From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2265823C4FF; Wed, 24 Jun 2026 23:12:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782342747; cv=none; b=U5aiJyks/qLI9fnoZe6d32LnMvAfW4bG1u7qivkOrF19twOklj1h8YVi0u7z8eSddZ6BgQU1vFE3+mOakhKI+jysT1N3/QYG+tvdz7cy8TW1M7Ij86XWgA4em5oSspidybSM3lInXtZohkGNmlH4vgnlJd8Tl4y4w7hLJiS2t5M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782342747; c=relaxed/simple; bh=jxafdzeDQQj+b3Z/xYBssuCs0wa6+9Wk8H/YWO9YvgQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hvqRnHQX7hI1/9pAEU/dKHmiOtgpas2GYHE7GWaPNGa0vDBqxdtvsWQRi9KiacZCcetTwk6P2cYxTJH2ZNN0NEYYXfIss/zUxvYWubMT+DmDcELtfciksoFwrufBhN9aiDsFqpY2PAxN9r09jAacRw4dLZCiqYsrVIoS7JgEtsQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=M92HitiV; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="M92HitiV" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=beOvvVn0+AejXo29fd8CNsSGWNMgqTX5RDnFJbYLSpQ=; b=M92HitiVOHC2b3xmlqSSUz7btr +5wkyjQtPor8VgLu7kfScVvaoXEml8uIMhgdn86RYe/rCJmavsPIYE37/cP9PZE6c6YydZAqnxjyq pUDn9ahlFr1ZldblX5YAvqzRVyIFQUTDJGzofpLSSQi3UC+PSQBbOl3Sna6ippTzQ2rGIMcbjOVrc wJdXpQatdEAPX4T8ed+5UcT7ROQVDPzNEUnNUQNps3cxJhNa7BcUelLhf6X64PiNFs4Sag1hcknA1 PSqyDQBtVop1QcCBulxcSY6Tb/frG2eFzu5WbI6iU0awQsd2rxf6EI4caJ20JJGSpFXJYY0k3vhul kupeaGVQ==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.99.4 #2 (Red Hat Linux)) id 1wcWlX-0000000C2pX-0Rxc; Wed, 24 Jun 2026 23:12:19 +0000 Date: Thu, 25 Jun 2026 00:12:19 +0100 From: Al Viro To: John Ericson Cc: Li Chen , Cong Wang , Christian Brauner , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Jan Kara , Jonathan Corbet , Shuah Khan , Kees Cook , Sergei Zimmerman , Farid Zakaria Subject: Re: [RFC] Null Namespaces Message-ID: <20260624231219.GL2636677@ZenIV> References: Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro On Wed, Jun 24, 2026 at 06:51:47PM -0400, John Ericson wrote: > #### Null mount namespace > > - requires: > > - null root file system: absolute paths don't work. > > - null current working directory: relative paths with traditional, > non-`*at` system calls (and `*at` ones using `AT_FDCWD`) don't work. > > - All operations relating to the "ambient" mount tree don't work. > > - `*at` operations with a file descriptor do work. Huh? The last bit looks contradicts the previous one - if you have an opened directory in a mount from some namespace, those `*at` operations with that descriptor *will* be seeing the mount tree of that namespace, whatever the hell is "ambient" supposed to mean. Either that, or you will be exposing whatever's overmounted in that mount, which is a huge can of worms.