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 693642472B6 for ; Thu, 13 Aug 2026 13:54:40 +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=1786629281; cv=none; b=cNbr/qbfjbWnd/0p5T3CzwYuzKWTj0weu9il5Scsyf2sgYXCwxqDm/+HpGhmNgLZws8fUrk6TAAIcIYqWtov599z1U6QpWHEzaZqzF3B8abclYto8SBh760BlK8wpVEANkWnLnAOSFlR96fy769jxkWutGMLR/BEW9c4/lfuPn8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786629281; c=relaxed/simple; bh=oYYh+xtw+Ni/0G6WphOQdA01oQWf85+mQbiqn17MyMc=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=LIx6WMEr6AeQou/YKtVTWyMS6L7+3Wl1pXnxyfMDi+DC3fo4vOOl+KbrkVd5xSmy7z7A3EQBdNlxyQuVlVT09MQ48cdLqNdetTvLgVMVOovOvYNe+PvdmaA2SUgJlszUFlu8bRj3utKLuzKGKYmvcsYWF6E8oNw1GT1WMQFAdJo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ohgukKlD; 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="ohgukKlD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E42E01F000E9; Thu, 13 Aug 2026 13:54:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786629280; bh=i10DBpY8TblJA+ajP/lsy2Y/qXgecUeKczQjnCejPWM=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=ohgukKlDOaV0Wo5Ym/1Kk75robnBpViNmgT8b9F2ms0W85U1hWOdN60kdL57kJRGJ TRghYktt34CslGLQUuDll7+JGMIaBMYbSkaPeoLZ/9X0eQrUVEE3Vj0KYtSXkvGAnz jERBCOsMlHrJrRprpl7xWU7Wb+aJfI7+HIFXzqs+M7ZWYMPwfpOQLoe33uM4saMP+Q DfKofeMIMFto8W1HcosncWZKiLecirwXWqmlxQMpGgNi9V4FW6iY/IMpHCJG8PuUXL qeFrWjz0mJ5hOYxVET8EajnBo6jlRuoLHaHY6B+ZcKrxhUoP7soJycLjlMHufWTeCd USEZjhCRulYLQ== From: sashiko-bot@kernel.org Subject: Re: [PATCH v5 01/10] 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: <20260813131152.3589632-2-vdonnefort@google.com> References: <20260813131152.3589632-1-vdonnefort@google.com> <20260813131152.3589632-2-vdonnefort@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 13 Aug 2026 13:54:39 +0000 Message-Id: <20260813135439.E42E01F000E9@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] A data race and locking mismatch between `ring_buffer_subbuf_o= rder_set()`, `ring_buffer_alloc_read_page()`, and `ring_buffer_free_read_pa= ge()` allows `cpu_buffer->free_page` to cache a page of an old order while = `buffer->subbuf_order` reflects a new larger order. This leads to heap buff= er overflow and buddy allocator corruption. -- --- Patch [1]: [PATCH v5 01/10] ring-buffer: Free cpu_buffer::free_page wit= h subbuf_order --- commit f550c0bfeadcc22eca47316e1820b4d91f6ef261 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 is a pre-existing issue, but does this change expose a buddy allocator corruption if cpu_buffer->free_page contains a page of a smaller order than buffer->subbuf_order? A race condition between ring_buffer_subbuf_order_set() and=20 ring_buffer_free_read_page() can cause a smaller order page to be stashed in cpu_buffer->free_page while buffer->subbuf_order reflects a new larger order. If a trace reader calls ring_buffer_free_read_page(), it performs a lockless check of buffer->subbuf_order: kernel/trace/ring_buffer.c:ring_buffer_free_read_page() { ... if (page_ref_count(page) > 1 || data_page->order !=3D buffer->subbuf_order) goto out; ... } If a concurrent write to buffer_subbuf_size_kb calls ring_buffer_subbuf_order_set(), it updates buffer->subbuf_order without holding cpu_buffer->lock, and clears cpu_buffer->free_page under reader_lock. The trace reader then acquires cpu_buffer->lock and stashes the old smaller page into cpu_buffer->free_page, missing the clearance because of the lock mismatch (reader_lock vs cpu_buffer->lock): kernel/trace/ring_buffer.c:ring_buffer_free_read_page() { ... raw_spin_lock_irqsave(&cpu_buffer->lock, flags); if (!cpu_buffer->free_page) { cpu_buffer->free_page =3D dpage; ... } During teardown, free_pages() here would free the undersized page using the new larger order, causing buddy allocator corruption. Additionally, if a re= ader allocates this stashed page via ring_buffer_read_page(), it is swapped into the active ring buffer where writers will overflow its bounds. Can the locking be synchronized to prevent caching an old-order page? > =20 > kfree(cpu_buffer); > } --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260813131152.3589= 632-1-vdonnefort@google.com?part=3D1