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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 AF490C433DB for ; Fri, 15 Jan 2021 12:05:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 78EFB23128 for ; Fri, 15 Jan 2021 12:05:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728464AbhAOMFY (ORCPT ); Fri, 15 Jan 2021 07:05:24 -0500 Received: from mx2.suse.de ([195.135.220.15]:57274 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726182AbhAOMFX (ORCPT ); Fri, 15 Jan 2021 07:05:23 -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=1610712277; 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=4/61Uo+zlVSdS9m3wBubDsgiAraVweiD6lOY4/ZHTuQ=; b=VUXxejLJskK+1kr9KssNyMhEnJE/9aY5YoowNaVo6ieN3RYsotlT0vx/RJ6bgI4o7dXbSp BcP+6lku6BvhF8cZbS2dWznCfEi//oQcVmQWps5JTkCbCzKGnUnu8qefK9fNV8rNyBpTL3 M4606OOBLlGjgSYYYAgL4sG/D2CQst4= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8D18CAC63; Fri, 15 Jan 2021 12:04:37 +0000 (UTC) Date: Fri, 15 Jan 2021 13:04:36 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , 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: <20210114170412.4819-1-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Reviewed-by: Petr Mladek Best Regards, Petr