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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 820FBC433E2 for ; Thu, 17 Sep 2020 00:22:52 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C48FC20684 for ; Thu, 17 Sep 2020 00:22:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C48FC20684 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-kernel-mentees-bounces@lists.linuxfoundation.org Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 749D286F41; Thu, 17 Sep 2020 00:22:51 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id etRLc_dW_qgE; Thu, 17 Sep 2020 00:22:50 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by fraxinus.osuosl.org (Postfix) with ESMTP id 2674B86F3C; Thu, 17 Sep 2020 00:22:50 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 0A04DC0859; Thu, 17 Sep 2020 00:22:50 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 3A05CC0051 for ; Thu, 17 Sep 2020 00:22:48 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 1658087834 for ; Thu, 17 Sep 2020 00:22:48 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id YqQkat8CAklU for ; Thu, 17 Sep 2020 00:22:46 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [195.92.253.2]) by whitealder.osuosl.org (Postfix) with ESMTPS id 8424C87825 for ; Thu, 17 Sep 2020 00:22:46 +0000 (UTC) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIhh8-0004tj-2A; Thu, 17 Sep 2020 00:22:38 +0000 Date: Thu, 17 Sep 2020 01:22:38 +0100 From: Al Viro To: Eric Biggers Message-ID: <20200917002238.GO3421308@ZenIV.linux.org.uk> References: <20200916052657.18683-1-anant.thazhemadam@gmail.com> <20200916054157.GC825@sol.localdomain> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200916054157.GC825@sol.localdomain> Cc: linux-fsdevel@vger.kernel.org, Anant Thazhemadam , linux-kernel-mentees@lists.linuxfoundation.org, syzbot+4191a44ad556eacc1a7a@syzkaller.appspotmail.com, linux-kernel@vger.kernel.org Subject: Re: [Linux-kernel-mentees] [PATCH] fs: fix KMSAN uninit-value bug by initializing nd in do_file_open_root X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" On Tue, Sep 15, 2020 at 10:41:57PM -0700, Eric Biggers wrote: > Looking at the actual KMSAN report, it looks like it's nameidata::dir_mode or > nameidata::dir_uid that is uninitialized. You need to figure out the correct > solution, not just blindly initialize with zeroes -- that could hide a bug. > Is there a bug that is preventing these fields from being initialized to the > correct values, are these fields being used when they shouldn't be, etc... False positive, and this is the wrong place to shut it up. ->dir_uid and ->dir_mode are set when link_path_walk() resolves the pathname to directory + final component. They are used when deciding whether to reject a trailing symlink (on fs.protected_symlinks setups) and whether to allow creation in sticky directories (on fs.protected_regular and fs.protected_fifos setups). Both operations really need the results of successful link_path_walk(). I don't see how that could be not a false positive. If we hit the use in may_create_in_sticky(), we'd need the combination of * pathname that consists only of slashes (or it will be initialized) * LAST_NORM in nd->last_type, which is flat-out impossible, since we are left with LAST_ROOT for such pathnames. The same goes for may_follow_link() use - we need WALK_TRAILING in flags to hit it in the first place, which can come from two sources - return walk_component(nd, WALK_TRAILING); in lookup_last() (and walk_component() won't go anywhere near the call chain leading to may_follow_link() without LAST_NORM in nd->last_type) and res = step_into(nd, WALK_TRAILING, dentry, inode, seq); in open_last_lookups(), which also won't go anywhere near that line without LAST_NORM in the nd->last_type. IOW, unless we manage to call that without having called link_path_walk() at all or after link_path_walk() returning an error, we shouldn't hit that. And if we *do* go there without link_path_walk() or with an error from link_path_walk(), we have a much worse problem. I want to see the details of reproducer. If it's for real, we have a much more serious problem; if it's a false positive, the right place to deal with it would be elsewhere (perhaps on return from link_path_walk() with a slashes-only pathname), but in any case it should only be done after we manage to understand what's going on. _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees