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SubjectRe: [PATCH 2/2] tracing: Fix kmemleak in set_trigger_filter


----- Original Message -----
> From: "Steven Rostedt" <rostedt@goodmis.org>
> To: "Chunyu Hu" <chuhu@redhat.com>
> Cc: mingo@kernel.org, linux-kernel@vger.kernel.org
> Sent: Wednesday, August 23, 2017 12:52:49 PM
> Subject: Re: [PATCH 2/2] tracing: Fix kmemleak in set_trigger_filter
>
> On Wed, 23 Aug 2017 10:41:55 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > * On success, returns 0 and *@filterp points to the new filter. On
> > * failure, returns -errno and *@filterp 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.

Thanks for all the analysis. I think you are right. I'll try to have a test on it
in case we miss something. But please don't block on my test.

>
> The correct fix is below.
>
> Thanks!
>
> -- Steve
>
>
> From 9975be0b2dccaea8ec3574d69a3504e11659a6ea Mon Sep 17 00:00:00 2001
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.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@redhat.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.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
>
>

--
Regards,
Chunyu Hu

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