linux-kernel - Re: [GIT PULL] tracing: Have filter check for balanced ops

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Date:	Mon, 22 Jun 2015 15:49:40 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	stable@...r.kernel.org
Subject: Re: [GIT PULL] tracing: Have filter check for balanced ops

On Mon, Jun 22, 2015 at 10:17:28AM -0400, Steven Rostedt wrote:
...
> To make this patch simpler, just move the "cnt--;" above the OP_AND and
> OP_OR check and remove the "cnt--;" from that if statement.
> 
> But yeah, this looks fine. You can test it with the example in the
> change log.
> 
>   echo "((dev==1)blocks==2)" > events/ext4/ext4_truncate_exit/filter
> 
> And see if it gives an error other than "parse_error: No error".
> 
> -- Steve

Thanks Steven, I've done a quick test with a 3.16-ckt kernel and I can
confirm that the modified patch (i.e. including your suggestion) fixes
the problem.

I'm attaching the patch below and CC'ing stable mailing-list.

Cheers,
--
Luís

>From 19305c2d68fbb43ba219881082b95da2e4e82db5 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@...dmis.org>
Date: Mon, 15 Jun 2015 17:50:25 -0400
Subject: [PATCH] tracing: Have filter check for balanced ops

commit 2cf30dc180cea808077f003c5116388183e54f9e upstream.

When the following filter is used it causes a warning to trigger:

 # cd /sys/kernel/debug/tracing
 # echo "((dev==1)blocks==2)" > events/ext4/ext4_truncate_exit/filter
-bash: echo: write error: Invalid argument
 # cat events/ext4/ext4_truncate_exit/filter
((dev==1)blocks==2)
^
parse_error: No error

 ------------[ cut here ]------------
 WARNING: CPU: 2 PID: 1223 at kernel/trace/trace_events_filter.c:1640 replace_preds+0x3c5/0x990()
 Modules linked in: bnep lockd grace bluetooth  ...
 CPU: 3 PID: 1223 Comm: bash Tainted: G        W       4.1.0-rc3-test+ #450
 Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v02.05 05/07/2012
  0000000000000668 ffff8800c106bc98 ffffffff816ed4f9 ffff88011ead0cf0
  0000000000000000 ffff8800c106bcd8 ffffffff8107fb07 ffffffff8136b46c
  ffff8800c7d81d48 ffff8800d4c2bc00 ffff8800d4d4f920 00000000ffffffea
 Call Trace:
  [<ffffffff816ed4f9>] dump_stack+0x4c/0x6e
  [<ffffffff8107fb07>] warn_slowpath_common+0x97/0xe0
  [<ffffffff8136b46c>] ? _kstrtoull+0x2c/0x80
  [<ffffffff8107fb6a>] warn_slowpath_null+0x1a/0x20
  [<ffffffff81159065>] replace_preds+0x3c5/0x990
  [<ffffffff811596b2>] create_filter+0x82/0xb0
  [<ffffffff81159944>] apply_event_filter+0xd4/0x180
  [<ffffffff81152bbf>] event_filter_write+0x8f/0x120
  [<ffffffff811db2a8>] __vfs_write+0x28/0xe0
  [<ffffffff811dda43>] ? __sb_start_write+0x53/0xf0
  [<ffffffff812e51e0>] ? security_file_permission+0x30/0xc0
  [<ffffffff811dc408>] vfs_write+0xb8/0x1b0
  [<ffffffff811dc72f>] SyS_write+0x4f/0xb0
  [<ffffffff816f5217>] system_call_fastpath+0x12/0x6a
 ---[ end trace e11028bd95818dcd ]---

Worse yet, reading the error message (the filter again) it says that
there was no error, when there clearly was. The issue is that the
code that checks the input does not check for balanced ops. That is,
having an op between a closed parenthesis and the next token.

This would only cause a warning, and fail out before doing any real
harm, but it should still not caues a warning, and the error reported
should work:

 # cd /sys/kernel/debug/tracing
 # echo "((dev==1)blocks==2)" > events/ext4/ext4_truncate_exit/filter
-bash: echo: write error: Invalid argument
 # cat events/ext4/ext4_truncate_exit/filter
((dev==1)blocks==2)
^
parse_error: Meaningless filter expression

And give no kernel warning.

Link: http://lkml.kernel.org/r/20150615175025.7e809215@gandalf.local.home

Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
Tested-by: Vince Weaver <vincent.weaver@...ne.edu>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
[ luis: backported to 3.16:
  - unconditionally decrement cnt as the OP_NOT logic was introduced only
    by e12c09cf3087 ("tracing: Add NOT to filtering logic") ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 kernel/trace/trace_events_filter.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 8a8631926a07..cb347e85f75e 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1399,19 +1399,24 @@ static int check_preds(struct filter_parse_state *ps)
 {
 	int n_normal_preds = 0, n_logical_preds = 0;
 	struct postfix_elt *elt;
+	int cnt = 0;
 
 	list_for_each_entry(elt, &ps->postfix, list) {
-		if (elt->op == OP_NONE)
+		if (elt->op == OP_NONE) {
+			cnt++;
 			continue;
+		}
 
+		cnt--;
 		if (elt->op == OP_AND || elt->op == OP_OR) {
 			n_logical_preds++;
 			continue;
 		}
 		n_normal_preds++;
+		WARN_ON_ONCE(cnt < 0);
 	}
 
-	if (!n_normal_preds || n_logical_preds >= n_normal_preds) {
+	if (cnt != 1 || !n_normal_preds || n_logical_preds >= n_normal_preds) {
 		parse_error(ps, FILT_ERR_INVALID_FILTER, 0);
 		return -EINVAL;
 	}
--
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