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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 B9B88ECDE30 for ; Wed, 17 Oct 2018 12:10:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7333A2150F for ; Wed, 17 Oct 2018 12:10:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7333A2150F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727136AbeJQUFe (ORCPT ); Wed, 17 Oct 2018 16:05:34 -0400 Received: from ozlabs.org ([203.11.71.1]:51815 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726996AbeJQUFe (ORCPT ); Wed, 17 Oct 2018 16:05:34 -0400 Received: by ozlabs.org (Postfix, from userid 1034) id 42ZrbM2MTlz9sC2; Wed, 17 Oct 2018 23:10:07 +1100 (AEDT) From: Michael Ellerman To: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH] seq_buf: Make seq_buf_puts() NULL terminate the buffer Date: Wed, 17 Oct 2018 23:10:00 +1100 Message-Id: <20181017121000.30240-1-mpe@ellerman.id.au> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently seq_buf_puts() will happily create a non NULL terminated string for you in the buffer. This is particularly dangerous if the buffer is on the stack. For example: char buf[8]; char secret = "secret"; struct seq_buf s; seq_buf_init(&s, buf, sizeof(buf)); seq_buf_puts(&s, "foo"); printk("Message is %s\n", buf); Can result in: Message is fooªªªªªsecret We could require all users to memset() their buffer to NULL before use. But that seems likely to be forgotten and lead to bugs. Instead we can change seq_buf_puts() to always leave the buffer in a NULL terminated state. The only downside is that this makes the buffer 1 character smaller for seq_buf_puts(), but that seems like a good trade off. Signed-off-by: Michael Ellerman --- lib/seq_buf.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) I recently merged a patch which actually hit this behaviour. I worked around it by using seq_buf_printf(), but it would be good to fix the problem at the source. diff --git a/lib/seq_buf.c b/lib/seq_buf.c index 11f2ae0f9099..b1570204cde3 100644 --- a/lib/seq_buf.c +++ b/lib/seq_buf.c @@ -144,9 +144,13 @@ int seq_buf_puts(struct seq_buf *s, const char *str) WARN_ON(s->size == 0); + /* Add 1 to len for the trailing NULL which must be there */ + len += 1; + if (seq_buf_can_fit(s, len)) { memcpy(s->buffer + s->len, str, len); - s->len += len; + /* Don't count the trailing NULL against the capacity */ + s->len += len - 1; return 0; } seq_buf_set_overflow(s); -- 2.17.1