From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B43532EEE80 for ; Wed, 12 Aug 2026 15:50:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786549839; cv=none; b=sSj9zAksVfPQeit4Ude4mC+pgNqt86c88DwvCRaJPz2OychG/Wk9QjPseFm/AYk15WyPbIEBH3xKegzSeoXV3ssPH827VsNlEXjpL1pYYPqocC99Stkxui41mQgPDYh982Bkuz+2yEtlX/k23W2W2JXiyQt0DZo+UALhHQVocKQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786549839; c=relaxed/simple; bh=CH9RfYmrzTDweBmCvwGXyCZ1Mr/x6oXi19Mwt4aTmpE=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=qGEtVnjHcIelSGa4qzeez87aHhhjcfPNcCcjkIk/QOubeX1fE6qQw3GAeAclutExpMm1AGd4SlMY/uEMtxhvVrxvyBl+xLt24GZ34avSmuOPvU0zg8bbOgPohVD/xGcEX2d9FlC/R68WskqCxamjCv8pZENm5j/iuFENzzNryEU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JkwaHLlP; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JkwaHLlP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 516A31F000E9; Wed, 12 Aug 2026 15:50:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786549838; bh=7bLVmUiqleuI1Xhrohc7JlnyHfdl8p8kN+pQSc7XV/4=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=JkwaHLlP7B6wq6yb3RCzRNREHb5trqTkmeZCkSL1DT9T1uFvIaRl2TscULSxa8X01 PRKluo/rhqFK0484MMBrhdFuNde5hCRZVTRF+MIhBwXXgExjrEqBvvQRmbujzXoB5U m2WpoartCEN20Ottm+Ms35tfhtGdIooyEeYx6zOZHG3wc3RfOcvn2Qvczf8nunGJOG HgkHSdVgyZZj02zyMeovWlxrVfFl7pnXIAQO4/U/066YyIg2ew6VP949PpLMthO7xp tfJ59oJMapvAVU7ARwQFYvx1b50jccIcN0iAbBK6OHcSp6VXb4qD7I4+kgRbCIc/Bl WhRnz31weBY8g== From: sashiko-bot@kernel.org Subject: Re: [PATCH v4 1/9] ring-buffer: Free cpu_buffer->free_page with subbuf_order Reply-To: sashiko-reviews@lists.linux.dev To: "Vincent Donnefort" Cc: linux-trace-kernel@vger.kernel.org In-Reply-To: <20260812153311.2328812-2-vdonnefort@google.com> References: <20260812153311.2328812-1-vdonnefort@google.com> <20260812153311.2328812-2-vdonnefort@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Wed, 12 Aug 2026 15:50:37 +0000 Message-Id: <20260812155038.516A31F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: Pre-existing issues: - [Critical] Concurrent execution of sub-buffer order resizing (`ring_buffe= r_subbuf_order_set`) and read operations (`ring_buffer_alloc_read_page`, `r= ing_buffer_read_page`) can lead to out-of-bounds writes, use-after-free, an= d page allocator corruption due to mismatched synchronization. -- --- Patch [1]: [PATCH v4 1/9] ring-buffer: Free cpu_buffer->free_page with = subbuf_order --- commit 4100674474d6bd293fb872fecb17fc781ca58502 Author: Vincent Donnefort ring-buffer: Free cpu_buffer->free_page with subbuf_order =20 When sub-buffers use an order greater than 0, cpu_buffer->free_page is allocated with subbuf_order. Use the correct order for cpu_buffer->free_page. > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 2667992f0aa29..a3d28b2e2c94a 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -2631,7 +2631,7 @@ static void rb_free_cpu_buffer(struct ring_buffer_p= er_cpu *cpu_buffer) > free_buffer_page(bpage); > } > =20 > - free_page((unsigned long)cpu_buffer->free_page); > + free_pages((unsigned long)cpu_buffer->free_page, cpu_buffer->buffer->su= bbuf_order); [Severity: Critical] This isn't a bug introduced by this patch, but is it possible for a race condition between resizing and reading to lead to memory corruption? If thread A changes the sub-buffer size via /sys/kernel/tracing/buffer_subbuf_size_kb, ring_buffer_subbuf_order_set() updates buffer->subbuf_order locklessly globally before tearing down the CPU buffers and clearing their free_page. If thread B concurrently reads /sys/kernel/tracing/per_cpu/cpu0/trace_pipe_= raw via tracing_buffers_read(), it observes the new order and calls ring_buffer_alloc_read_page(). Because ring_buffer_subbuf_order_set() hasn't yet cleared cpu_buffer->free_page for this CPU (they use distinct locks), thread B pops the old page from free_page but tags it with the new order: kernel/trace/ring_buffer.c:ring_buffer_alloc_read_page() { ... bpage->order =3D buffer->subbuf_order; ... if (cpu_buffer->free_page) { bpage->data =3D cpu_buffer->free_page; cpu_buffer->free_page =3D NULL; } ... } Thread B then calls ring_buffer_read_page(). The lockless check passes because both match the new order: kernel/trace/ring_buffer.c:ring_buffer_read_page() { ... if (data_page->order !=3D buffer->subbuf_order) return -1; ... reader->page =3D data_page->data; } Could this allow the undersized old page to be swapped into the ring buffer as the reader_page, leading to an out-of-bounds write when a writer attempts to write large events?=20 It seems it could also cause page allocator corruption when a smaller page is later passed to free_pages() with a larger order. > kfree(cpu_buffer); > } --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260812153311.2328= 812-1-vdonnefort@google.com?part=3D1