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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 E11EBC606B0 for ; Tue, 9 Jul 2019 10:12:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B84D0205F4 for ; Tue, 9 Jul 2019 10:12:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="dmj8AnZu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726309AbfGIKMg (ORCPT ); Tue, 9 Jul 2019 06:12:36 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:35734 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725989AbfGIKMf (ORCPT ); Tue, 9 Jul 2019 06:12:35 -0400 Received: by mail-pl1-f195.google.com with SMTP id w24so9837699plp.2 for ; Tue, 09 Jul 2019 03:12:35 -0700 (PDT) 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:user-agent; bh=RhoR5GKsIFoTSiglLtCPA0A3UUuVIpZh8wOmabYfUC8=; b=dmj8AnZuLaqSXh4uEkr1ENxbRurhbd7SgTiXb64qUqSn7UBNckooPSHNDizjJ54xma OJj/cKzNijTV2vlddX6zUQx1oNkKNvHF//HUww44WvA9nkkqxHg4eUr8QvJy/hOxagUu Xq6ZzJMn/GiN+X6TVEDHEDhDZNOcDlvFrYA/0iKtxk503kHJ96KyC5f/FHt0aEjCLFeZ +L1yOkxI7cS/nNa92OZu5SlhapqaoN8eEKWMXk9pBJBw3UE2JmkISmPgfCqh1mxXH/rT Kv7aQaqrqW6A96YYQdXRsaF5/S+7ECYessQ/8MRGcVrPPzeIDxLt8hBJdFovOV2J42ct HSCQ== 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:user-agent; bh=RhoR5GKsIFoTSiglLtCPA0A3UUuVIpZh8wOmabYfUC8=; b=DKqxcCVj2uI7kYb6EKt3rPsQXEJ7Xu+Xw6Q8+IYabsDAuPAzZKU3O23y1ufnMFuSxL wIjFWkQ3aAzcWVmh4vHZuEVuFS4OrExWHw2SFTofZEcuHRctBooHLLiH2qIQ2XjPDy9n zK0ExG1CFZYLF47bZ38QMJOQqtNBt66Aue+tOEuWzHHlXsn3hRNJ6TAjBJOwQR/EW5YJ JCSZMnYjEZQ7fc3OIZEqviE73zJHti1D449oZDbJFFWMvd+Jdpx8L71FsP0YYyRlAs6q EQ7w0/2e40qaRYxsHFmDtWkt/2lOie06OoMw94Dx3/eS1NxZpuOTMzjYaY/cS6T9UUzc g45Q== X-Gm-Message-State: APjAAAVbgI2g1N4fj+/b2MecYkBMs/uoRPR0SgCeGxhm+oOc+qu/dcNG B9gDHREczX7dEBOPniONlgJh/TSe X-Google-Smtp-Source: APXvYqxrlyide7O9/j67bE6YvuyRXra94KwadyVuZPptMBTR/P/TVevLXGFaTWQRfhzagFenfCErig== X-Received: by 2002:a17:902:20ec:: with SMTP id v41mr29202567plg.142.1562667155186; Tue, 09 Jul 2019 03:12:35 -0700 (PDT) Received: from localhost ([175.223.48.34]) by smtp.gmail.com with ESMTPSA id 33sm18563562pgy.22.2019.07.09.03.12.33 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 09 Jul 2019 03:12:34 -0700 (PDT) Date: Tue, 9 Jul 2019 19:12:30 +0900 From: Sergey Senozhatsky To: Vincent Whitchurch Cc: pmladek@suse.com, sergey.senozhatsky@gmail.com, rostedt@goodmis.org, linux-kernel@vger.kernel.org, Vincent Whitchurch Subject: Re: [PATCH] printk: Do not lose last line in kmsg dump Message-ID: <20190709101230.GA16909@jagdpanzerIV> References: <20190709081042.31551-1-vincent.whitchurch@axis.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190709081042.31551-1-vincent.whitchurch@axis.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (07/09/19 10:10), Vincent Whitchurch wrote: > A dump of a 64-byte buffer filled by kmsg_dump_get_buffer(), before this > patch: > > 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 35 32 32 31 39 37 <0>[ 6.522197 > 00000010: 5d 20 41 41 41 41 41 41 41 41 41 41 41 41 41 0a ] AAAAAAAAAAAAA. > 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > After this patch: > > 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 34 32 37 35 30 32 <0>[ 6.427502 > 00000010: 5d 20 41 41 41 41 41 41 41 41 41 41 41 41 41 0a ] AAAAAAAAAAAAA. > 00000020: 3c 30 3e 5b 20 20 20 20 36 2e 34 32 37 37 36 39 <0>[ 6.427769 > 00000030: 5d 20 42 42 42 42 42 42 42 42 31 32 33 34 35 0a ] BBBBBBBB12345. [..] > @@ -1318,7 +1318,7 @@ static size_t msg_print_text(const struct printk_log *msg, bool syslog, > } > > if (buf) { > - if (prefix_len + text_len + 1 >= size - len) > + if (prefix_len + text_len + 1 > size - len) > break; So with this patch the last byte of the buffer is 0xA. It's a bit uncomfortable that `len', which we return from msg_print_text(), now points one byte beyond the buffer: buf[len++] = '\n'; return len; This is not very common. Not sure what usually happens to kmsg_dump buffers, but anyone who'd do a rather innocent kmsg_dump(buf, &len); buf[len] = 0x00; will write to something which is not a kmsg buffer (in some cases). -ss