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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD804C10F0D for ; Tue, 19 Jan 2021 11:39:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F13C22DD3 for ; Tue, 19 Jan 2021 11:39:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390428AbhASLcw (ORCPT ); Tue, 19 Jan 2021 06:32:52 -0500 Received: from mx2.suse.de ([195.135.220.15]:42146 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388820AbhASLUv (ORCPT ); Tue, 19 Jan 2021 06:20:51 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611055205; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hWu+DiewVvlL1LmVaj1P5EWMhhS1qD2S88iFimQfQiA=; b=u+9iQaqACTIILNUbsmGHGAbTTV7d8oElPwb1A8brtM67ZWjRmamG/cIfHT9MaljRbrWThU iNB2/TB6PE8l/K1fWGuMsJf5yOCsFk7lB4TQBTw5cFeNXhTT7vPpprKDn105hVdosXdNrA TpVj71TnbBKioWefssKs+RR6CQmqPRo= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D501DADE3; Tue, 19 Jan 2021 11:20:04 +0000 (UTC) Date: Tue, 19 Jan 2021 12:20:04 +0100 From: Petr Mladek To: Sergey Senozhatsky Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , linux-kernel@vger.kernel.org Subject: Re: [PATCH] printk: fix buffer overflow potential for print_text() Message-ID: References: <20210114170412.4819-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 2021-01-19 09:44:56, Sergey Senozhatsky wrote: > On (21/01/15 13:07), Petr Mladek wrote: > > On Fri 2021-01-15 13:04:37, Petr Mladek wrote: > > > On Thu 2021-01-14 18:10:12, John Ogness wrote: > > > > Before commit b6cf8b3f3312 ("printk: add lockless ringbuffer"), > > > > msg_print_text() would only write up to size-1 bytes into the > > > > provided buffer. Some callers expect this behavior and append > > > > a terminator to returned string. In particular: > > > > > > > > arch/powerpc/xmon/xmon.c:dump_log_buf() > > > > arch/um/kernel/kmsg_dump.c:kmsg_dumper_stdout() > > > > > > > > msg_print_text() has been replaced by record_print_text(), which > > > > currently fills the full size of the buffer. This causes a > > > > buffer overflow for the above callers. > > > > > > > > Change record_print_text() so that it will only use size-1 bytes > > > > for text data. Also, for paranoia sakes, add a terminator after > > > > the text data. > > > > > > > > And finally, document this behavior so that it is clear that only > > > > size-1 bytes are used and a terminator is added. > > > > > > > > Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer") > > > > Signed-off-by: John Ogness > > John, how did you spot these problems? > > FWIW, Acked-by: Sergey Senozhatsky The patch has been committed into printk/linux.git, branch printk-rework. Best Regards, Petr