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=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 CAE98C433E0 for ; Tue, 19 Jan 2021 00:45:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83513230FE for ; Tue, 19 Jan 2021 00:45:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732593AbhASAp4 (ORCPT ); Mon, 18 Jan 2021 19:45:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45354 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731683AbhASApk (ORCPT ); Mon, 18 Jan 2021 19:45:40 -0500 Received: from mail-pl1-x62f.google.com (mail-pl1-x62f.google.com [IPv6:2607:f8b0:4864:20::62f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 647C2C061573 for ; Mon, 18 Jan 2021 16:45:00 -0800 (PST) Received: by mail-pl1-x62f.google.com with SMTP id t6so9550367plq.1 for ; Mon, 18 Jan 2021 16:45:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=JAP6YVCRqPrNfCjZamoYP6iHXVfN5atOSvue0hsNHKQ=; b=HZFe9W/moOmSXp0oFiCPqW2Gyw43X9nEwXi56DYeAWYPeyoOsf6NZFx5ip9Tsfza7T /hCYBkuFPNGaGGwuGPJlrBSVN0qs65BZKzzvadCxW3pZAv80WNWyoyaj7Wmq8/M5498l Xt+RIMmuCiLlPUjGXopdFPme5419aMW+m442Are0PfOFryLBdh6t5WTnybOHhBbFRtqQ mMK8K4KTWc65qtS/km6cJBGj3ZFgvqxJpretfofLJT23DganvPIO3E2U/WLcxjWJNMDY TqhvJKU5T+ZAL0o1gcXcdaKF0VsPhrueqJ/rcA+hul2WDoIMQAPCXYiEiqGaqgnfBO2j P8cA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=JAP6YVCRqPrNfCjZamoYP6iHXVfN5atOSvue0hsNHKQ=; b=qg2Pj4aSOE3TwPZjL82B6b5lTASfGXbRqbVaXx/Q29AVHnV1BYF2IsYKX/eSSn2q9C Qealtbub9sllTksOBIp/P5U9wiaWr20f28QKslTlSdZZ+1XHYSEQpKUBvgP6m+/fKYLQ qP+uhp+N8aydc6FnfRZawphL2c6KurowWbAsnTa+CxY7Gbmz0KKFbIWQzjLO9nTIlJ+M rQZTYu5unr32dDfawHTXPYMUKaUXbl2SnfoDoLSGTsMjTb0c2H2YYaKPKfEXgELFFRmi rgZmQPIrxP2KUlWzuYN5cXrwzSlXowkP9jcHqFgPNmcWyRtPuCG6Rw3ChRvU1UOrJiN8 F8xA== X-Gm-Message-State: AOAM533mGrEEF0CIlptcPrwhESeMR4CZ1qEsfTB2KdwryuXYMrfvT1rp FE+amun4TgciywNyWaFggX5YGzva06EGgQ== X-Google-Smtp-Source: ABdhPJzHxn8Ko5Spo7auOLhGY6qGBbyx0cRAYzILCXCwrZiBGP8zTOxCizBGNqIXrrIbwARnT7NjyA== X-Received: by 2002:a17:90a:e006:: with SMTP id u6mr2024759pjy.201.1611017099801; Mon, 18 Jan 2021 16:44:59 -0800 (PST) Received: from localhost ([2409:10:2e40:5100:6e29:95ff:fe2d:8f34]) by smtp.gmail.com with ESMTPSA id m27sm269712pgn.62.2021.01.18.16.44.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Jan 2021 16:44:58 -0800 (PST) Date: Tue, 19 Jan 2021 09:44:56 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: John Ogness , 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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > I forgot one thing. We should add stable here: > > Cc: stable@vger.kernel.org # 5.10+ Good point. -ss