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_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 D7B28C76188 for ; Wed, 17 Jul 2019 03:21:00 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 6A53E20818 for ; Wed, 17 Jul 2019 03:21:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A53E20818 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=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45pMwp1qSRzDqVr for ; Wed, 17 Jul 2019 13:20:58 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (mailfrom) smtp.mailfrom=ftp.linux.org.uk (client-ip=195.92.253.2; helo=zeniv.linux.org.uk; envelope-from=viro@ftp.linux.org.uk; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [195.92.253.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45pMY80P7zzDqBx for ; Wed, 17 Jul 2019 13:03:55 +1000 (AEST) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92 #3 (Red Hat Linux)) id 1hnaDa-0008R1-HC; Wed, 17 Jul 2019 03:02:58 +0000 Date: Wed, 17 Jul 2019 04:02:58 +0100 From: Al Viro To: Rich Felker Subject: Re: [PATCH v2 2/4] Add fchmodat4(), a new syscall Message-ID: <20190717030258.GT17978@ZenIV.linux.org.uk> References: <20190717012719.5524-1-palmer@sifive.com> <20190717012719.5524-3-palmer@sifive.com> <20190717024046.GI1506@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190717024046.GI1506@brightrain.aerifal.cx> User-Agent: Mutt/1.11.3 (2019-02-01) X-Mailman-Approved-At: Wed, 17 Jul 2019 13:17:29 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kim.phillips@arm.com, catalin.marinas@arm.com, linux-sh@vger.kernel.org, peterz@infradead.org, Palmer Dabbelt , heiko.carstens@de.ibm.com, stefan@agner.ch, linux-mips@vger.kernel.org, James.Bottomley@hansenpartnership.com, namhyung@kernel.org, paulus@samba.org, deepa.kernel@gmail.com, hpa@zytor.com, sparclinux@vger.kernel.org, linux-ia64@vger.kernel.org, will@kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, hare@suse.com, gor@linux.ibm.com, ysato@users.sourceforge.jp, deller@gmx.de, x86@kernel.org, linux@armlinux.org.uk, borntraeger@de.ibm.com, mingo@redhat.com, geert@linux-m68k.org, linux-arm-kernel@lists.infradead.org, jhogan@kernel.org, firoz.khan@linaro.org, mattst88@gmail.com, fenghua.yu@intel.com, Arnd Bergmann , jolsa@redhat.com, tycho@tycho.ws, acme@kernel.org, schwidefsky@de.ibm.com, linux-m68k@lists.linux-m68k.org, ink@jurassic.park.msu.ru, luto@kernel.org, alexander.shishkin@linux.intel.com, tglx@linutronix.de, christian@brauner.io, rth@twiddle.net, axboe@kernel.dk, dhowells@redhat.com, monstr@monstr.eu, tony.luck@intel.com, linux-parisc@vger.kernel.org, linux-api@vger.kernel.org, Linus Torvalds , linux-kernel@vger.kernel.org, ralf@linux-mips.org, paul.burton@mips.com, linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org, bp@alien8.de, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jul 16, 2019 at 10:40:46PM -0400, Rich Felker wrote: > On Tue, Jul 16, 2019 at 06:27:17PM -0700, Palmer Dabbelt wrote: > > man 3p says that fchmodat() takes a flags argument, but the Linux > > syscall does not. There doesn't appear to be a good userspace > > workaround for this issue but the implementation in the kernel is pretty > > straight-forward. The specific use case where the missing flags came up > > was WRT a fuse filesystem implemenation, but the functionality is pretty > > generic so I'm assuming there would be other use cases. > > Note that we do have a workaround in musl libc with O_PATH and > /proc/self/fd, but a syscall that allows a proper fix with the ugly > workaround only in the fallback path for old kernels will be much > appreciated! > > What about also doing a new SYS_faccessat4 with working AT_EACCESS > flag? The workaround we have to do for it is far worse. Umm... That's doable, but getting into the "don't switch creds unless needed" territory. I'll need to play with that a bit and see what gives a tolerable variant... What of this part wrt AT_EACCESS? if (!issecure(SECURE_NO_SETUID_FIXUP)) { /* Clear the capabilities if we switch to a non-root user */ kuid_t root_uid = make_kuid(override_cred->user_ns, 0); if (!uid_eq(override_cred->uid, root_uid)) cap_clear(override_cred->cap_effective); else override_cred->cap_effective = override_cred->cap_permitted; }