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Mon, 23 Nov 2020 11:24:39 -0500 (EST) Received: from mailfrontend1 ([10.202.2.162]) by compute6.internal (MEProxy); Mon, 23 Nov 2020 11:24:39 -0500 X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedujedrudegiedgledtucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepfffhvffukfhfgggtuggjsehttdertddttddvnecuhfhrohhmpefvhigthhho ucetnhguvghrshgvnhcuoehthigthhhosehthigthhhordhpihiiiigrqeenucggtffrrg htthgvrhhnpeegkeefjeegkedtjefgfeduleekueetjeeghffhuefgffefleehgeeifedv gfethfenucfkphepuddvkedruddtjedrvdeguddrudejgeenucevlhhushhtvghrufhiii gvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpehthigthhhosehthigthhhordhpihii iigr X-ME-Proxy: Received: from cisco (unknown [128.107.241.174]) by mail.messagingengine.com (Postfix) with ESMTPA id 652D83280060; Mon, 23 Nov 2020 11:24:30 -0500 (EST) Date: Mon, 23 Nov 2020 11:24:28 -0500 From: Tycho Andersen To: Christian Brauner Subject: Re: [PATCH v2 07/39] mount: attach mappings to mounts Message-ID: <20201123162428.GA24807@cisco> References: <20201115103718.298186-1-christian.brauner@ubuntu.com> <20201115103718.298186-8-christian.brauner@ubuntu.com> <20201123154719.GD4025434@cisco> MIME-Version: 1.0 In-Reply-To: <20201123154719.GD4025434@cisco> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-loop: linux-audit@redhat.com X-Mailman-Approved-At: Mon, 23 Nov 2020 11:30:29 -0500 Cc: Andy Lutomirski , Mimi Zohar , James Bottomley , Andreas Dilger , Christoph Hellwig , Jonathan Corbet , smbarber@chromium.org, Christoph Hellwig , Alban Crequy , linux-ext4@vger.kernel.org, Mrunal Patel , Arnd Bergmann , Jann Horn , selinux@vger.kernel.org, Josh Triplett , Seth Forshee , Aleksa Sarai , Alexander Viro , Lennart Poettering , OGAWA Hirofumi , Geoffrey Thomas , David Howells , John Johansen , Theodore Tso , Dmitry Kasatkin , containers@lists.linux-foundation.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, "Eric W. Biederman" , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, Todd Kjos X-BeenThere: linux-audit@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Linux Audit Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=linux-audit-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Mon, Nov 23, 2020 at 10:47:19AM -0500, Tycho Andersen wrote: > On Sun, Nov 15, 2020 at 11:36:46AM +0100, Christian Brauner wrote: > > +static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt) > > +{ > > + return mnt->mnt_user_ns; > > +} > > I think you might want a READ_ONCE() here. Right now it seems ok, since the > mnt_user_ns can't change, but if we ever allow it to change (and I see you have > a idmapped_mounts_wip_v2_allow_to_change_idmapping branch on your public tree > :D), the pattern of, > > user_ns = mnt_user_ns(path->mnt); > if (mnt_idmapped(path->mnt)) { > uid = kuid_from_mnt(user_ns, uid); > gid = kgid_from_mnt(user_ns, gid); > } > > could race. Actually, isn't a race possible now? kuid_from_mnt(mnt_user_ns(path->mnt) /* &init_user_ns */); WRITE_ONCE(mnt->mnt.mnt_user_ns, user_ns); WRITE_ONCE(m->mnt.mnt_flags, flags); kgid_from_mnt(mnt_user_ns(path->mnt) /* the right user ns */); So maybe it should be: if (mnt_idmapped(path->mnt)) { barrier(); user_ns = mnt_user_ns(path->mnt); uid = kuid_from_mnt(user_ns, uid); gid = kgid_from_mnt(user_ns, gid); } since there's no data dependency between mnt_idmapped() and mnt_user_ns()? Tycho -- Linux-audit mailing list Linux-audit@redhat.com https://www.redhat.com/mailman/listinfo/linux-audit