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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 8A7C3C6778A for ; Sat, 7 Jul 2018 14:01:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F082208D9 for ; Sat, 7 Jul 2018 14:01:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F082208D9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org 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 S1753864AbeGGOBq (ORCPT ); Sat, 7 Jul 2018 10:01:46 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:52174 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753173AbeGGOBp (ORCPT ); Sat, 7 Jul 2018 10:01:45 -0400 Received: from localhost (unknown [37.168.185.56]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 50378D8E; Sat, 7 Jul 2018 14:01:44 +0000 (UTC) Date: Sat, 7 Jul 2018 16:01:40 +0200 From: Greg Kroah-Hartman To: Bernd Edlinger Cc: Tejun Heo , "linux-kernel@vger.kernel.org" Subject: Re: [PATCHv2] Fix range checks in kernfs_get_target_path Message-ID: <20180707140140.GA4941@kroah.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jul 07, 2018 at 09:41:03AM +0000, Bernd Edlinger wrote: > The strncpy causes a warning [-Wstringop-truncation] here, > which indicates that it never appends a NUL byte to the path. > The NUL byte is only there because the buffer is allocated > with kzalloc(PAGE_SIZE, GFP_KERNEL), but since the range-check > is also off-by-one, and PAGE_SIZE==PATH_MAX the returned string > will not be zero-terminated if it is exactly PATH_MAX characters. > Furthermore also the initial loop may theoretically exceed PATH_MAX > and cause a fault. > > Signed-off-by: Bernd Edlinger > --- > fs/kernfs/symlink.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c > index 08ccabd..c8b7d44a 100644 > --- a/fs/kernfs/symlink.c > +++ b/fs/kernfs/symlink.c > @@ -63,7 +63,10 @@ static int kernfs_get_target_path(struct kernfs_node > if (base == kn) > break; > > - strcpy(s, "../"); > + if ((s - path) + 3 >= PATH_MAX) > + return -ENAMETOOLONG; > + > + memcpy(s, "../", 3); > s += 3; > base = base->parent; > } > @@ -79,16 +82,17 @@ static int kernfs_get_target_path(struct kernfs_node > if (len < 2) > return -EINVAL; > len--; > - if ((s - path) + len > PATH_MAX) > + if ((s - path) + len >= PATH_MAX) > return -ENAMETOOLONG; > > /* reverse fillup of target string from target to base */ > kn = target; > + s[len] = '\0'; > while (kn->parent && kn != base) { > int slen = strlen(kn->name); > > len -= slen; > - strncpy(s + len, kn->name, slen); > + memcpy(s + len, kn->name, slen); > if (len) > s[--len] = '/'; > This last memcpy replacement has already been applied to my tree, from a patch from soeone else, so are you sure all of the other changes are also really needed? Why the extra \0 termination of a string that is already terminated? And why is the first memcpy replacement needed? gcc doesn't say anything about that, does it? thanks, greg k-h