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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 2576FC43464 for ; Sat, 19 Sep 2020 14:44:30 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 8E77B21741 for ; Sat, 19 Sep 2020 14:44:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="HvAmBzz4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E77B21741 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=linuxfoundation.org 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 silver.osuosl.org (Postfix) with ESMTP id 4702D20494; Sat, 19 Sep 2020 14:44:29 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id w8psiRnyJeGu; Sat, 19 Sep 2020 14:44:27 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 7805220464; Sat, 19 Sep 2020 14:44:26 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 5F766C088B; Sat, 19 Sep 2020 14:44:26 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 4A9A9C1AD5 for ; Sat, 19 Sep 2020 14:44:25 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 249DA8738F for ; Sat, 19 Sep 2020 14:44:25 +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 QotmGJSIE6BX for ; Sat, 19 Sep 2020 14:44:24 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by whitealder.osuosl.org (Postfix) with ESMTPS id 4EAD987378 for ; Sat, 19 Sep 2020 14:44:24 +0000 (UTC) Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5B8912098B; Sat, 19 Sep 2020 14:44:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600526663; bh=Bxl5ZkjXMp2TPSkn3hGdRJLWXUhCroTIN94qZJ785hM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HvAmBzz4j84+nW2I/6iTGG7u+tu/+fVFlTymgUy9x48ZHF94OcJYcK3VRxYLyYTyb gLdVK3Jz7CFYgGvvk2LFTH6hxIvgXGihiig+gwgxNnILZPGg1qc84/ZJiaXzrUMjzZ 9BfhiCQpyntL37/8AEdpoY9xJH4Lfe+mv81k+IoQ= Date: Sat, 19 Sep 2020 16:44:51 +0200 From: Greg KH To: Al Viro Message-ID: <20200919144451.GF2712238@kroah.com> References: <20200916052657.18683-1-anant.thazhemadam@gmail.com> <20200916054157.GC825@sol.localdomain> <20200917002238.GO3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200917002238.GO3421308@ZenIV.linux.org.uk> Cc: Anant Thazhemadam , syzbot+4191a44ad556eacc1a7a@syzkaller.appspotmail.com, linux-kernel@vger.kernel.org, Eric Biggers , linux-fsdevel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.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 Thu, Sep 17, 2020 at 01:22:38AM +0100, Al Viro wrote: > 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. Reproducer is pretty simple: https://syzkaller.appspot.com/text?tag=ReproC&x=13974b2f100000 Now if that is actually valid or not, I don't know... thanks, greg k-h _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees