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Subject[PATCH 3/7] tracing: Fix kernel crash while using empty filter with perf
From: Ravi Bangoria <ravi.bangoria@linux.ibm.com>

Kernel is crashing when user tries to record 'ftrace:function' event
with empty filter:

# perf record -e ftrace:function --filter="" ls

# dmesg
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
Oops: 0000 [#1] SMP PTI
...
RIP: 0010:ftrace_profile_set_filter+0x14b/0x2d0
RSP: 0018:ffffa4a7c0da7d20 EFLAGS: 00010246
RAX: ffffa4a7c0da7d64 RBX: 0000000000000000 RCX: 0000000000000006
RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8c48ffc968f0
...
Call Trace:
_perf_ioctl+0x54a/0x6b0
? rcu_all_qs+0x5/0x30
...

After patch:
# perf record -e ftrace:function --filter="" ls
failed to set filter "" on event ftrace:function with 22 (Invalid argument)

Also, if user tries to echo "" > filter, it used to throw an error.
This behavior got changed by commit 80765597bc58 ("tracing: Rewrite
filter logic to be simpler and faster"). This patch restores the
behavior as a side effect:

Before patch:
# echo "" > filter
#

After patch:
# echo "" > filter
bash: echo: write error: Invalid argument
#

Link: http://lkml.kernel.org/r/20180420150758.19787-1-ravi.bangoria@linux.ibm.com

Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_events_filter.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 9b4716bb8bb0..1f951b3df60c 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1499,14 +1499,14 @@ static int process_preds(struct trace_event_call *call,
return ret;
}

- if (!nr_preds) {
- prog = NULL;
- } else {
- prog = predicate_parse(filter_string, nr_parens, nr_preds,
+ if (!nr_preds)
+ return -EINVAL;
+
+ prog = predicate_parse(filter_string, nr_parens, nr_preds,
parse_pred, call, pe);
- if (IS_ERR(prog))
- return PTR_ERR(prog);
- }
+ if (IS_ERR(prog))
+ return PTR_ERR(prog);
+
rcu_assign_pointer(filter->prog, prog);
return 0;
}
--
2.16.3

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