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([2405:201:682f:383f:707f:3e47:3c20:b84e]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1416ad53874sm32078704c88.4.2026.08.20.18.42.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Aug 2026 18:42:27 -0700 (PDT) From: Deepanshu Kartikey To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, olsajiri@gmail.com, irogers@google.com, adrian.hunter@intel.com, james.clark@linaro.org, kpsingh@kernel.org, matt@bobrowski.net, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, emil@etsalapatis.com, ihor.solodrai@linux.dev, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Deepanshu Kartikey Subject: [PATCH] perf/bpf: Fix lockless access to parent_event->prog in perf_event_alloc() Date: Fri, 21 Aug 2026 07:12:10 +0530 Message-ID: <20260821014210.18681-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit During fork(), perf_event_alloc() reads parent_event->prog locklessly which can race with a concurrent bpf_perf_link_release() clearing and freeing the prog via perf_event_detach_bpf_prog(). This can result in a NULL pointer dereference or use-after-free in bpf_prog_inc(). Fix by holding bpf_event_mutex when inheriting the BPF program during fork(). Make bpf_event_mutex non-static and declare it extern in perf_event.h so it is accessible from kernel/events/core.c. Fixes: 85192dbf4de0 ("bpf: Convert bpf_prog refcnt to atomic64_t") Signed-off-by: Deepanshu Kartikey --- include/linux/perf_event.h | 2 ++ kernel/events/core.c | 8 +++++--- kernel/trace/bpf_trace.c | 2 +- 3 files changed, 8 insertions(+), 4 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 48d851fbd8ea..5c6dabb6dccb 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -2136,4 +2136,6 @@ static inline void perf_lopwr_cb(bool mode) } #endif +extern struct mutex bpf_event_mutex; + #endif /* _LINUX_PERF_EVENT_H */ diff --git a/kernel/events/core.c b/kernel/events/core.c index ba5bd6a78fe7..a89e33c47073 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -13433,12 +13433,15 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, overflow_handler = parent_event->overflow_handler; context = parent_event->overflow_handler_context; #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING) - if (parent_event->prog) { - struct bpf_prog *prog = parent_event->prog; - + struct bpf_prog *prog; + + mutex_lock(&bpf_event_mutex); + prog = parent_event->prog; + if (prog) { bpf_prog_inc(prog); event->prog = prog; } + mutex_unlock(&bpf_event_mutex); #endif } diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 75495a5c3507..730fc22a9daa 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1944,7 +1944,7 @@ const struct bpf_verifier_ops perf_event_verifier_ops = { const struct bpf_prog_ops perf_event_prog_ops = { }; -static DEFINE_MUTEX(bpf_event_mutex); +DEFINE_MUTEX(bpf_event_mutex); #define BPF_TRACE_MAX_PROGS 64 -- 2.43.0