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SubjectRe: [RFC] trace_events: Fix kernel crash while using empty filter with perf
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;
> }

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