From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F5BDE7C4E7 for ; Wed, 4 Oct 2023 18:08:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243850AbjJDSI3 (ORCPT ); Wed, 4 Oct 2023 14:08:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243818AbjJDSI2 (ORCPT ); Wed, 4 Oct 2023 14:08:28 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A3E8A6 for ; Wed, 4 Oct 2023 11:08:25 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E4AE4C433C8; Wed, 4 Oct 2023 18:08:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1696442905; bh=M/V2Tt9af+8Utlv68tTUR3iwA/FIi0LpvX54zB80O30=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HVC+gUkoU4ZsDlNxbiokwGFAVfZQF8eozkTieyPQSkbedjCLQSPodBQWxB356dQS7 mb2KJIRNedZEeQAVkSczHJk4fKHBSYUWYE/KZbLF9cAtuzOy9DN8btsrcC3GW/dDSL 6gremTlyjRjeRXn54/ZP0IhVA3Gpsfl9BJbbg4MU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Masami Hiramatsu , Mark Rutland , Tze-nan Wu , "Steven Rostedt (Google)" , Sasha Levin Subject: [PATCH 5.15 123/183] ring-buffer: Do not attempt to read past "commit" Date: Wed, 4 Oct 2023 19:55:54 +0200 Message-ID: <20231004175209.107104053@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231004175203.943277832@linuxfoundation.org> References: <20231004175203.943277832@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt (Google) [ Upstream commit 95a404bd60af6c4d9d8db01ad14fe8957ece31ca ] When iterating over the ring buffer while the ring buffer is active, the writer can corrupt the reader. There's barriers to help detect this and handle it, but that code missed the case where the last event was at the very end of the page and has only 4 bytes left. The checks to detect the corruption by the writer to reads needs to see the length of the event. If the length in the first 4 bytes is zero then the length is stored in the second 4 bytes. But if the writer is in the process of updating that code, there's a small window where the length in the first 4 bytes could be zero even though the length is only 4 bytes. That will cause rb_event_length() to read the next 4 bytes which could happen to be off the allocated page. To protect against this, fail immediately if the next event pointer is less than 8 bytes from the end of the commit (last byte of data), as all events must be a minimum of 8 bytes anyway. Link: https://lore.kernel.org/all/20230905141245.26470-1-Tze-nan.Wu@mediatek.com/ Link: https://lore.kernel.org/linux-trace-kernel/20230907122820.0899019c@gandalf.local.home Cc: Masami Hiramatsu Cc: Mark Rutland Reported-by: Tze-nan Wu Signed-off-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin --- kernel/trace/ring_buffer.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index b15d72284c7f7..69db849ae7dad 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2352,6 +2352,11 @@ rb_iter_head_event(struct ring_buffer_iter *iter) */ commit = rb_page_commit(iter_head_page); smp_rmb(); + + /* An event needs to be at least 8 bytes in size */ + if (iter->head > commit - 8) + goto reset; + event = __rb_page_index(iter_head_page, iter->head); length = rb_event_length(event); -- 2.40.1