From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2574516EC0B for ; Fri, 21 Jun 2024 09:16:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718961377; cv=none; b=l8zUGe4tAm/GBKbHq/NTt4c17ggORfxpmEFDhtdnCrV6yoHcWgbm93fx8Szu1tqDKH1B18ZdmuQKjQDQGDEMfockOgJp4aMpyKeW/UiNi+FgL4E+wCme2sYmztvjYHG3f77EJ8BWk1XXm8ajaXWblZbdXI83rIrDnZd8s/OuP+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718961377; c=relaxed/simple; bh=5XJeijBFwMIAQTzHMcx3zvbS0cEEi69GXEIlzTUup14=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GaIOL7LCJCJmXnwMswtuiYyjmB1cSgBNqtQZB4AFtkJmpXxyx3a+uoqy+PhVLZXvNWBMccRCg858PYDDGj9G1yvCYuBoH1GAC2pG17b9JYD4QYhgkv0R++dUIoqzT3fudlPg3UWoR3KPe98zA6vhFeWq+CUairZfiun8ZHOt65I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RS5d0SOZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RS5d0SOZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 021D7C32781; Fri, 21 Jun 2024 09:16:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1718961376; bh=5XJeijBFwMIAQTzHMcx3zvbS0cEEi69GXEIlzTUup14=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RS5d0SOZKDThKmdrWuPx65fT4JYdZp3xrJk3KwhRXbvClNnTCj8H1NboF+wRr9waK KosG5uIJWaPc0q0/OwFWCKMortW5EY+nWOut7S3wMcth4HQnsVMBZiCag8/aYthXwM Pn9JNun3+8Z4nYVwmeBOoHJCiOJZYFB5in2mj3cR66+uwXyUI181BA/ZCWLQHI9rI7 21O34WCCRZSRwgQpmgIYJB4jLvmKbGUSG5tE4YPHLJx1qoY3nwlKYGRMSv2yPQ866B 469xO1YUEbqrWp7R2kySxRWrIkec/OLi2cmWVHL6+dJE8VrtOOUXoCz826ygLMpWFj X+wg0pVaZzzkQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Sebastian Andrzej Siewior Subject: [PATCH 3/4] perf: Fix event leak upon exit Date: Fri, 21 Jun 2024 11:16:00 +0200 Message-ID: <20240621091601.18227-4-frederic@kernel.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240621091601.18227-1-frederic@kernel.org> References: <20240621091601.18227-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When a task is scheduled out, pending sigtrap deliveries are deferred to the target task upon resume to userspace via task_work. However failures while adding an event's callback to the task_work engine are ignored. And since the last call for events exit happen after task work is eventually closed, there is a small window during which pending sigtrap can be queued though ignored, leaking the event refcount addition such as in the following scenario: TASK A ----- do_exit() exit_task_work(tsk); perf_event_overflow() event->pending_sigtrap = pending_id; irq_work_queue(&event->pending_irq); =========> PREEMPTION: TASK A -> TASK B event_sched_out() event->pending_sigtrap = 0; atomic_long_inc_not_zero(&event->refcount) // FAILS: task work has exited task_work_add(&event->pending_task) [...] perf_pending_irq() // early return: event->oncpu = -1 [...] =========> TASK B -> TASK A perf_event_exit_task(tsk) perf_event_exit_event() free_event() WARN(atomic_long_cmpxchg(&event->refcount, 1, 0) != 1) // leak event due to unexpected refcount == 2 As a result the event is never released while the task exits. Fix this with appropriate task_work_add()'s error handling. Fixes: 517e6a301f34 ("perf: Fix perf_pending_task() UaF") Signed-off-by: Frederic Weisbecker --- kernel/events/core.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 8f908f077935..7c3218d31d1d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2284,18 +2284,15 @@ event_sched_out(struct perf_event *event, struct perf_event_context *ctx) } if (event->pending_sigtrap) { - bool dec = true; - event->pending_sigtrap = 0; if (state != PERF_EVENT_STATE_OFF && - !event->pending_work) { - event->pending_work = 1; - dec = false; + !event->pending_work && + !task_work_add(current, &event->pending_task, TWA_RESUME)) { WARN_ON_ONCE(!atomic_long_inc_not_zero(&event->refcount)); - task_work_add(current, &event->pending_task, TWA_RESUME); - } - if (dec) + event->pending_work = 1; + } else { local_dec(&event->ctx->nr_pending); + } } perf_event_set_state(event, state); -- 2.45.2