On Wed, Oct 23, 2024 at 3:01 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Peter reported that perf_event_detach_bpf_prog might skip to release
> the bpf program for -ENOENT error from bpf_prog_array_copy.
>
> This can't happen because bpf program is stored in perf event and is
> detached and released only when perf event is freed.
>
> Let's make it obvious and add WARN_ON_ONCE on the -ENOENT check and
> make sure the bpf program is released in any case.
>
> Cc: Sean Young <sean@xxxxxxxx>
> Fixes: 170a7e3ea070 ("bpf: bpf_prog_array_copy() should return -ENOENT if exclude_prog not found")
> Closes: https://lore.kernel.org/lkml/20241022111638.GC16066@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> Reported-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> kernel/trace/bpf_trace.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 95b6b3b16bac..2c064ba7b0bd 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2216,8 +2216,8 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
>
> old_array = bpf_event_rcu_dereference(event->tp_event->prog_array);
> ret = bpf_prog_array_copy(old_array, event->prog, NULL, 0, &new_array);
> - if (ret == -ENOENT)
> - goto unlock;
> + if (WARN_ON_ONCE(ret == -ENOENT))
> + goto put;
> if (ret < 0) {
> bpf_prog_array_delete_safe(old_array, event->prog);
seeing
if (ret < 0)
bpf_prog_array_delete_safe(old_array, event->prog);
I think neither ret == -ENOENT nor WARN_ON_ONCE is necessary, tbh. So
now I feel like just dropping WARN_ON_ONCE() is better.
> } else {
> @@ -2225,6 +2225,7 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
> bpf_prog_array_free_sleepable(old_array);
> }
>
> +put:
> bpf_prog_put(event->prog);
> event->prog = NULL;
>
> --
> 2.46.2
>
