linux-kernel - Re: [PATCH 2/2] tracing: Fix kmemleak in set_trigger

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Date:   Wed, 23 Aug 2017 12:52:49 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Chunyu Hu <chuhu@...hat.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] tracing: Fix kmemleak in set_trigger_filter

On Wed, 23 Aug 2017 10:41:55 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

>  * On success, returns 0 and *@...terp points to the new filter.  On
>  * failure, returns -errno and *@...terp may point to %NULL or to a new
>  * filter.  In the latter case, the returned filter contains error
>  * information if @set_str is %true and the caller is responsible for
>  * freeing it.
> 
> So filter contains an error string when it fails. It seems that we
> should somehow propagate that up the chain to display. I'll look more
> into this.

The bug is in create_filter(), because "set_str" is set to false, and
the filter should not be passed back allocated on error.

The correct fix is below.

Thanks!

-- Steve


>From 9975be0b2dccaea8ec3574d69a3504e11659a6ea Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Date: Wed, 23 Aug 2017 12:46:27 -0400
Subject: [PATCH] tracing: Fix freeing of filter in create_filter() when
 set_str is false

Performing the following task with kmemleak enabled:

 # cd /sys/kernel/tracing/events/irq/irq_handler_entry/
 # echo 'enable_event:kmem:kmalloc:3 if irq >' > trigger
 # echo 'enable_event:kmem:kmalloc:3 if irq > 31' > trigger
 # echo scan > /sys/kernel/debug/kmemleak
 # cat /sys/kernel/debug/kmemleak
unreferenced object 0xffff8800b9290308 (size 32):
  comm "bash", pid 1114, jiffies 4294848451 (age 141.139s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff81cef5aa>] kmemleak_alloc+0x4a/0xa0
    [<ffffffff81357938>] kmem_cache_alloc_trace+0x158/0x290
    [<ffffffff81261c09>] create_filter_start.constprop.28+0x99/0x940
    [<ffffffff812639c9>] create_filter+0xa9/0x160
    [<ffffffff81263bdc>] create_event_filter+0xc/0x10
    [<ffffffff812655e5>] set_trigger_filter+0xe5/0x210
    [<ffffffff812660c4>] event_enable_trigger_func+0x324/0x490
    [<ffffffff812652e2>] event_trigger_write+0x1a2/0x260
    [<ffffffff8138cf87>] __vfs_write+0xd7/0x380
    [<ffffffff8138f421>] vfs_write+0x101/0x260
    [<ffffffff8139187b>] SyS_write+0xab/0x130
    [<ffffffff81cfd501>] entry_SYSCALL_64_fastpath+0x1f/0xbe
    [<ffffffffffffffff>] 0xffffffffffffffff

The function create_filter() is passed a 'filterp' pointer that gets
allocated, and if "set_str" is true, it is up to the caller to free it, even
on error. The problem is that the pointer is not freed by create_filter()
when set_str is false. This is a bug, and it is not up to the caller to free
the filter on error if it doesn't care about the string.

Link: http://lkml.kernel.org/r/1502705898-27571-2-git-send-email-chuhu@redhat.com

Reported-by: Chunyu Hu <chuhu@...hat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_filter.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 59a411f..181e139 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1959,6 +1959,10 @@ static int create_filter(struct trace_event_call *call,
 		if (err && set_str)
 			append_filter_err(ps, filter);
 	}
+	if (err && !set_str) {
+		free_event_filter(filter);
+		filter = NULL;
+	}
 	create_filter_finish(ps);
 
 	*filterp = filter;
-- 
2.9.5