[GIT PULL] tracing: Have filter check for balanced ops

[Steven Rostedt]

Linus,

Vince Weaver reported a warning when he added perf event filters
into his fuzzer tests. There's a missing check of balanced
operations when parenthesis are used, and this triggers a WARN_ON()
and when reading the failure, the filter reports no failure occurred.

The operands were not being checked if they match, this adds that.

Please pull the latest trace-fix-filter-4.1-rc8 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-fix-filter-4.1-rc8

Tag SHA1: 34bcfc82862ee15a76b98c54126f64abf52191c3
Head SHA1: 2cf30dc180cea808077f003c5116388183e54f9e


Steven Rostedt (1):
      tracing: Have filter check for balanced ops

----
 kernel/trace/trace_events_filter.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
---------------------------
commit 2cf30dc180cea808077f003c5116388183e54f9e
Author: Steven Rostedt <rostedt@xxxxxxxxxxx>
Date:   Mon Jun 15 17:50:25 2015 -0400

    tracing: Have filter check for balanced ops
    
    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@xxxxxxxxxxxxxxxxxx
    
    Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
    Cc: Ingo Molnar <mingo@xxxxxxxxxx>
    Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx # 2.6.31+
    Reported-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
    Tested-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
    Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index ced69da0ff55..7f2e97ce71a7 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1369,19 +1369,26 @@ 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;
+		}
 
 		if (elt->op == OP_AND || elt->op == OP_OR) {
 			n_logical_preds++;
+			cnt--;
 			continue;
 		}
+		if (elt->op != OP_NOT)
+			cnt--;
 		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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