0033:0x7fd7f4c44e04
Code: 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 
48 8d 05 39 34 0c 00 8b 00 85 c0 75 13 b8 01 00 00 00 0f 05 <48> 3d 00 
f0 ff ff 77 54 f3 c3 66 90 41 54 55 49 89 d4 53 48 89 f5
RSP: 002b:00007fff10370df8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000000010f RCX: 00007fd7f4c44e04
RDX: 000000000000010f RSI: 000055fa765df650 RDI: 0000000000000001
RBP: 000055fa765df650 R08: 000000000000000a R09: 0000000000000000
R10: 000000000000000a R11: 0000000000000246 R12: 00007fd7f4d035c0
R13: 000000000000010f R14: 00007fd7f4d037c0 R15: 000000000000010f
==================================================================

So remove the onmax_destroy() destroy_hist_field() call for that var.

Fixes: 50450603ec9c("tracing: Add 'onmax' hist trigger action support")
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 kernel/trace/trace_events_hist.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 7dcb96305e56..58b8a2575b8c 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -337,7 +337,6 @@ struct action_data {
 			char			*fn_name;
 			unsigned int		max_var_ref_idx;
 			struct hist_field	*max_var;
-			struct hist_field	*var;
 		} onmax;
 	};
 };
@@ -3489,7 +3488,6 @@ static void onmax_destroy(struct action_data *data)
 	unsigned int i;
 
 	destroy_hist_field(data->onmax.max_var, 0);
-	destroy_hist_field(data->onmax.var, 0);
 
 	kfree(data->onmax.var_str);
 	kfree(data->onmax.fn_name);
@@ -3528,8 +3526,6 @@ static int onmax_create(struct hist_trigger_data *hist_data,
 	if (!ref_field)
 		return -ENOMEM;
 
-	data->onmax.var = ref_field;
-
 	data->fn = onmax_save;
 	data->onmax.max_var_ref_idx = var_ref_idx;
 	max_var = create_var(hist_data, file, "max", sizeof(u64), "u64");
-- 
2.34.1