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Wed, 3 Feb 2021 16:14:41 -0500 (EST) Date: Wed, 3 Feb 2021 16:14:41 -0500 From: Vivek Goyal To: Stefan Hajnoczi Subject: Re: [PATCH v4 3/3] virtiofsd: prevent opening of special files (CVE-2020-35517) Message-ID: <20210203211441.GH3307@redhat.com> 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> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@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=vgoyal@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, qemu-devel@nongnu.org, Greg Kurz , "Dr. David Alan Gilbert" , virtio-fs@redhat.com, Alex Xu , P J P , Laszlo Ersek Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Feb 03, 2021 at 05:05:14PM +0000, Stefan Hajnoczi 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 personally find this one to read. And not because of AND but because of double logical negation (!x) in previous expression. But I am not particular about it. If you don't find it easier to read, I can live with previous one. Vivek