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[2a00:1028:83a2:52b6:eb07:575d:6885:126a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3861ecf416fsm4952493f8f.16.2024.12.06.09.09.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Dec 2024 09:09:53 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Fri, 6 Dec 2024 18:09:51 +0100 To: Andrii Nakryiko Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Sean Young , Peter Zijlstra , bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo Subject: Re: [PATCH bpf] bpf,perf: Fix perf_event_detach_bpf_prog error handling Message-ID: References: <20241023100131.3400274-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Oct 23, 2024 at 09:01:02AM -0700, Andrii Nakryiko wrote: > On Wed, Oct 23, 2024 at 3:01 AM Jiri Olsa 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 > > Fixes: 170a7e3ea070 ("bpf: bpf_prog_array_copy() should return -ENOENT if exclude_prog not found") > > Closes: https://lore.kernel.org/lkml/20241022111638.GC16066@noisy.programming.kicks-ass.net/ > > Reported-by: Peter Zijlstra > > Signed-off-by: Jiri Olsa > > --- > > 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. hi, there's syzbot report [1] where we could end up with following - create perf event and set bpf program to it - clone process -> create inherited event - exit -> release both events - first perf_event_detach_bpf_prog call will release tp_event->prog_array and second perf_event_detach_bpf_prog will crash because tp_event->prog_array is NULL we can fix that quicly with change below, I guess we could add refcount to bpf_prog_array_item and allow one of the parent/inherited events to work while the other is gone.. but that might be too much, will check jirka [1] https://lore.kernel.org/bpf/Z1MR6dCIKajNS6nU@krava/T/#m91dbf0688221ec7a7fc95e896a7ef9ff93b0b8ad --- diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index fe57dfbf2a86..d4b45543ebc2 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2251,6 +2251,8 @@ void perf_event_detach_bpf_prog(struct perf_event *event) goto unlock; old_array = bpf_event_rcu_dereference(event->tp_event->prog_array); + if (!old_array) + goto put; ret = bpf_prog_array_copy(old_array, event->prog, NULL, 0, &new_array); if (ret < 0) { bpf_prog_array_delete_safe(old_array, event->prog); @@ -2259,6 +2261,7 @@ 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;