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bh=lJVPvZPFKUR6Xs1v0CURfJymdYmFOv0QSO2UfXLpSFM=; b=AaBnXVwWfiYLm2bQwykmRUl0ZvsQY765yR5+GqfnrsYR8x9U+bAZllVB3c/EXd5zuPxcix f4LT0fHpqjHojTvKS7iUkqzw9Yqjcul5a90H9JHmuFqVVa+1p5e3FFsbg0Aif3Rd+mkBqT XahQMqJrUMQa6ks5WlNWGpxnHc2sqWM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-81-xYHIBfUHO0emFnvZ2Y7mhQ-1; Wed, 03 Feb 2021 13:05:37 -0500 X-MC-Unique: xYHIBfUHO0emFnvZ2Y7mhQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0ABC8100F340; Wed, 3 Feb 2021 18:05:36 +0000 (UTC) Received: from work-vm (ovpn-115-70.ams2.redhat.com [10.36.115.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BC28060BFA; Wed, 3 Feb 2021 18:05:23 +0000 (UTC) Date: Wed, 3 Feb 2021 18:05:20 +0000 From: "Dr. David Alan Gilbert" To: Stefan Hajnoczi Subject: Re: [PATCH v4 3/3] virtiofsd: prevent opening of special files (CVE-2020-35517) Message-ID: <20210203180520.GO2950@work-vm> References: <20210203113719.83633-1-stefanha@redhat.com> <20210203113719.83633-4-stefanha@redhat.com> <20210203152850.GA3307@redhat.com> <20210203170237.0c98f95f@bahia.lan> <20210203160858.GC3307@redhat.com> <20210203170514.GL74271@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20210203170514.GL74271@stefanha-x1.localdomain> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.539, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mszeredi@redhat.com, Daniel Berrange , slp@redhat.com, Greg Kurz , qemu-devel@nongnu.org, virtio-fs@redhat.com, Alex Xu , P J P , Laszlo Ersek , Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Stefan Hajnoczi (stefanha@redhat.com) wrote: > On Wed, Feb 03, 2021 at 11:08:58AM -0500, Vivek Goyal wrote: > > On Wed, Feb 03, 2021 at 05:02:37PM +0100, Greg Kurz wrote: > > > On Wed, 3 Feb 2021 10:28:50 -0500 > > > Vivek Goyal wrote: > > > > > > > On Wed, Feb 03, 2021 at 11:37:19AM +0000, Stefan Hajnoczi wrote: > > > > > > > > [..] > > > > > @@ -1727,36 +1764,38 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, > > > > > > > > > > update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > > > > > > > > > - fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW, > > > > > - mode); > > > > > + /* Try to create a new file but don't open existing files */ > > > > > + fd = openat(parent_inode->fd, name, fi->flags | O_CREAT | O_EXCL, mode); > > > > > err = fd == -1 ? errno : 0; > > > > > + > > > > > lo_restore_cred(&old); > > > > > > > > > > - if (!err) { > > > > > - ssize_t fh; > > > > > - > > > > > - pthread_mutex_lock(&lo->mutex); > > > > > - fh = lo_add_fd_mapping(lo, fd); > > > > > - pthread_mutex_unlock(&lo->mutex); > > > > > - if (fh == -1) { > > > > > - close(fd); > > > > > - err = ENOMEM; > > > > > - goto out; > > > > > - } > > > > > + /* Ignore the error if file exists and O_EXCL was not given */ > > > > > + if (err && !(err == EEXIST && !(fi->flags & O_EXCL))) { > > > > > > > > Can this check be simplified to. > > > > if (err && (err == EEXIST && (fi->flags & O_EXCL)) { > > > > > > I guess you meant : > > > > > > if (err && (err != EEXIST || fi->flags & O_EXCL) { > > > > This sounds correct. I forgot to take into account that if error is > > not -EEXIST, we still want to bail out irrespective of O_EXCL. > > I thought about De Morgan's law too but found the OR expression is not > easier to read than the AND expression :(. If you prefer it written this > way I can change it though. I think the version that you put, matches your comment well; although it's a bit of a weird case where nesting a pair of ! makes sense. Dave > Stefan -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK