Re: [RFC] trace_events: Fix kernel crash while using empty filter with perf

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 20 Apr 2018 20:37:58 +0530
Ravi Bangoria <ravi.bangoria@linux.ibm.com> wrote:

> 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
>   #
> 
> Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>

With my initial testing, this looks like a proper fix.

I'll investigate further, and if you don't hear back from me, it means
that I took it.

I'm still waiting on one other patch before I start the process of
testing my current queue to push to Linus. Once I have that one, I'll
start testing my queue, and if I take this, it will be part of it.

Thanks!

-- Steve


> ---
>  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;
>  }