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=-8.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8DEC0C282DD for ; Thu, 23 May 2019 10:25:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4B66321019 for ; Thu, 23 May 2019 10:25:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="uZJ1ml/S" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730575AbfEWKZV (ORCPT ); Thu, 23 May 2019 06:25:21 -0400 Received: from mail-yw1-f66.google.com ([209.85.161.66]:44829 "EHLO mail-yw1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727434AbfEWKZV (ORCPT ); Thu, 23 May 2019 06:25:21 -0400 Received: by mail-yw1-f66.google.com with SMTP id e74so2055017ywe.11; Thu, 23 May 2019 03:25:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=+NNHjqxy4cA1iR7igWdvYkQtAM2DdUoWQ0xcNKGlcUE=; b=uZJ1ml/SqGhO6uZamvp643xn91paeHnqdxomJBvL9LrsYcy8HSgeAjB/fF6RfDeAKw suZdXa7S2gd3yDtpE57xSS+ijPDHrJ5fiyz2PTg6IJI5MaViKze6osc2qKSDcTnFvFSJ 4/c62F8cPWHSY+JakXytNEFIvinZTDg75pTKNjZM+AMRdEPLl/03j44a1i8UV1CUU8xU 7nSEOqP3oWadaUwlRLXAjl2TTf1v6GaHm1KdFPEsRZ2Teo6f2Z2oV2uK1QM+TRgqTKO6 O1KkRhDgbnp1oQzd1h8J/L1F9bSk5O8iOo1b9AkYBGUexnd42PUu87SD8cGvbdeIs7qT I1+Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+NNHjqxy4cA1iR7igWdvYkQtAM2DdUoWQ0xcNKGlcUE=; b=AcGtL7x2ObQo3yF21KZ+clORQUY0BPExei6NvKBeFWUFexAzlDcLnmboKAzxSU4+GZ dI/wMjYkIS6rkVf5ZmnP92NQ6y0WZBF7WjrQUtFGxkag2SAm8dOq1CGa/s95J/sO7H6v 84vNIqpJdylOd/8byspGZHqsP0sTxPkiQBhmMgySZpJP4+nLYQs4kG9gUQQGIfPdW0cf YBgx28Sb5OXYNIeyAjiMaWggwhk2KA2yST9j8LX79LBvYkIRsmJa706MBgzN0UT6HS6A igy0uVgngJ1xBXB999FvEKFKSktU9ukjUejiffzTg88U4WXFCeNrDY2tpKEwEsXCKgOH A9sg== X-Gm-Message-State: APjAAAWirfEIa7n0nt2sfPST1e/CwKpsHX4RGNMGVaGMPMU0/79Hqe3m +dfEik3tsIUeSm9AIvHHvTmbZmlX1c563TAKd8U= X-Google-Smtp-Source: APXvYqw7w14u3jrVFRwPHVUPg848bC02eoNql2Zpmdzv1MBhrwImOVrrYWjfI+Bfq7H2/0t3f+tF/JPZHbDa8SJnPy8= X-Received: by 2002:a81:4f06:: with SMTP id d6mr30466460ywb.379.1558607120083; Thu, 23 May 2019 03:25:20 -0700 (PDT) MIME-Version: 1.0 References: <20190522163150.16849-1-christian@brauner.io> <20190523095506.nyei5nogvv63lm4a@brauner.io> In-Reply-To: <20190523095506.nyei5nogvv63lm4a@brauner.io> From: Amir Goldstein Date: Thu, 23 May 2019 13:25:08 +0300 Message-ID: Subject: Re: [PATCH] fanotify: remove redundant capable(CAP_SYS_ADMIN)s To: Christian Brauner Cc: Jan Kara , linux-fsdevel , linux-kernel , Matthew Bobrowski Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 23, 2019 at 12:55 PM Christian Brauner wrote: > > On Wed, May 22, 2019 at 11:00:22PM +0300, Amir Goldstein wrote: > > On Wed, May 22, 2019 at 9:57 PM Christian Brauner wrote: > > > > > > On May 22, 2019 8:29:37 PM GMT+02:00, Amir Goldstein wrote: > > > >On Wed, May 22, 2019 at 7:32 PM Christian Brauner > > > > wrote: > > > >> > > > >> This removes two redundant capable(CAP_SYS_ADMIN) checks from > > > >> fanotify_init(). > > > >> fanotify_init() guards the whole syscall with capable(CAP_SYS_ADMIN) > > > >at the > > > >> beginning. So the other two capable(CAP_SYS_ADMIN) checks are not > > > >needed. > > > > > > > >It's intentional: > > > > > > > >commit e7099d8a5a34d2876908a9fab4952dabdcfc5909 > > > >Author: Eric Paris > > > >Date: Thu Oct 28 17:21:57 2010 -0400 > > > > > > > > fanotify: limit the number of marks in a single fanotify group > > > > > > > >There is currently no limit on the number of marks a given fanotify > > > >group > > > >can have. Since fanotify is gated on CAP_SYS_ADMIN this was not seen > > > >as > > > >a serious DoS threat. This patch implements a default of 8192, the > > > >same as > > > >inotify to work towards removing the CAP_SYS_ADMIN gating and > > > >eliminating > > > > the default DoS'able status. > > > > > > > > Signed-off-by: Eric Paris > > > > > > > >There idea is to eventually remove the gated CAP_SYS_ADMIN. > > > >There is no reason that fanotify could not be used by unprivileged > > > >users > > > >to setup inotify style watch on an inode or directories children, see: > > > >https://patchwork.kernel.org/patch/10668299/ > > > > > > > >> > > > >> Fixes: 5dd03f55fd2 ("fanotify: allow userspace to override max queue > > > >depth") > > > >> Fixes: ac7e22dcfaf ("fanotify: allow userspace to override max > > > >marks") > > > > > > > >Fixes is used to tag bug fixes for stable. > > > >There is no bug. > > > > > > > >Thanks, > > > >Amir. > > > > > > Interesting. When do you think the gate can be removed? > > > > Nobody is working on this AFAIK. > > What I posted was a simple POC, but I have no use case for this. > > In the patchwork link above, Jan has listed the prerequisites for > > removing the gate. > > > > One of the prerequisites is FAN_REPORT_FID, which is now merged. > > When events gets reported with fid instead of fd, unprivileged user > > (hopefully) cannot use fid for privilege escalation. > > > > > I was looking into switching from inotify to fanotify but since it's not usable from > > > non-initial userns it's a no-no > > > since we support nested workloads. > > > > One of Jan's questions was what is the benefit of using inotify-compatible > > fanotify vs. using inotify. > > So what was the reason you were looking into switching from inotify to fanotify? > > Is it because of mount/filesystem watch? Because making those available for > > Yeah. Well, I would need to look but you could probably do it safely for > filesystems mountable in user namespaces (which are few). > Can you do a bind-mount and then place a watch on the bind-mount or is > this superblock based? > Either. FAN_MARK_MOUNT was there from day 1 of fanotify. FAN_MARK_FILESYSTEM was merged to Linux Linux 4.20. But directory modification events that are supported since v5.1 are not available with FAN_MARK_MOUNT, see: https://github.com/amir73il/man-pages/blob/fanotify_fid/man2/fanotify_init.2#L97 Matthew, Perhaps this fact is worth a mention in the linked entry for FAN_REPORT_FID in fanotify_init.2 in addition to the comment on the entry for FAN_MARK_MOUNT in fanotify_mark.2. Thanks, Amir.